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PerspectiveApril 14, 2016

Surface- and Tip-Enhanced Raman Spectroscopy in Catalysis
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Cite this: J. Phys. Chem. Lett. 2016, 7, 8, 1570–1584

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https://doi.org/10.1021/acs.jpclett.6b00147

Published April 14, 2016

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Abstract

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Surface- and tip-enhanced Raman spectroscopy (SERS and TERS) techniques exhibit highly localized chemical sensitivity, making them ideal for studying chemical reactions, including processes at catalytic surfaces. Catalyst structures, adsorbates, and reaction intermediates can be observed in low quantities at hot spots where electromagnetic fields are the strongest, providing ample opportunities to elucidate reaction mechanisms. Moreover, under ideal measurement conditions, it can even be used to trigger chemical reactions. However, factors such as substrate instability and insufficient signal enhancement still limit the applicability of SERS and TERS in the field of catalysis. By the use of sophisticated colloidal synthesis methods and advanced techniques, such as shell-isolated nanoparticle-enhanced Raman spectroscopy, these challenges could be overcome.

Subjects

Catalysis is essential in the field of sustainable chemistry because it allows reactions to take place more quickly, efficiently, and safely. (1-3) To improve chemical processes it is crucial to know how catalysts operate and how, why, and when they cease to work. Understanding the mechanism of all involved surface reactions in the case of heterogeneous catalysts is the key to designing the best possible catalytic materials. For this purpose, researchers use a wide variety of techniques. They originally used methods to study catalysts before and after reaction, such as spectroscopy, (electron) microscopy, and many more. Although these methods have greatly enhanced the understanding of catalysts, knowledge of actual operating catalysts remains incomplete. Understanding working catalysts requires the use of techniques that are able to identify when and where reactions take place, ultimately linking this information to the catalytic performance of these materials.

Valuable techniques for elucidating molecular structures are vibrational spectroscopy methods, including various forms of infrared (IR) (4-6) and Raman spectroscopy. (7-10) Raman spectroscopy enables the measurement of vibrational energy levels, which provide information about the molecular composition and structure within a sample. Operative under several different conditions, this spectroscopic technique has greatly improved the knowledge of both the syntheses (7, 8) and operation (9, 10) of catalytic solids. However, Raman spectroscopy lacks sensitivity due to the small Raman scattering cross section of analyte molecules. (11) The sensitivity of Raman spectroscopy can be enhanced using specialized techniques, of which resonance Raman, (11-14) coherent anti-Stokes Raman spectroscopy (CARS), (15) and surface-enhanced Raman spectroscopy (SERS) are the three most popular choices. (16) All of these techniques have their own strengths and weaknesses, but compared to the others, SERS exhibits a strong feature for catalysis: highly localized sensitivity. This local sensitivity can be exploited to sense surface species and adsorbates. (17-19) Multiple techniques, such as CARS and SERS, can be combined to obtain even stronger signal intensities. (20)

However, SERS is not the only surface-sensitive vibrational spectroscopic technique used in the field of catalysis. For example, other characterization techniques to study surface adsorbates include polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) (21, 22) and sum frequency generation (SFG). (23-25) The latter approach has been pioneered by the group of Somorjai, and has been used, for example, to investigate the hydrogenation of benzene over platinum single crystals with a combined high-pressure scanning tunneling microscopy (HP-STM) and SFG instrument. (26) On the other hand, SERS enables the observation and characterization of the structure of surface species and adsorbates with greater sensitivity up to the level of detecting single molecules. When combined with scanning probe microscopy (SPM) methods, tip-enhanced Raman spectroscopy (TERS) can even reach nanoscale spatial resolution. (27) Furthermore, the SERS substrates can be triggered to start a reaction due to the formation of the strong electric field, hot electrons, and the involved heat generation. (28, 29) With increased control over these SERS substrates, improved Raman signals are obtained with shorter acquisition times, allowing the observation of possible reaction intermediates or even transition states. (30, 31)

A few hurdles need to be overcome before SERS and TERS can become a routine analytical tool for catalysis. In this Perspective, we briefly introduce the capabilities and challenges of SERS and TERS and present several examples of past work and future perspectives to encourage readers to start working with and expand the knowledge of these powerful analytical tools for the study of catalytic reactions. Although this Perspective is mostly aimed at heterogeneous catalysis, it is important to realize that the strengths of SERS are not necessarily limited to this field of research and can also be applied to the field of homogeneous catalysis. (32, 33) Furthermore, SERS is promising to become one of the tools of choice for monitoring the dynamics of biological macromolecules in biomedical applications and is useful for the characterization of biocatalysts, although its current main use is in diagnostics. (34, 35)

SERS. The strong Raman signal enhancement in SERS arises from the excitation of a localized surface plasmon in metallic nanostructures by an external oscillating electric field that matches the resonant frequency of the plasmon. Metallic nanoparticles are polarized by the electric field, and the induced dipole will resonate with the frequency of the incident light. This phenomenon is known as a “localized surface plasmon resonance” (LSPR) and creates a strong localized electromagnetic field, which strongly enhances the Raman signal from analyte molecules in close vicinity of the metallic nanoparticles. The strength of SERS signals dissipates by r^–10 to r^–12, depending on the substrate and analyte. (17-19, 36, 37) This distance dependency makes the technique an ideal surface-specific characterization technique.

SERS substrates are often fabricated from gold and silver nanoparticles. Depending on their size, shape, aggregation state, and the properties of the excitation laser, the Raman signal can be enhanced by over a factor of 10⁶. (17-19, 31, 38) Silver nanoparticles provide stronger SERS signals than gold nanoparticles; however, gold nanoparticles are often preferred because of their higher stability. (39) Indeed, gold nanoparticles are more stable than their silver counterparts and are therefore easier to handle and store. Additionally, they are more likely to retain their SERS activity during experiments requiring elevated temperatures and/or pressures. However, because silver nanoparticles are more SERS active for laser excitation below 600 nm, they provide stronger signal enhancement since Raman scattering intensity is proportional to λ^–4.

The strongest signal enhancements in SERS substrates are obtained from so-called “hot spots”, sites that have the strongest LSPR. For example, at the junction between a nanoparticle with another nanoparticle or a bulk metal surface, the surface plasmons can overlap to form gap-mode plasmons (Figure 1a,b). Depending on the distance between the particles, these gap-mode plasmons tremendously enhance the signal intensity in comparison to single particles, and it vanishes quickly when they move away from each other (Figure 1c–e). (40, 41) This knowledge of hot spots illustrates the difficulty of applying SERS to other catalysts besides silver, gold, and copper. Since the highest enhancements come from between two plasmonic particles, one of the largest challenges becomes the observation of surface species and adsorbates on other catalytic materials.

Figure 1. Strongest EFs arise from hot spots, which are produced by gap-mode plasmons that emerge between closely spaced plasmonic particles or tip–surface interactions where the plasmons overlap. (a) The Raman signal EF can reach theoretical values of 10⁸ for dimer gold nanoparticles under 559 nm laser irradiance (40) and (b) 10¹¹ for a sharp gold tip–gold surface interaction under 633 nm laser irradiance. (40) (c) The electric field is at its strongest when the particles touch and rapidly reduces to a negligible value when the particles are more than 15 nm away from each other. (d) This can be observed in the SERS spectra of adsorbed ammonium salt of pyrene on Ag@SiO₂ spheres. (e) Plot of SERS EF versus distance between the particles. (41) Reprinted with permission from ref 40. Copyright 2008 Royal Society of Chemistry. Reprinted from ref 41. Copyright 2012 American Chemical Society.

Micro- and Nanostructured SERS Surfaces. Nanoparticle-based SERS offers advantages in terms of ease of preparation and control of chemistry, but has limited reproducibility due to surface inhomogeneity, varying dimer orientation, and ill-defined dimer spacing. For over a decade efforts have been made to create SERS surfaces with well-defined and homogeneously distributed hot spots using a variety of methods such as nanoimprinting, e-beam lithography, focused ion beam (FIB) milling, laser interference lithography (LIL), and template-based technologies that are much more promising. (42, 43) Of these methods, photolithography holds great promise because of its exact geometric control and availability of an extensive technological toolbox. With this technique, structures such as nanogroove, nanopyramid, and nanogap–nanowire arrays have been recently realized with tunable gap spacing and high spatially averaged analytical enhancement factors (AEF), (44) as shown in Figure 2. (45, 46) Since in the first two of these approaches LIL is used in combination with anisotropic (100) silicon etching to create nanometer pitches and spacing, no mask is needed and the method is therefore relatively cheap. However, a disadvantage of these anisotropically etched structures is that the SERS hot spots with high signal enhancement occur only at a very small percentage of the surface area because the groove width and spacing between the pyramid sidewalls vary strongly. The third structure, the nanogap–nanowire, is particularly interesting for two reasons. First, the gap size remains constant (<20 nm) as opposed to the groove and pyramid structures, while a large percentage of the surface gives high AEFs. The latter fact is due to the extremely high nanogap density of ∼1000 m·cm^–2. (45) In Figure 2d it is shown that practically all of the 2500 spots measured (at 1068 cm^–1) exhibit AEF values between 1 × 10⁷ and 2 × 10⁷ with an average value of 1.5 × 10⁷. (45) The second advantage of the nanowire–nanogap structure is that it offers the opportunity of combining electrochemical reactions with in situ SERS analysis. Such a spectro-electrochemical technique gives the opportunity to study redox reactions and electron-driven processes in situ and has great importance for the study of catalytic reactions. It has also been shown to be of great value for studying and analyzing adsorbates, chemisorbed species, and reaction intermediates. (47) The nanowires can be contacted electrically in an interdigitated way under potentiostatic control, and finally the nanostructured surface can be integrated in a microfluidic system. For example, such a setup can be utilized to measure the spectral shift of iron bands upon using a Ag/AgCl reference electrode and a platinum counter electrode. It was found that when the redox state of the hemin group of the mercaptopyridine (MPy)/hemin modified gold nanowires was changed by shuttling the voltage between −0.2 V (Figure 2e) and −0.5 V (Figure 2f) versus Ag/AgCl, a corresponding change in the SERS spectra was observed. (48) This demonstrates that a combination of orthogonal analytical techniques combined with dynamic control of environmental conditions using microfluidics clearly holds great promise for in situ study of catalytic reactions.

Figure 2. (a) Nano v-grooves, (46) (b) artist’s impression of nanopyramids, (46) (c) nanowires and nanogaps with cross section in inset, (45) (d) histogram of analytical enhancement factor (AEF) on a nanowire–nanogap substrate, (45) (e) −0.2 V and (f) −0.5 V spectro-electrogram of MPY/hemin modified gold nanowire electrodes with the Fe²⁺ and Fe³⁺ bands indicated. (48) Reprinted from refs 45, 46, and 48. Copyright 2013, 2010, and 2015, respectively, American Chemical Society.

Combining SERS and Catalysis. Gold and silver metal nanoparticles show catalytic behavior in a variety of reactions, implying that they can simultaneously act as sensor as well as catalyst. (49, 50) Gold and silver catalysts can generally be used in three different types of surface reactions: heterogeneous catalysis, (51) electrochemical reactions, (47) and photocatalytic (plasmon-driven) reactions. (52-54)

Valuable industrial reactions, such as NO_x reduction, (55) epoxidation reactions, (50, 56) and methanol synthesis (57) can be carried out over copper and silver metals. However, because of their lower stability in air, they are less implemented in SERS in comparison to gold nanoparticles. Alloys made from silver/gold or copper/gold often have higher stability than pure materials. Gold–silver alloys can be fabricated for example by a simple coreduction of HAuCl₄ and AgNO₃ using trisodium citrate. (58) Star-shaped copper/gold alloys have been prepared as well by a coreduction using glucose as reductant. (59) The introduction of other metals during the synthesis to prepare alloyed nanoparticles not only is interesting to increase the stability, but also will affect the position of the LSPR as well as catalytic activity. (60)

A recent study by Marimuthu et al. showed that the oxidation state of surface atoms in copper nanoparticles can be tuned by light during the epoxidation of propylene. (56) When the LSPR of the metallic core of the particles is excited, the subsequent increased electric field or hot electrons can reduce the copper oxide shell. The threshold light intensity to reduce the copper oxide surface was found to be 550 mW/cm², meaning that Raman lasers can easily be used to reduce the oxide surface. A plasmonic material that can reduce its oxidized surface by using Raman lasers sounds like the ideal SERS substrate. However, although the threshold intensity is far below the laser intensity used in SERS, we are skeptical whether this can be applied for SERS experiments because this mechanism has not been mentioned anywhere else in the literature.

When SERS activity and catalytic activity do not go hand in hand, innovative materials have to be applied. For example, gold nanoparticles become most catalytically active for sizes of approximately 5 nm, (61, 62) whereas particles smaller than roughly 20 nm do not give a significant Raman signal enhancement. (63) Several research groups have devised methods to combine the catalytic activity of small gold nanoparticles with bigger SERS particles. By varying the synthesis conditions of a seeded growth method slightly, 125 nm gold particles were prepared with porous surfaces. These porous surfaces behaved in a similar fashion as sub-5 nm gold nanoparticles, whereas the overall particle provided the plasmonic enhancement for SERS. (64) Other methods describe the use of particles with different exposed facets, (65) adsorbing small gold nanoparticles to gelatin-covered SERS particles, (66) or by adsorption of smaller gold particles to an oxide-coated plasmonic particle. (67)

Model Reactions. One of the most investigated reactions in recent SERS studies is the reduction of 4-nitrothiophenol (4-NTP) to 4-aminothiophenol (4-ATP). (68) Thiol-functionalized molecules, such as 4-NTP and 4-ATP, exhibit high affinity for metal surfaces, guaranteeing their close contact with the SERS substrate. Additionally, the Raman scattering cross section of molecules containing nitro- and amino-functionalized groups in combination with aromatic rings is relatively large, and at certain excitation wavelengths this can lead to resonance Raman scattering. Furthermore, the use of thiols in catalysis gives the possibility of studying the kinetics of surface reactions with only minor interference of diffusion, adsorption, and desorption mechanisms because they are fixed on the surface. The combination of these properties makes 4-ATP and 4-NTP ideal model molecules for SERS experiments.

The reduction of 4-NTP by NaBH₄ requires the presence of a metal catalyst and can be performed at ambient conditions. Consequently, gold and silver nanoparticles meet the requirements for both catalysis and SERS substrate. Various papers and reviews have already been published concerning the reactions of 4-ATP and 4-NTP. (54, 68-73) Model studies using 4-ATP and 4-NTP molecules can be used to increase our understanding of SERS in catalysis and to gain more insight into the interpretation of SERS spectra. Herein, we present several recent examples to demonstrate the possibilities and also the difficulties of interpreting SERS results.

By preparing well-defined particles with different morphologies, it is possible to link structure of a catalyst to its performance. However, it should be kept in mind that SERS activity is strongly dependent on a particle’s size and shape. Since the electric field enhancement is highly local, it is inherent that the probing area of SERS measures only a fraction of the catalytically active surface. For example, Zhang and Wang used gold nanoparticles with different geometries to study their facet-dependent catalytic activity for the reduction of 4-ATP to 4-NTP with SERS. (65) As expected, high-index faceted particles were the most active according to the data obtained by SERS. However, the more anisotropic particles required a much shorter acquisition time for sufficient SERS signal in order to observe clear bands in the spectra, indicating that these particles exhibit intrinsic hot spots. Drawing conclusions about the overall catalytic activity of a particle is therefore difficult with SERS because the Raman signal intensity at hot spots is several orders of magnitude stronger than over the rest of the particle and therefore dominates the overall spectrum. Additional studies, such as ultraviolet–visible (UV–vis) measurements, should then be performed for comparison.

Plasmon-Driven Reactions. SERS cannot simply be used as a noninvasive characterization technique; the plasmonic nanoparticles can interfere with the reaction of interest in multiple ways. (28, 52, 69, 74-76) First, the massive electromagnetic field near the surface can weaken certain bonds in the analyte, initiating reactions. (28) Second, the heat generated as a result of the absorbed light will change the reaction conditions, affecting both temperature (77) and subsequently analyte concentrations. (73-78) Third, the plasmonic particles can generate new and alternative reaction pathways by the formation and injection of hot electrons (Figure 3).

Figure 3. (a) Schematic diagram of the formation of hot electrons and holes in silver nanoparticles, which are able to catalyze both oxidative and reductive reactions. (79) (b) Possible reactions occurring during the chemical reduction of 4-NTP by NaBH₄ over gold nanoparticles. (c) NMF-calculated SERS spectra of the three pure components including their assignment to the three molecular species 4-NTP (blue), 4,4′-DMAB (green), and 4-ATP (red). (98) (d) Raw SERS spectra of the reduction of 4-NTP to 4-ATP over Au/Pt/Au catalysts, including DMAB-associated peaks for intermediate volumes of NaBH₄ added, corresponding to the calculated spectra from panel c. (98) Reprinted with permission from ref 79. Copyright 2012 Royal Society of Chemistry. Reprinted from ref 98. Copyright 2011 American Chemical Society.

Hot electrons can be generated at hot spots, where electrons are excited from below the Fermi level to an occupied state below the vacuum level. When an electron-acceptor is close to the surface, these “hot electrons” can be injected into the lowest unoccupied molecular orbital (LUMO) of this molecule. Simultaneously, the hole can also accept electrons from the highest occupied molecular orbital (HOMO) of a nearby molecule (Figure 3a). (79)

The three alternative pathways can take place simultaneously and can affect each other. These side effects do not mean that SERS is useless for catalysis; however, it does mean that one has to make sure that what is measured is definitely the reaction of interest, and not a SERS artifact. Additionally, the three side effects can be advantageously used to initiate reactions, for example by extreme heating of the sample by applying pulsed lasers.

One has to make sure that what is measured is definitely the reaction of interest and not a SERS artifact.

The use of plasmonic materials as catalysts has recently become a growing field within photocatalysis because it can produce chemicals with alternative pathways at ambient temperatures. Because both the reaction and the SERS signal are the strongest at hot spots, SERS seems to be an ideal method to study plasmon-driven reactions. (71) Photocatalysts are useful as wastewater treatment and as a sustainable energy-supplier for the future, (80) and plasmon-driven catalysis is an exciting field in its own right. Interested readers are therefore directed to the recent literature. (28, 54, 69, 76)

To study conventional catalysts, one has to make sure that the characterization technique does not interfere with the reaction of interest. Decreasing laser energy and power and changing the polarization are known to affect the catalytic power of the plasmons, although the signal-enhancing effects of the plasmonic particles are thereby sacrificed. (29, 72, 81)

Borrowing SERS Activity. Because SERS is limited to a few materials, (82-84) SERS activity has to be “borrowed” from existing substrates when the catalyst itself is not SERS active. (85) Catalytically active nanoparticles can be directly assembled on a SERS substrate. Joseph et al., for example, reported a novel method to study the reduction of 4-NTP to 4-ATP over platinum catalysts. (33) The SERS signal of 4-NTP was used to obtain kinetic data of the reaction in solution. The 2 nm platinum particles were either randomly deposited over a SERS substrate consisting of gold nanoparticles or were used in colloidal solution. Since the reaction data of immobilized particles was not significantly different from the colloidal catalyst, the reaction mechanism is thought to be the same; thus, this method of immobilizing catalyst nanoparticles can possibly be applied to other chemical reactions as well. (33) However, this method does not give information exclusive to the platinum-catalyzed reaction because the gold particles are not entirely inert nor are they isolated.

Postsynthesis mixing of separately prepared Au and Pt NPs can result in a heterogeneous distribution of different particles throughout the sample. To guarantee close contact between sensor and catalyst, thin overlayers of catalytically active metal can be sputtered over existing SERS substrates. For example, Heck et al. (86) prepared gold nanoshells with submonolayer coverages of palladium and observed improved activity for the aqueous-phase hydrodechlorination of dichloroethylene (DCE). These nanostructures allowed for the detection of the dechlorination of 1,1-DCE to ethane. Although the signal intensity of the probe molecule 4-ATP was reduced after palladium was grown on the gold nanoshells, the signal intensities of adsorbed 1,1-DCE increased, indicating the stronger interaction of 1,1-DCE to Pd. The dechlorination at the surface was observed by the appearance of peaks associated with Cl–M and C–M bonds. Additionally, a range of intermediate structures from 1,1-DCE to ethane were detected. (86)

Core–shell nanoparticles can be fabricated by colloidal synthesis as well. (85) Using this method, any direct interaction with the plasmonic particle can be prevented when a uniform coating is applied. A crucial side effect can take place when thin metal layers are deposited over other metals. Due to the formation of alloys or by electron transfer from the core to the shell, the electronic structure of the catalyst may change, influencing its activity. (87) It has been reported that it is necessary to keep the metal coatings at least 5 monolayers thick so that it behaves as a “pure” material. (88) Attard et al. have used a colloidal method to produce platinum-coated SERS particles for studying the effect of surface poisoning on the alkyne adsorption on platinum catalysts. (89)

Because SERS substrates are heterogeneous by definition, the materials will have to be cleverly designed for homogeneous catalysis depending on the desired results. To increase the signal of low concentrated catalysts, reactants, and products, the materials can be simply mixed in solution. (33) However, when these materials show a negative affinity to the SERS substrates, insufficient signal will be obtained and no conclusive spectrum can be formed. Additionally, some molecules in the solution might have a higher affinity to gold or silver (also depending on the facets), increasing the chance to observe them and simultaneously decreasing the chance to observe other molecules. Similar to heterogeneous catalysis, the catalysts are preferred to be fixed to the surface of a well-defined SERS substrate so that we know what we are looking at. Other methods are to fix the catalysts to a self-assembled monolayer (SAM) on a gold substrate or to induce aggregation between the nanoparticles by introducing the catalyst. (34, 35, 90)

SHINERS, for Stable and Noninvasive Characterization. A promising method to minimize plasmonic side-reactions is isolating the noble metal nanoparticles using thin dielectric oxide coatings. Coatings of <10 nm thick silica have been proposed to make plasmonic particles inert. (91) The technique, quite aptly named “shell-isolated nanoparticle-enhanced Raman spectroscopy” (SHINERS), has been successfully applied, among others, to study catalysts. (67, 91-93) Coating of nanoparticles with oxides enhances their stability in demanding conditions and increases their shelf life. Al₂O₃ shells of less than 1 nm thick can enhance the stability of the nanoparticles to withstand temperatures of up to 500 °C under nitrogen for a few hours (Figure 4d,e). (94) The improved stability makes SHINERS a highly promising technique to study a wide variety of heterogeneous catalysts. Shell-isolated nanoparticles (SHINs) can be used for expanding the SERS activity to other materials because the oxide coating reduces plasmon-driven reactions (Figure 4a) and increases the stability of the plasmonic particle (Figure 4c,d).

Figure 4. Advantages of SHINs over bare gold nanoparticles. (a) SHINs prevent plasmon-driven reactions. SERS spectra collected from 4-ATP adsorbed on 80 nm gold particles, 80 nm gold nanoparticles covered with 5 nm gold particles, and 80 nm SHINs covered with 5 nm gold particles. DMAB is not observed when SHINs are implemented. (67) Adapted from ref 67. Copyright 2013 American Chemical Society. (b) SERS EF calculated for a variety of silver nanocubes: bare (I, red) and SiO₂-coated cubes using different methods (II–V, blue). All SiO₂-coated nanocubes show increased EFs compared to bare silver nanocubes. (99) Adapted with permission from ref 99. Copyright 2015 Royal Society of Chemistry. (c) UV–vis absorption spectra of gold nanoparticles at elevated temperatures indicate that their LSPR shifts above temperatures of 100 °C. (94) (d) UV–vis absorption spectra of gold nanoparticles coated with 1 nm alumina at elevated temperatures indicate that stability is maintained up to 400 °C. (94) Adapted from ref 94. Copyright 2007 American Chemical Society. (e) SHINs (green) could potentially serve as a support for many other catalysts (purple spheres). Because the electric field is stronger (red) at the surface of the SHIN, it is expected that the catalyst–support interface can be characterized.

An effective method to implement SHINERS in catalysis is to prepare a physical mixture of bulk catalyst material with SHINs. Such a strategy was used by Li et al. to study nickel-based solid oxide fuel cell (SOFC) anodes. Spherical silver nanoparticles were coated with 10 nm thick silica layers to increase their thermal stability, enabling them to withstand temperatures of up to 500 °C. However, due to the thickness of the coating the Raman signal was enhanced only by a factor of 150. Even with this low EF, the authors were able to observe surface species in ceria (CeO₂) at elevated temperatures and detect small quantities of coke that lay beneath the sensitivity limit of conventional Raman spectroscopy. Li et al. state that this technique can be readily applied to other catalytic and electrochemical systems, and we feel similarly. This method is highly suitable for the detection of surface species and adsorbates and could show even greater potential when more stable and/or thinner coatings can be produced. (92, 93)

The oxide layer can furthermore serve as a support material for nanoparticles (Figure 4e), facilitating close contact between the SERS-active particle and the catalyst. (67, 96, 97) Similarly to other studies concerning the reduction of 4-NTP to 4-ATP, (64, 65, 98) Xie et al. observed DMAB as intermediate when the large plasmonic particles were not coated with silica. (67) However, when the large particle was isolated by an ultrathin (∼1.5 nm) but nonporous silica coating, the bands associated with DMAB were no longer observed and only the reduction of 4-NTP to 4-ATP was detected (Figure 4a). Gold catalysts of 5 and 10 nm deposited on the silica layer were used to show that smaller particles were indeed more effective catalysts.

A similar approach was applied by Attard et al. where they used silica-coated gold nanoparticles on single-crystal platinum surfaces to observe adsorbates with SHINERS, and more recently during the hydrogenation of ethyl pyruvate (EP) to (R)-ethyl lactate (EL) over modified and unmodified Pt{hkl} electrodes. (89, 95) SHINs deposited on different platinum surfaces proved to noninvasively enhance the signal of EP adsorbed to the surface. An intermediate structure of the ethyl pyruvate, more specifically a half-hydrogenation state (HHS), was formed by addition of a hydrogen atom to the keto carbonyl group; in addition, a new species was identified as intact chemisorbed EP bound in a μ₂(C,O) configuration, as illustrated in Figure 5 with a series of SHINERS spectra, as well as for the calculated structures of Pt-chemisorbed EP and HHS. (95) The relative ratio of both species was sensitive to the Pt surface structure. More specifically, the μ₂(C,O) EP surface species was dominant at pristine Pt{111} and Pt{100} surfaces, whereas the HHS was observed only at surfaces with defects and kinks, such as Pt{110} and roughened Pt electrodes.

Figure 5. (a, b) SHINERS spectra of Pt{*hkl*} single crystals immersed in 0.1 M EP/0.1 M HClO₄ recorded under hydrogen evolution conditions (−0.1 V). (c) Schematic depiction of the half-hydrogenated state (HHS) intermediate. (d) Calculated structure of EP adsorbed in the μ₂(C,O) configuration. (e) Calculated structure of HHS at a Pt{221} surface. Reprinted from ref 95. Copyright 2016 American Chemical Society.

In our lab, the dimerization of 4-ATP over pinhole-free SHINs was observed, contradicting the previously mentioned experiments. (70) This indicates that in the research conducted by Xie et al. the rate of plasmon-driven reactions is most likely slowed significantly by the SiO₂ coating in comparison to the reduction by NaBH₄, making the observation of DMAB impossible. (67) In many publications, side effects are reported to be caused by hot electrons injected into nearby molecules, but we believe that the extremely strong electric field facilitates photosensitive reactions as well. (28) Although SERS intensity can increase for some coated particles (Figure 4b), (99) increasing thickness of oxide coatings will result in a decrease of the signal-enhancing effect and prevent side reactions caused by hot electrons or a strong electric field.

Any catalyst can potentially be assembled on the surface of SHINs, allowing the observation of Raman active surface species on these catalysts. These particles can then be tuned in size, shape, and structure to characterize the effect on the reaction, similar to the method described by Xie et al. (67) One could also make use of different oxide (91, 100, 101) or carbon (102) coatings to mimic the support material, although some combinations of materials are effective photocatalysts, such as titania-coated gold nanoparticles. (74, 100) A coating of several nanometers separates the catalyst particle and the plasmonic particle, meaning that for increasing catalyst size, the signal intensity decreases dramatically for the far side of the particle (Figure 4e). The strongest signals are produced at the metal–support interface in comparison to the far side of the particle. This effect can be exploited by attaching larger catalysts to the surface, making it more likely to observe reactions or catalyst structures at the support–catalyst interface. (103)

Tip-Enhanced Raman Spectroscopy. To directly relate catalytic activity with the morphology of catalysts, we need to map and monitor catalytic activity on a single catalytic particle. Instruments with high sensitivity and above all nanoscale spatial resolution are required to reach this goal. (104) Therefore, a more direct method to correlate catalyst structure to activity is by combining high chemical sensitivity of SERS with nanoscale spatial resolution of scanning probe microscopy. To showcase the possibilities of the AFM–Raman methodology, the catalytic activity of silver nanocubes in rhodamine 6G degradation was linked to their distribution. (105) However, the diffraction-limited spatial resolution of Raman spectroscopy (typically 200–300 nm) is not overcome by combining SERS and AFM.

The spatial resolution can be significantly improved when a metal-coated tip is implemented; this technique is referred to as TERS. (106) Compared to SERS where hot spots are randomly distributed over the substrate, the electromagnetic enhancement in TERS occurs only at a single point of the TERS tip-apex, which can be scanned over a surface using sensitive SPM feedback to make a nanoscale map of surface chemistry and catalytic activity simultaneously with the topography. TERS improves the diffraction-limited spatial resolution of confocal Raman spectroscopy to the nanoscale, with a recent breakthrough reaching the subnanometer regime with STM-based TERS demonstrating the capability of TERS to map even single molecules. (27)

The potential of TERS for in situ catalysis research was first demonstrated by Domke and Pettinger (107) who studied the organometallic catalyst cobalt meso-tetraphenylporphyrin (CoTPP) on Au(111) substrate using STM-TERS with a Au tip. With TERS, the authors could spectroscopically discriminate between axially complexed and ligand-free CoTPP regions on the Ag substrate and identify chemical species complexed with CoTPP. TERS spectra from well-ordered CoTPP regions identified in the STM topography images showed vibrational bands characteristic of linker-modified CoTPP sandwiched between two Au layers, whereas TERS spectra from the disordered region showed vibrational features of CoTPP axially complexed with CO and NO formed by catalytic reduction of CO₂ and NO₂ from ambient air. This study demonstrates that TERS can be successfully used to correlate structure with catalytic activity in heterogeneous catalysis, while the observation of such complexes indicates possible applications in homogeneous catalysis.

Studying Light-Triggered Reactions with TERS. TERS studies of the plasmon-driven photocatalytic reaction (4-NTP to DMAB) was carried out for the first time in a collaborative effort by Weckhuysen and Deckert et al. (29) The reaction was triggered using a 532 nm laser and was unobtrusively monitored using a 633 nm laser. It was found that a complete self-assembled monolayer (SAM) is necessary to obtain a stable starting signal as the molecules in an incomplete monolayer can change their orientation or move in and out of the sampling area more easily. (29) Because TERS measures only a small number of molecules and spectra are not averaged over an ensemble, signal intensities are highly influenced by small fluctuations of analyte molecules in the measured area. (108) Time-series Raman spectra measured before and after the reaction at the tip-apex clearly showed the Raman bands associated with 4-NTP decrease and DMAB increase in intensity over time. This demonstrates the potential of TERS to monitor reactions on single catalytic particles over time. (29) Almost simultaneously, Zhang, Xu, and co-workers (109) performed a similar experiment using high-vacuum (HV) STM-TERS to demonstrate that this photocatalytic reaction is driven by hot electrons produced during surface plasmon resonance. The authors showed that the reaction can be controlled by plasmon intensity, which depends on laser power or the tip–substrate distance. In an additional report it was shown using HV STM-TERS that the reaction was indeed the result of the plasmon resonance in the nanogap between a Au tip and a Ag substrate and any thermal effects could be neglected. (110)

Very recently, the potential of TERS to actually relate catalyst structure to activity was realized by Kumar et al. with AFM-based TERS. (111) The activity of silver nanoparticles was studied using the plasmon-driven photocatalytic dimerization of 4-ATP to DMAB. The authors first mapped the reaction at a single point of contact of the Ag-coated TERS tip with a reactant substrate. Since both the silver particles and the silver-coated tip were catalytically active in the reaction 4-ATP to DMAB, the tip was made inert by applying a 3–5 nm thick Al₂O₃ coating while preserving its plasmonic enhancement. Using such an alumina-protected TERS tip, the authors were able to map catalytically active sites on the Ag substrate with 20 nm spatial resolution, as shown in Figure 6. (111)

Figure 6. (a) AFM topography image of the Ag catalyst substrate. (b) TERS map of the area marked by the dashed rectangle in panel a showing signal intensities of a DMAB-associated band at 1142 cm^–1. (c) Near-field spectra measured at the positions marked in panel b. (d) Intensity profile along the dotted line marked in panel b showing the spatial resolution of the TERS map using a fitted Gaussian curve (red) to be 20 nm. (111) Reprinted with permission from ref 111. Copyright 2015 Royal Society of Chemistry.

We believe that dielectric coating of TERS tips is a good strategy for obtaining reliable and stable data during measurements, similarly to the application of SHINERS. It is known that the tips can be contaminated by surface species, causing additional bands in the spectrum or worse, the loss of their signal-enhancing properties. (112) Dielectric coatings such as oxides can prevent adsorption of contaminants or irreversible tip damage from oxidative reactions, thereby enhancing their stability. However, because the decay length of TERS near-field is only a few nanometers, (113) a thick dielectric coating may significantly decrease the plasmonic enhancement of the TERS tip. (37) Therefore, the thickness of the protective dielectric coating should not be more than a few nanometers (ideally 1–2 nm) and should be pinhole-free for TERS tips to provide Raman signal enhancements. Alternatively, aluminum-coated tips have been used in TERS in combination with a 363.8 nm ultraviolet laser. (114) Because aluminum is known to form a thin native oxide layer of approximately 3 nm, such tips are expected to be chemically more stable, although higher-energy lasers are required that may cause degradation of chemical species. (82)

The sensitivity of TERS measurements can be significantly enhanced by utilizing the plasmonic coupling of a metal or metal-coated tip with a metal substrate. Using this so-called “gap-mode” TERS, extremely high EFs can be reached. For example, gold-coated tips close to metallic substrates can produce Raman signals that are a factor of 10³ stronger than those of tips close to dielectric substrates, such as SiO₂. (115) However, care must be taken to ensure that the metal used for the tip or substrate is not catalytically active for the reaction under study. So far, TERS has been mainly used for the study of plasmon-driven photocatalytic reactions in which the reactants and products have a rather large Raman cross section. However, the reactants and products employed in more industrially relevant catalytic reactions usually have a much lower Raman cross section. Furthermore, such reactions are carried out at temperatures and pressures much higher than ambient conditions. Therefore, TERS probes with high plasmonic enhancement, stability, and lifetime are required to make TERS a powerful tool for the study of catalytic reactions under operating conditions.

Toward the Observation of Single Molecules. Spectral fluctuations that arise in TERS and SERS experiments do not have to be an undesired result but can be a topic of interest as well. Shifts in the band position can give clues to the mechanism of a reaction. Not only do orientational effects become more visible when homogeneous broadening is reduced by measuring smaller ensembles, but also other interesting events can be observed as well. For example, one can distinguish between isotopes because vibrational energy levels are related to the reduced mass of the participating atoms. (116)

Isotopes can be useful for the study of catalytic reactions and have been implemented to reveal a variety of reaction mechanisms using techniques such as steady-state isotopic transient kinetic analysis (SSITKA). (117) However, this technique observes only the product and is not able to detect the surface species and adsorbates. Combining SERS with SSITKA could enable the characterization of surface species and possibly track the changes in the spectrum of the adsorbed molecules when it reacts with the isotopes. We believe this can provide crucial information about the specific reaction mechanisms.

Time-resolved Raman spectroscopy should be combined with TERS to give a spatial resolution in the nanometer scale and a temporal resolution in the picosecond scale.

Additionally, the chance to find short-lived species such as intermediates should increase when approaching single-molecule experiments. Knowing which and how many intermediates are present during the reaction is crucial to optimally tune the catalyst as it will tell us the amount of rate-limiting steps and how to possibly improve the reaction kinetics. Combining single-particle and single-molecule kinetic studies have been performed in fluorescence microscopy experiments, revealing intermediates and interparticle heterogeneities such as size-dependent activity. (118) However, fluorescence microscopy experiments do not enable the observation of structures of the reactants and requires the use of fluorescent reactants or products, thereby limiting its use. SERS, on the other hand, can supply us with structural information on both the reactant and catalyst and can be applied to a wider range of molecules, allowing a larger versatility.

To approach single-molecule experiments, the analytes can be diluted. However, dilution of the reactants cannot always be applied to obtain reaction mechanisms. Reaction conditions will often change upon dilution, and this can lead to different reaction pathways. For example, the dimerization of 4-NTP cannot proceed for single molecules, and it was expected that the reaction would therefore be inhibited. Zhang et al. found that a plasmon-driven reaction of highly diluted 4-NTP still takes place, although the diazo-product is not formed. (75) When there is no second molecule nearby, the nitro-group is split from the substrate and thiophene (TP) is obtained as the product. Hot electrons generated at the hot spots were proposed to have sufficient energy to excite 4-NTP to a transient negative ion. The negative ion “travels” to the excited state of TP and returns to the ground state of TP, returning the electron to the gold surface. (75)

Single or several molecules at hot spots can dominate the spectrum over larger ensembles because the electric field is significantly stronger than for molecules positioned at other structures. If a reaction takes place while the molecule is situated at the hot spot, we should be able to observe the reaction. Plasmonic catalysts therefore prove to be an ideal substrate for SERS experiments, because both the high signal enhancement and catalytic activity originate from the hot spot. (28, 54) Previous research performed in our group utilized this principle to study the dimerization of 4-NTP to DMAB. (29, 30, 119) Chemometric methods were applied to obtain a clearer image of the kinetics during the reaction, demonstrated in Figure 7. (30) First, a one-component principal-component analysis (PCA) removed the spectral blinking from the data and already resulted in a lower signal-to-noise ratio (Figure 7 left panel vs middle panel). After removal of the spectral blinking, the reaction spectra were taken through a two-component multivariate curve resolution (MCR) that described the reactant and the product. This resulted in a better understanding of the reaction data with a lower signal-to-noise ratio. The spectra that were removed from the kinetic data were subsequently analyzed with a four-component MCR analysis (Figure 7, right side). Two of the components were similar to the two main components in the kinetic data, apart from some slight variations in peak intensities that were caused by differences in orientation. The third and fourth components were low in intensity over the measured time, apart from two single instances for each component. The third component resembled much of DMAB, but the fourth component is a completely unknown structure and is a potential reaction intermediate. (30)

Figure 7. PCA used to obtain kinetic data with reduced noise in SERS experiments. (Left) The conventional method to obtain kinetic data is to plot a peak area over time. (Middle) Spectral fluctuations can be removed from the spectrum with a PCA time filter, after which a two-component MCR can further clear up the kinetic data. The kinetic data is now analyzed over full spectra instead of over single peaks, making it less prone to shifts in band positions. (Right) The discarded data after the PCA time filter can be analyzed with MCR to find possible intermediate structures. (30) Adapted with permission from ref 30. Copyright 2015 Wiley-VCH.

Ultrafast Raman Spectroscopy, Watching a Molecule Breathe. Most Raman spectrometers require spectral integration times of at least a second and are therefore not fit to observe short-lived species such as intermediates. Recent progress made in the field of ultrafast Raman spectroscopy allows acquisition times in the order of picoseconds with Raman line widths of tens of reciprocal centimeters. (31) Such fast acquisition times enable the elucidation of a great deal of reaction steps and dynamics, such as bond forming and breaking. To extend the potential of time-resolved Raman spectroscopy, it can be combined with other techniques such as CARS, to improve the signal intensity, and SERS, to increase the signal intensity even further to detect surface species. (120) (121)

Because the technique generates extremely large electric fields that can potentially damage the sample and the SERS antennae, the experiments need to be performed in a highly controlled environment. Yampolsky et al. managed to reduce the damage to SERS-antennae by encapsulating gold dimers and adsorbed trans-1,2-bis(4-pyridyl) ethylene (BPE) in a thick porous silica shell of about 70–80 nm. (120) The hot spots between the dimer in combination with CARS provided excellent signal enhancement for the observation of BPE near the single-molecule level. By applying a femtosecond laser scanning CARS microscope and by tuning the frequencies of the pump and the Stokes pulses, the authors were able to observe an oscillating signal that was associated with the quantum beating of the closely spaced excited vibrational modes of BPE. It is important to note that a single time trace was not obtained instantly, but the result was obtained after averaging the signal over an hour. (120)

Ultrafast Raman spectroscopy can lead to promising results where one could actually follow bond formation and breaking. However, the technique suffers from the possibility of sample damage and requires highly controlled environments and thus does not seem fit for the characterization of catalysts in their operating conditions yet. Ultimately, time-resolved Raman spectroscopy should be combined with TERS to give a spatial resolution in the nanometer scale and a temporal resolution in the picosecond scale. However, such experiments have to be performed on fixed analytes under ultrahigh vacuum to prevent signal blinking and signal degradation.

Challenges and Future Prospects. Based on the above considerations it should be clear that SERS and TERS can make the difference in three specific fields. The first field concerns the monitoring of chemical reactions at the molecular level, including the potential to identify reaction intermediates and even transition states. Second, the use of SERS in combination with its plasmonic platform opens up ample opportunities to conduct a wealth of chemical reactions at the surface of gold and silver, which are known to be catalytically active. The third field is associated with the heat developed by the plasmonic materials upon illumination providing new opportunities to locally create the proper experimental conditions to trigger a catalytic reaction.

The heat developed by the plasmonic materials upon illumination provides new opportunities to locally create the proper experimental conditions to trigger a catalytic reaction.

It is important to realize that SERS and TERS have made tremendous progress over recent years and are becoming mature spectroscopic techniques. Improvements in substrate preparation have made SERS more robust and sensitive, opening the path for the detection of surface species with low Raman scattering cross sections in a wide range of reaction conditions. We believe that, following the highlighted examples in this perspective article, SERS can become an attractive and versatile characterization method for a wide variety of catalytic materials. However, this will not be a simple task and requires highly interdisciplinary research for developing stable and inert SERS substrates, without losing plasmonic enhancement. Simple spherical plasmonic nanoparticles often do not suffice for heterogeneous catalysis research because their enhancement signal is negligible when they are not in an aggregated state. (122) Dimers or other structures, such as nanorods, are expected to give better results with respect to signal enhancement, but they are currently less stable. It is believed that SERS substrates prepared by photolithography can yield more robust and homogeneous signal intensities. Similarly, TERS tips, especially with Ag-coating, are known to degrade at a fast rate and require development of robust methods of thin, pinhole free protective dielectric coatings for prolonged measurements in ambient and especially at operating conditions of catalysts.

Creating stronger LSPRs will result in more intense Raman signal intensities but can also lead to undesired effects, such as substrate damage and unwanted side-reactions. More research effort is needed to study the role of the strong localized electromagnetic field and local heating and if ultrathin oxide layers are really able to prevent plasmonic side-reactions.

We believe that SHINERS and its TERS counterpart can play significant roles in the study of heterogeneous catalysis. SHINs have been proven to be more inert and stable than bare particles and can even act as a support material, guaranteeing close contact between catalyst and sensor for heterogeneous catalysis (Table 1). Additionally, alumina-protected TERS tips have proven to be a useful, stable, and noninvasive technique for mapping catalytic activity of silver photocatalysts. Combining the current developments in SERS and TERS with other developments in Raman, such as CARS and ultrafast spectroscopy, will most likely lead to useful mechanistic information regarding catalytic solids.

Table 1. Overview of Different SERS Substrates Including Their Advantages and Disadvantages

Author Information

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Corresponding Author
- Bert M. Weckhuysen - Faculty of Science, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands; Email: [email protected]
Authors
- Thomas Hartman - Faculty of Science, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands
- Caterina S. Wondergem - Faculty of Science, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands
- Naresh Kumar - Faculty of Science, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands; National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, U.K.
- Albert van den Berg - BIOS Lab on a Chip Group and MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
Notes
The authors declare no competing financial interest.

Biographies

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Thomas Hartman obtained his M.Sc. degree in Nanomaterials: Chemistry and Physics from Utrecht University in 2014. He is now working under the guidance of Prof. Bert Weckhuysen as a Ph.D. student to increase the understanding of operating catalysts with SERS by implementing oxide-coated plasmonic nanoparticles as catalyst support material and SERS substrates.

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Caterina S. Wondergem obtained her M.Sc. degree in Nanomaterials: Chemistry and Physics from Utrecht University. She graduated cum laude in 2014 with a thesis entitled “The Effect of Water on Methanol-to-Olefins Reactions Studied by Advanced In-situ Microspectroscopy”. Later that year she started her Ph.D. research “Unravelling the Mysteries of Solar Steam Nanobubbles” under the supervision of Prof. Bert Weckhuysen.

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Naresh Kumar obtained his B.Tech. from the Indian Institute of Technology Delhi. He received his Master Degree in Physics from King’s College London, where he worked on the nanoscale chemical imaging of polymer-blend thin films using TERS. Naresh has now set up an AFM-TERS system and has applied it to solve various problems at National Physical Laboratory. He started his Ph.D. research in 2015 under the supervision of Prof. Bert Weckhuysen.

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Albert van den Berg was appointed as full professor on Miniaturized Systems for (Bio)Chemical Analysis at the University of Twente in 2000. His current research interests focus on microanalysis systems and nanosensors; nanofluidics; and single cells, tissues, and organs on chips, especially with applications in personalized health care, drug development, and development of sustainable (nano-)technologies.

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Bert M. Weckhuysen has been a full professor in Inorganic Chemistry and Catalysis at Utrecht University since 2000. His research interests are in the development of spectroscopy and microscopy techniques for elucidating the working and deactivation principles of catalytic solids, mostly applied under true reaction conditions.

Acknowledgment

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B.M.W. acknowledges financial support from The Netherlands Organisation for Scientific Research (NWO) Gravitation Program (Netherlands Center for Multiscale Catalytic Energy Conversion, MCEC) and a European Research Council (ERC) Advanced Grant (321140). N.K. acknowledges funding from the ‘NanoSpec’ project in the Strategic Capability programme of the National Measurements System of the U.K. Department of Business, Innovation and Skills.

References

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Wachs, Israel E.; Roberts, Charles A.
Chemical Society Reviews (2010), 39 (12), 5002-5017CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
A review. The mol. aspect of the Raman vibrational selection rules allows for the mol. structural and reactivity detns. of metal oxide catalytic active sites in all types of oxide catalyst systems (supported metal oxides, zeolites, layered hydroxides, polyoxometalates (POMs), bulk pure metal oxides, bulk mixed oxides and mixed oxide solid solns.). The mol. structural and reactivity detns. of metal oxide catalytic active sites are greatly facilitated by the use of isotopically labeled mols. The ability of Raman spectroscopy to (i) operate in all phases (liq., solid, gas and their mixts.), (ii) operate over a very wide temp. (-273 to >1000°) and pressure (UHV to »100 atm) range, and (iii) provide mol. level information about metal oxides makes Raman spectroscopy the most informative characterization technique for understanding the mol. structure and surface chem. of the catalytic active sites present in metal oxide heterogeneous catalysts. The recent use of hyphenated Raman spectroscopy instrumentation (e.g., Raman-IR, Raman-UV-vis, Raman-EPR) and the operando Raman spectroscopy methodol. (e.g., Raman-MS and Raman-GC) is allowing for the establishment of direct structure-activity/selectivity relationships that will have a significant impact on catalysis science in this decade. Consequently, this crit. review will show the growth in the use of Raman spectroscopy in heterogeneous catalysis research, for metal oxides as well as metals, is poised to continue to exponentially grow in the coming years.
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Bañares, M. A.; Mestl, G. Structural Characterization of Operating Catalysts by Raman Spectroscopy Adv. Catal. 2009, 52, 43– 128 DOI: 10.1016/S0360-0564(08)00002-3
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Cheng, J.-X.; Xie, X. S. Coherent Anti-Stokes Raman Scattering Microscopy: Instrumentations, Theory and Applications J. Phys. Chem. B 2004, 108, 827– 840 DOI: 10.1021/jp035693v
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Smith, E.; Dent, G. Modern Raman Spectroscopy—A Practical Approach, 1st ed.; John Wiley & Sons, Ltd: Chichester, England, 2005.
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Schlücker, S. Surface-Enhanced Raman Spectroscopy: Concepts and Chemical Applications Angew. Chem., Int. Ed. 2014, 53, 4756– 4795 DOI: 10.1002/anie.201205748
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Surface-Enhanced Raman Spectroscopy: Concepts and Chemical Applications
Schluecker, Sebastian
Angewandte Chemie, International Edition (2014), 53 (19), 4756-4795CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
A review. Surface-enhanced Raman scattering (SERS) has become a mature vibrational spectroscopic technique during the last decades and the no. of applications in the chem., material, and in particular life sciences is rapidly increasing. This Review explains the basic theory of SERS in a brief tutorial and-based on original results from recent research-summarizes fundamental aspects necessary for understanding SERS and provides examples for the prepn. of plasmonic nanostructures for SERS. Chem. applications of SERS are the centerpiece of this Review. They cover a broad range of topics such as catalysis and spectroelectrochem., single-mol. detection, and (bio)anal. chem.
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Tian, Z. Q.; Ren, B.; Wu, D. Y. Surface-Enhanced Raman Scattering: From Nobel to Transition Metals and From Rough Surfaces to Ordered Nanostructures J. Phys. Chem. B 2002, 106, 9463– 9483 DOI: 10.1021/jp0257449
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Xie, W.; Schlücker, S. Rationally Designed Multifunctional Plasmonic Nanostructures for Surface-Enhanced Raman Spectroscopy: A Review Rep. Prog. Phys. 2014, 77, 116502 DOI: 10.1088/0034-4885/77/11/116502
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Rationally designed multifunctional plasmonic nanostructures for surface-enhanced Raman spectroscopy: a review
Xie, Wei; Schluecker, Sebastian
Reports on Progress in Physics (2014), 77 (11), 116502/1-116502/22CODEN: RPPHAG; ISSN:0034-4885. (IOP Publishing Ltd.)
Rationally designed multifunctional plasmonic nanostructures efficiently integrate two or more functionalities into a single entity, for example, with both plasmonic and catalytic activity. This review article is focused on their synthesis and use in surface-enhanced Raman scattering (SERS) as a mol. spectroscopic technique with high sensitivity, fingerprint specificity, and surface selectivity. After a short tutorial on the fundamentals of Raman scattering and SERS in particular, applications ranging from chem. (heterogeneous catalysis) to biol. and medicine (diagnostics/imaging, therapy) are summarized.
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Zhang, Y.; Zhen, Y.-R.; Neumann, O.; Day, J. K.; Nordlander, P.; Halas, N. J. Coherent Anti-Stokes Raman Scattering with Single-Molecule Sensitivity Using a Plasmonic Fano Resonance Nat. Commun. 2014, 5, 4424 DOI: 10.1038/ncomms5424
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Coherent anti-Stokes Raman scattering with single-molecule sensitivity using a plasmonic Fano resonance
Zhang, Yu; Zhen, Yu-Rong; Neumann, Oara; Day, Jared K.; Nordlander, Peter; Halas, Naomi J.
Nature Communications (2014), 5 (), 4424CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
Plasmonic nanostructures are of particular interest as substrates for the spectroscopic detection and identification of individual mols. Single-mol. sensitivity Raman detection has been achieved by combining resonant mol. excitation with large electromagnetic field enhancements experienced by a mol. assocd. with an interparticle junction. Detection of mols. with extremely small Raman cross-sections (∼10-30 cm2 sr-1), however, has remained elusive. Here we show that coherent anti-Stokes Raman spectroscopy (CARS), a nonlinear spectroscopy of great utility and potential for mol. sensing, can be used to obtain single-mol. detection sensitivity, by exploiting the unique light harvesting properties of plasmonic Fano resonances. The CARS signal is enhanced by ∼11 orders of magnitude relative to spontaneous Raman scattering, enabling the detection of single mols., which is verified using a statistically rigorous bi-analyte method. This approach combines unprecedented single-mol. spectral sensitivity with plasmonic substrates that can be fabricated using top-down lithog. strategies.
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Hoffmann, F. M. Infrared Reflection-Absorption Spectroscopy of Adsorbed Molecules Surf. Sci. Rep. 1983, 3, 107– 192 DOI: 10.1016/0167-5729(83)90001-8
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Infrared reflection-absorption spectroscopy of adsorbed molecules
Hoffmann, Friedrich M.
Surface Science Reports (1983), 3 (2-3), 107-92CODEN: SSREDI; ISSN:0167-5729.
A review with 202 refs.
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Rupprechter, G. Sum Frequency Generation and Polarization-Modulation Infared Reflection Absorption Spectrosocpy of Functioning Model Catalysts from Ultrahigh Vacuum to Ambient Pressure Adv. Catal. 2007, 51, 133– 263 DOI: 10.1016/S0360-0564(06)51004-1
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Shen, Y. R. Surface Properties Probed by Second-Harmonic and Sum-Frequency Generation Nature 1989, 337, 519– 525 DOI: 10.1038/337519a0
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Surface properties probed by second-harmonic and sum-frequency generation
Shen, Y. R.
Nature (London, United Kingdom) (1989), 337 (6207), 519-25CODEN: NATUAS; ISSN:0028-0836.
A review on optical 2nd-harmonic generation and IR-visible light sum-frequency generation studies of surfaces and interfaces. Combined with ultrashort laser pulses, these methods can be used to study surface dynamics and reactions with subpicosecond time resoln. Sixty-one refs.
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Han, H. L.; Melaet, G.; Alayoglu, S.; Somorjai, G. A. In-situ Microscopy and Spectroscopy Applied to Surfaces at Work ChemCatChem 2015, 7, 3625– 3628 DOI: 10.1002/cctc.201500642
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Somorjai, G. A.; Frei, H.; Park, J. Y. Advancing the Frontiers in Nanocatalysis, Biointerfaces and Renewable Energy Conversion by Innovations of Surface Techniques J. Am. Chem. Soc. 2009, 131, 16589– 16605 DOI: 10.1021/ja9061954
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Bratlie, K. M.; Montano, M. O.; Flores, L. D.; Paajanen, M.; Somorjai, G. A. Sum Frequency Generation Vibrational Spectroscopic and High-Pressure Scanning Tunneling Microscopic Studies of Benzene Hydrogenation on Pt(111) J. Am. Chem. Soc. 2006, 128, 12810– 12816 DOI: 10.1021/ja0626032
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Sum Frequency Generation Vibrational Spectroscopic and High-Pressure Scanning Tunneling Microscopic Studies of Benzene Hydrogenation on Pt(111)
Bratlie, Kaitlin M.; Montano, Max O.; Flores, Lucio D.; Paajanen, Matti; Somorjai, Gabor A.
Journal of the American Chemical Society (2006), 128 (39), 12810-12816CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Sum frequency generation (SFG) vibrational spectroscopy and high-pressure scanning tunneling microscopy (HP-STM) have been used in combination for the first time to study a catalytic reaction. These techniques have been able to identify surface intermediates in situ during benzene hydrogenation on a Pt(111) single-crystal surface at Torr pressures. In a background of 10 Torr of benzene, STM is able to image small ordered regions corresponding to the c(2√3 × 3)rect structure in which each mol. is chemisorbed at a bridge site. In addn., individual benzene mols. are also obsd. between the ordered regions. These individual mols. are assumed to be physisorbed benzene on the basis of the SFG results showing both chemisorbed and physisorbed mols. The surface becomes too mobile to image upon addn. of hydrogen but is detd. to have physisorbed and chemisorbed benzene present by SFG. It was spectroscopically detd. that heating the platinum surface after poisoning with CO displaces benzene mols. The high-coverage pure CO structure of (√19 × √19)R23.4° imaged with STM is a verification of spectroscopic measurements.
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Zhang, R.; Zhang, Y.; Dong, Z. C.; Jiang, S.; Zhang, C.; Chen, L. G.; Zhang, L.; Liao, Y.; Aizpurua, J.; Luo, Y. Chemical Mapping of a Single Molecule by Plasmon-Enhanced Raman Scattering Nature 2013, 498, 82– 86 DOI: 10.1038/nature12151
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Chemical mapping of a single molecule by plasmon-enhanced Raman scattering
Zhang, R.; Zhang, Y.; Dong, Z. C.; Jiang, S.; Zhang, C.; Chen, L. G.; Zhang, L.; Liao, Y.; Aizpurua, J.; Luo, Y.; Yang, J. L.; Hou, J. G.
Nature (London, United Kingdom) (2013), 498 (7452), 82-86CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
Visualizing individual mols. with chem. recognition is a longstanding target in catalysis, mol. nanotechnol. and biotechnol. Mol. vibrations provide a valuable fingerprint' for such identification. Vibrational spectroscopy based on tip-enhanced Raman scattering allows us to access the spectral signals of mol. species very efficiently via the strong localized plasmonic fields produced at the tip apex. However, the best spatial resoln. of the tip-enhanced Raman scattering imaging is still limited to 3-15 nm, which is not adequate for resolving a single mol. chem. Here we demonstrate Raman spectral imaging with spatial resoln. below one nanometer, resolving the inner structure and surface configuration of a single mol. This is achieved by spectrally matching the resonance of the nanocavity plasmon to the mol. vibronic transitions, particularly the downward transition responsible for the emission of Raman photons. This matching is made possible by the extremely precise tuning capability provided by scanning tunneling microscopy. Exptl. evidence suggests that the highly confined and broadband nature of the nanocavity plasmon field in the tunnelling gap is essential for ultrahigh-resoln. imaging through the generation of an efficient double-resonance enhancement for both Raman excitation and Raman emission. Our technique not only allows for chem. imaging at the single-mol. level, but also offers a new way to study the optical processes and photochem. of a single mol.
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Long, R.; Li, Y.; Song, L.; Xiong, Y. Coupling Solar Energy into Reactions: Materials Design for Surface Plasmon-Mediated Catalysis Small 2015, 11, 3873– 3889 DOI: 10.1002/smll.201403777
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Coupling Solar Energy into Reactions: Materials Design for Surface Plasmon-Mediated Catalysis
Long, Ran; Li, Yu; Song, Li; Xiong, Yujie
Small (2015), 11 (32), 3873-3889CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
A review. Enabled by surface plasmons, noble metal nanostructures can interact with and harvest incident light. As such, they may serve as unique media to generate heat, supply energetic electrons, and provide strong local electromagnetic fields for chem. reactions through different mechanisms. This solar-to-chem. pathway provides a new approach to solar energy use, alternative to conventional semiconductor-based photocatalysis. To provide readers with a clear picture of this newly recognized process, this review presents coupling solar energy into chem. reactions through plasmonic nanostructures. It starts with a brief introduction of surface plasmons in metallic nanostructures, followed by a demonstration of tuning plasmonic features by tailoring their phys. parameters. Owing to their tunable plasmonic properties, metallic materials offer a platform to trigger and drive chem. reactions at the nanoscale, as systematically overviewed. The design rules for plasmonic materials for catalytic applications are further outlined based on existing examples. At the end of this article, the challenges and opportunities for further development of plasmonic-mediated catalysis toward energy and environmental applications are discussed.
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van Schrojenstein Lantman, E. M.; Deckert-Gaudig, T.; Mank, A. J. G.; Deckert, V.; Weckhuysen, B. M. Catalytic Processes Monitored at the Nanoscale with Tip-Enhanced Raman Spectroscopy Nat. Nanotechnol. 2012, 7, 583– 586 DOI: 10.1038/nnano.2012.131
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Catalytic processes monitored at the nanoscale with tip-enhanced Raman spectroscopy
van Schrojenstein Lantman, Evelien M.; Deckert-Gaudig, Tanja; Mank, Arjan J. G.; Deckert, Volker; Weckhuysen, Bert M.
Nature Nanotechnology (2012), 7 (9), 583-586CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
Heterogeneous catalysts play a pivotal role in the chem. industry, but acquiring mol. insights into functioning catalysts remains a significant challenge. Recent advances in micro-spectroscopic approaches have allowed spatiotemporal information to be obtained on the dynamics of single active sites and the diffusion of single mols. However, these methods lack nanometer-scale spatial resoln. and/or require the use of fluorescent labels. Here, we show that time-resolved tip-enhanced Raman spectroscopy can monitor photocatalytic reactions at the nanoscale. We use a silver-coated at. force microscope tip to both enhance the Raman signal and to act as the catalyst. The tip is placed in contact with a self-assembled monolayer of p-nitrothiophenol mols. adsorbed on gold nanoplates. A photocatalytic redn. process is induced at the apex of the tip with green laser light, while red laser light is used to monitor the transformation process during the reaction. This dual-wavelength approach can also be used to observe other mol. effects such as monolayer diffusion.
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van Schrojenstein Lantman, E. M.; de Peinder, P.; Mank, A. J. G.; Weckhuysen, B. M. Separation of Time-Resolved Phenomena in Surface-Enhanced Raman Scattering of the Photocatalytic Reduction of p-Nitrothiophenol ChemPhysChem 2015, 16, 547– 554 DOI: 10.1002/cphc.201402709
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Separation of Time-Resolved Phenomena in Surface-Enhanced Raman Scattering of the Photocatalytic Reduction of p-Nitrothiophenol
van Schrojenstein Lantman, E. M.; de Peinder, P.; Mank, A. J. G.; Weckhuysen, B. M.
ChemPhysChem (2015), 16 (3), 547-554CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
Straightforward anal. of chem. processes on the nanoscale is difficult, as the measurement vol. is linked to a discrete no. of mols., ruling out any ensemble averaging over rotation and diffusion processes. Raman spectroscopy is sufficiently selective for monitoring chem. changes, but is not sufficiently sensitive to be applied directly. Surface-enhanced Raman spectroscopy (SERS) can be applied for studying reaction kinetics, but adds addnl. variability in the signal as the enhancement factor is not the same for every location. A novel chemometric method described here separates reaction kinetics from short-term variability, based on the lack of fit in a principal-component anal. We show that it is possible to study effects that occur on different time scales independently without data redn. using the photocatalytic redn. of p-nitrothiophenol as a showcase system. Using this approach a better description of the nanoscale reaction kinetics becomes available, while the short-term variations can be examd. sep. to examine reorientation and/or diffusion effects. It may even be possible to identify reaction intermediates through this approach. With only a limited no. of reactive mols. in the studied vol., an intermediate on a SERS hot spot may temporarily dominate the spectrum. Now such events can be easily sepd. from the bulk conversion process by making use of this chemometric method.
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Keller, E. L.; Brandt, N. C.; Cassabaum, A. A.; Frontiera, R. R. Ultrafast Surface-Enhanced Raman Spectroscopy Analyst 2015, 140, 4922– 4931 DOI: 10.1039/C5AN00869G
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Ultrafast surface-enhanced Raman spectroscopy
Keller, Emily L.; Brandt, Nathaniel C.; Cassabaum, Alyssa A.; Frontiera, Renee R.
Analyst (Cambridge, United Kingdom) (2015), 140 (15), 4922-4931CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)
A review. Ultrafast surface-enhanced Raman spectroscopy (SERS) with pico- and femtosecond time resoln. has the ability to elucidate the mechanisms by which plasmons mediate chem. reactions. Here the authors review three important technol. advances in these new methodologies, and discuss their prospects for applications in areas including plasmon-induced chem. and sensing at very low limits of detection. Surface enhancement, arising from plasmonic materials, was successfully incorporated with stimulated Raman techniques such as femtosecond stimulated Raman spectroscopy (FSRS) and coherent anti-Stokes Raman spectroscopy (CARS). These techniques are capable of time-resolved measurement on the femtosecond and picosecond time scale and can be used to follow the dynamics of mols. reacting near plasmonic surfaces. The potential application of ultrafast SERS techniques to probe plasmon-mediated processes, such as H2 dissocn. and solar steam prodn. are discussed. Addnl., the possibilities for high sensitivity SERS sensing using these stimulated Raman spectroscopies are discussed.
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Hu, K.; Li, D.; Cui, J.; Cao, Y.; Long, Y. In Situ Monitoring of Palladacycle-Mediated Carbonylation by Surface-Enhanced Raman Spectroscopy RSC Adv. 2015, 5, 97734– 97737 DOI: 10.1039/C5RA20292B
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In situ monitoring of palladacycle-mediated carbonylation by surface-enhanced Raman spectroscopy
Hu, Kai; Li, Da-Wei; Cui, Jing; Cao, Yue; Long, Yi-Tao
RSC Advances (2015), 5 (118), 97734-97737CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
Palladium-catalyzed carbonylation has emerged as one of the most potential approaches for the synthesis of carbonyl-contg. mols., however, the understanding remains challenging in many reactions partly because of a lack of robust monitoring methods. Herein, authors report a novel surface-enhanced Raman spectroscopy (SERS) based strategy for the in situ monitoring of palladacycle-mediated carbonylation. The nanoplatforms integrated with SERS activity and reaction mediability were constructed through assembling new synthesized palladacycles (PCs) on the surface of gold nanoparticles. It was shown that, when carbon monoxide (CO) was introduced to the nanoplatform-contg. system as a C1 source, palladacycle-mediated carbonylation was initiated, and the SERS spectra of the nanoplatforms changed concomitantly. With this SERS spectrum variation, the reaction mechanism could be investigated facilely, and the corresponding reaction was found to follow a pseudo-first-order kinetics rate law based on the relationship between the relative ratiometric peak intensities of I1319/I1338 and the reaction time. Therefore, using the proposed SERS approach, the carbonylation process could be directly monitored in situ without tedious pretreatments.
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Joseph, V.; Engelbrekt, C.; Zhang, J.; Gernert, U.; Ulstrup, J.; Kneipp, J. Characterizing the Kinetics of Nanoparticle-Catalyzed Reactions by Surface-Enhanced Raman Scattering Angew. Chem., Int. Ed. 2012, 51, 7592– 7596 DOI: 10.1002/anie.201203526
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Characterizing the Kinetics of Nanoparticle-Catalyzed Reactions by Surface-Enhanced Raman Scattering
Joseph, Virginia; Engelbrekt, Christian; Zhang, Jingdong; Gernert, Ulrich; Ulstrup, Jens; Kneipp, Janina
Angewandte Chemie, International Edition (2012), 51 (30), 7592-7596, S7592/1-S7592/4CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
We demonstrate that SERS can be used to study directly the kinetics of a catalytic reaction in situ. Our approach is novel by allowing the structural characterization of the reactant and product surface species in the reaction as well as investigating rate consts. in the same expt. This was possible by using sep. gold and platinum nanoparticles that were simultaneously attached to the same glass surface. Our method is independent of the optical absorption properties of the reaction products and/or the catalysts.
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Cialla, D.; Pollok, S.; Steinbrücker, C.; Weber, K.; Popp, J. SERS-Based Detection of Biomolecules Nanophotonics 2014, 3, 383– 411 DOI: 10.1515/nanoph-2013-0024
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SERS-based detection of biomolecules
Cialla, Dana; Pollok, Sibyll; Steinbruecker, Carolin; Weber, Karina; Popp, Juergen; Perelman, Lev T.
Nanophotonics (2014), 3 (6), 383-411CODEN: NANOLP; ISSN:2192-8614. (Walter de Gruyter GmbH)
A review. In order to detect biomols., different approaches using for instance biol., spectroscopic or imaging techniques were established. Due to the broad variety of these methods, this review is focused on surface enhanced Raman spectroscopy (SERS) as an anal. tool in biomol. detection. Here, the mol. specificity of Raman spectroscopy is combined with metallic nanoparticles as sensor platform, which enhances the signal intensity by several orders of magnitude. Within this article, the characterization of diverse biomols. by SERS is explained and moreover current application fields are presented. The SERS intensity and as a consequence thereof the reliable detection of the biomol. of interest is affected by distance, orientation and affinity of the mol. towards the metal surface. Furthermore, the great capability of the SERS technique for cutting-edge applications like pathogen detection and cancer diagnosis is highlighted. The authors wish to motivate by this comprehensive and crit. summary researchers from various scientific background to create their own ideas and schemes for a SERS-based detection and anal. of biomols.
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Peng, F.; Su, Y. Y.; Zhong, Y. L.; Fan, C. H.; Lee, S. T.; He, Y. Silicon Nanomaterials Platform for Bioimaging, Biosensing, and Cancer Therapy Acc. Chem. Res. 2014, 47, 612– 623 DOI: 10.1021/ar400221g
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Silicon Nanomaterials Platform for Bioimaging, Biosensing, and Cancer Therapy
Peng, Fei; Su, Yuanyuan; Zhong, Yiling; Fan, Chunhai; Lee, Shuit-Tong; He, Yao
Accounts of Chemical Research (2014), 47 (2), 612-623CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
A review. Silicon nanomaterials are an important class of nanomaterials with great potential for technologies including energy, catalysis, and biotechnol., because of their many unique properties, including biocompatibility, abundance, and unique electronic, optical, and mech. properties, among others. Silicon nanomaterials are known to have little or no toxicity due to favorable biocompatibility of silicon, which is an important precondition for biol. and biomedical applications. In addn., huge surface-to-vol. ratios of silicon nanomaterials are responsible for their unique optical, mech., or electronic properties, which offer exciting opportunities for design of high-performance silicon-based functional nanoprobes, nanosensors, and nanoagents for biol. anal. and detection and disease treatment. Moreover, silicon is the second most abundant element (after oxygen) on earth, providing plentiful and inexpensive resources for large-scale and low-cost prepn. of silicon nanomaterials for practical applications. Because of these attractive traits, and in parallel with a growing interest in their design and synthesis, silicon nanomaterials are extensively investigated for wide-ranging applications, including energy, catalysis, optoelectronics, and biol. Among them, bioapplications of silicon nanomaterials are of particular interest. In the past decade, scientists have made an extensive effort to construct a silicon nanomaterials platform for various biol. and biomedical applications, such as biosensors, bioimaging, and cancer treatment, as new and powerful tools for disease diagnosis and therapy. Nonetheless, there are few review articles covering these important and promising achievements to promote the awareness of development of silicon nanobiotechnol. In this Account, we summarize recent representative works to highlight the recent developments of silicon functional nanomaterials for a new, powerful platform for biol. and biomedical applications, including biosensor, bioimaging, and cancer therapy. First, we show that the interesting photoluminescence properties (e.g., strong fluorescence and robust photostability) and excellent biocompatibility of silicon nanoparticles (SiNPs) are superbly suitable for direct and long-term visualization of biol. systems. The strongly fluorescent SiNPs are highly effective for bioimaging applications, esp. for long-term cellular labeling, cancer cell detection, and tumor imaging in vitro and in vivo with high sensitivity. Next, we discuss the utilization of silicon nanomaterials to construct high-performance biosensors, such as silicon-based field-effect transistors (FET) and surface-enhanced Raman scattering (SERS) sensors, which hold great promise for ultrasensitive and selective detection of biol. species (e.g., DNA and protein). Then, we introduce recent exciting research findings on the applications of silicon nanomaterials for cancer therapy with encouraging therapeutic outcomes. Lastly, we highlight the major challenges and promises in this field, and the prospect of a new nanobiotechnol. platform based on silicon nanomaterials.
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Pettinger, B. Single-Molecule Surface- and Tip-Enhanced Raman Spectroscopy Mol. Phys. 2010, 108, 2039– 2059 DOI: 10.1080/00268976.2010.506891
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Dieringer, J. A.; Mcfarland, A. D.; Shah, N. C.; Stuart, D. A.; Whitney, A. V.; Yonzon, C. R.; Young, M. A.; Zhang, X.; Van Duyne, R. P. Surface Enhanced Raman Spectroscopy: New Materials, Concepts, Characterization Tools, and Applications Faraday Discuss. 2006, 132, 9– 26 DOI: 10.1039/B513431P
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Surface enhanced Raman spectroscopy: new materials, concepts, characterization tools, and applications
Dieringer, Jon A.; McFarland, Adam D.; Shah, Nilam C.; Stuart, Douglas A.; Whitney, Alyson V.; Yonzon, Chanda R.; Young, Matthew A.; Zhang, Xiaoyu; Van Duyne, Richard P.
Faraday Discussions (2006), 132 (Surface Enhanced Raman Spectroscopy), 9-26CODEN: FDISE6; ISSN:1359-6640. (Royal Society of Chemistry)
Surface-enhanced Raman spectroscopy (SERS) is currently experiencing a renaissance in its development driven by the remarkable discovery of single mol. SERS (SMSERS) and the explosion of interest in nanophotonics and plasmonics. Because excitation of the localized surface plasmon resonance (LSPR) of a nanostructured surface or nanoparticle lies at the heart of SERS, it is important to control all of the factors influencing the LSPR to maximize signal strength and ensure reproducibility. These factors include material, size, shape, interparticle spacing, and dielec. environment. All of these factors must be carefully controlled to ensure that the incident laser light maximally excites the LSPR in a reproducible manner. This article describes the use of nanosphere lithog. for the fabrication of highly reproducible and robust SERS substrates for both fundamental studies and applications. At. layer deposition (ALD) is introduced as a novel fabrication method for dielec. spacers to study the SERS distance dependence and control the nanoscale dielec. environment. Wavelength scanned SER excitation spectroscopy (WS SERES) measurements show that enhancement factors ∼108 are obtainable from NSL-fabricated surfaces and provide new insight into the electromagnetic-field enhancement mechanism. Tip-enhanced Raman spectroscopy (TERS) is an extremely promising new development to improve the generality and information content of SERS. A 2-dimensional correlation anal. is applied to SMSERS data. Finally, the 1st in vivo SERS glucose sensing study is presented.
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Moskovits, M. Persistent Misconceptions Regarding SERS Phys. Chem. Chem. Phys. 2013, 15, 5301– 5311 DOI: 10.1039/c2cp44030j
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Persistent misconceptions regarding SERS
Moskovits, Martin
Physical Chemistry Chemical Physics (2013), 15 (15), 5301-5311CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
SERS is some 35 years old, and the subject of over 11 000 articles. The field of Plasmonics, and large aspects of Metamaterials are clearly based on concepts that became current as a result of SERS. Despite this, a no. of persistent, fuzzy ideas about the origin of the enhancement in SERS continue to be current even among SERS researchers, leading to the external impression that SERS is uniquely poorly understood. Six such ideas are discussed.
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Etchegoin, P. G.; Le Ru, E. C. Basic Electromagnetic Theory of SERS. In Surface Enhanced Raman Spectroscopy: Analytical, Biophysical and Life Science Applications; Schlücker, S., Ed.; Wiley-VCH: Weinheim, 2010; pp 1– 37.
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Etchegoin, P. G.; Le Ru, E. C. A Perspective on Single Molecule SERS: Current Status and Future Challenges Phys. Chem. Chem. Phys. 2008, 10, 6079– 6089 DOI: 10.1039/b809196j
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A perspective on single molecule SERS: current status and future challenges
Etchegoin, P. G.; Le Ru, E. C.
Physical Chemistry Chemical Physics (2008), 10 (40), 6079-6089CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
A review in presented of a some of the basic principles underlying current research in single-mol. surface-enhanced Raman scattering (SM-SERS). The authors summarize, by the same token, conditions and characteristics that are common to most SM-SERS conditions, and discuss their implications for the understanding of data and for the comparison among different methods. The authors try to emphasize aspects of the problem that are not conventionally discussed in detail in the literature. In particular, the authors provide a full length discussion on the topics of: (i) the min. SERS enhancement necessary to observe a single mol., and (ii) the spatial distribution of the enhancement factor (EF) around hot-spots (which affects the statistics of SM-SERS events). A brief outlook into future perspectives of the different techniques used in SM-SERS and a few outstanding questions are also provided.
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Shanthil, M.; Thomas, R.; Swathi, R. S.; Thomas, K. G. Ag@SiO₂ Core–Shell Nanostructures: Distance-Dependent Plasmon Coupling and SERS Investigation J. Phys. Chem. Lett. 2012, 3, 1459– 1464 DOI: 10.1021/jz3004014
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Ag@SiO2 Core-Shell Nanostructures: Distance-Dependent Plasmon Coupling and SERS Investigation
Shanthil, M.; Thomas, Reshmi; Swathi, R. S.; Thomas, K. George
Journal of Physical Chemistry Letters (2012), 3 (11), 1459-1464CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
Enhancement of Raman signals of pyrene due to the enhanced elec. fields on the surface of silver nanoparticles has been investigated by controlling the thickness of the silica shell. Dimeric nanostructures having well-defined gaps between two silver nanoparticles were prepd., and the gap size (d) was varied from 1.5 to 40 nm. The mols. trapped at the dimeric junctions showed higher Raman signal enhancements when the gap was less than 15 nm due to the presence of amplified elec. field, in agreement with our theor. studies. The exptl. Raman enhancement factors at the hot spots follow a 1/dn dependence, with n = 1.5, in agreement with the recent theor. studies by Schatz and co-workers. Exptl. results presented here on the distance dependence of surface enhanced Raman spectroscopy (SERS) enhancement at the hot spots can provide insight on the design of newer plasmonic nanostructures with optimal nanogaps.
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Stewart, M. E.; Anderton, C. R.; Thompson, L. B.; Maria, J.; Gray, S. K.; Rogers, J. A.; Nuzzo, R. G. Nanostructured Plasmonic Sensors Chem. Rev. 2008, 108, 494– 521 DOI: 10.1021/cr068126n
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Nanostructured plasmonic sensors
Stewart, Matthew E.; Anderton, Christopher R.; Thompson, Lucas B.; Maria, Joana; Gray, Stephen K.; Rogers, John A.; Nuzzo, Ralph G.
Chemical Reviews (Washington, DC, United States) (2008), 108 (2), 494-521CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
A review. Theor. considerations on optical properties of metal nanoparticles and nanoholes, synthesis and fabrication of plasmonic nanostructures, and applications of plasmonic nanostructures in sensing and chem. imaging are discussed.
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Fan, M.; Andrade, G. F. S.; Brolo, A. G. A Review on the Fabrication of Substrates for Surface Enhanced Raman Spectroscopy and Their Applications in Analytical Chemistry Anal. Chim. Acta 2011, 693, 7– 25 DOI: 10.1016/j.aca.2011.03.002
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A review on the fabrication of substrates for surface enhanced Raman spectroscopy and their applications in analytical chemistry
Fan, Meikun; Andrade, Gustavo F. S.; Brolo, Alexandre G.
Analytica Chimica Acta (2011), 693 (1-2), 7-25CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)
A review. This work reviews different types of substrates used for surface-enhanced Raman scattering (SERS) that were developed in the last 10 years. The different techniques of self-assembly to immobilize metallic nanoparticles on solid support are covered. An overview of SERS platforms developed using nanolithog. methods, including electron-beam (e-beam) lithog. and focused ion beam (FIB) milling are also included, together with several examples of template-based methodologies to generate metallic nano-patterns. The potential of SERS to impact several aspects of anal. chem. is demonstrated by selected examples of applications in electrochem., biosensing, environmental anal., and remote sensing. This review shows that highly enhancing SERS substrates with a high degree of reliability and reproducibility can now be fabricated at relative low cost, indicating that SERS may finally realize its full potential as a very sensitive tool for routine anal. applications.
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The magnitude of the SERS enhancement is often described by the term “enhancement factor” (EF). It is a theoretical number that can be calculated with multiple methods. Each gives certain advantages over the others. Two examples of the methods to calculate EFs are the substrate EF (EF) and the analytical AEF (AEF), which are calculated as
$EF = \frac{I_{SERS} / N_{Sur}}{I_{RS} / N_{Vol}}$
where I_SERS is the intensity of the signal under SERS conditions, N_sur the amount of molecules adsorbed on the substrates surface in the spot size of the incident laser, I_RS the average intensity of the signal during normal Raman spectroscopy, and N_vol the average number of molecules in the volume probed by normal Raman spectroscopy.
$AEF = \frac{I_{SERS} / c_{SERS}}{I_{RS} / c_{RS}}$
where c_SERS is the concentration of analyte under SERS conditions. For details, we refer to the pioneering work of Felidj and co-workers:
Felidj, N.; Aubard, J.; Levi, G.; Krenn, J. R.; Salerno, M.; Schider, G.; Lamprecht, P.; Leitner, A.; Aussenegg, F. R. Controlling the Optical Response of Regular Arrays of Gold Particles for Surface-Enhanced Raman Scattering Phys. Rev. B: Condens. Matter Mater. Phys. 2002, 65, 075419 DOI: 10.1103/PhysRevB.65.075419
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Ngoc, L. L. T.; Jin, M.; Wiedemair, J.; van den Berg, A.; Carlen, E. T. Large Area Metal Nanowire Arrays with Tunable Sub-20 Nm Nanogaps ACS Nano 2013, 7, 5223– 5234 DOI: 10.1021/nn4009559
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Jin, M.; Pully, V.; Otto, C.; van den Berg, A.; Carlen, E. T. High-Density Periodic Arrays of Self-Aligned Subwavelength Nanopyramids for Surface-Enhanced Raman Spectroscopy J. Phys. Chem. C 2010, 114, 21953– 21959 DOI: 10.1021/jp106245a
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High-Density Periodic Arrays of Self-Aligned Subwavelength Nanopyramids for Surface-Enhanced Raman Spectroscopy
Jin, Mingliang; Pully, Vishnu; Otto, Cees; van den Berg, Albert; Carlen, Edwin T.
Journal of Physical Chemistry C (2010), 114 (50), 21953-21959CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
Novel nanotextured surfaces are presented with periodically self-aligned subwavelength nanogroove and nanopyramid structures with precisely defined pitch λg that are closely packed with 2 nm sepn. gaps over large areas and form high-d. arrays of hot-spot scattering sites ideally suited for surface-enhanced Raman scattering (SERS) and Raman spectroscopy. The simple self-aligning fabrication technique requires only a single lithog. step and wet anisotropic etching. Measured av. Raman enhancement factors of G ≈ 106 from rhodamine 6G (R6G) on patterned Au surfaces with λg = 200 nm are consistent with numerical calcns. The nanostructured surfaces can be scaled to smaller dimensions, which results in increased enhancement as well as increased hot-spot spatial d.
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Wu, D.-Y.; Li, J.-F.; Ren, B.; Tian, Z.-Q. Electrochemical Surface-Enhanced Raman Spectroscopy of Nanostructures Chem. Soc. Rev. 2008, 37, 1025– 1041 DOI: 10.1039/b707872m
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Electrochemical surface-enhanced Raman spectroscopy of nanostructures
Wu, De-Yin; Li, Jian-Feng; Ren, Bin; Tian, Zhong-Qun
Chemical Society Reviews (2008), 37 (5), 1025-1041CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
A review. This tutorial review 1st describes the early history of SERS as the 1st SERS spectra were obtained from an electrochem. cell, which led to the discovery of the SERS effect in mid-1970s. Up to date, over 500 papers were published on various aspects of SERS from electrochem. systems. The authors then highlight important features of electrochem. SERS (EC-SERS). There are 2 distinctively different properties of elec. fields, the electromagnetic field and static electrochem. field, coexisting in electrochem. systems with various nanostructures. Both chem. and phys. enhancements can be influenced to some extent by applying an electrode potential, which makes EC-SERS one of the most complicated systems in SERS. Great efforts were made to comprehensively understand SERS and analyze EC-SERS spectra from the chem. and phys. enhancement mechanisms to provide meaningful information for revealing the mechanisms of electrochem. adsorption and reaction. The EC-SERS expts. and applications are then discussed from prepn. of nanostructured electrodes to study of SERS mechanisms and from characterization of adsorption configuration to elucidation of electrochem. reaction mechanisms. Finally, prospective developments of EC-SERS in substrates, methods and theory are discussed.
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Yuan, T.; Ngoc, L. L. T.; van Nieuwkasteele, J.; Odijk, M.; van den Berg, A.; Permentier, H.; Bischoff, R.; Carlen, E. T. In Situ Surface-Enhanced Raman Spectroelectrochemical Analysis System with a Hemin Modified Nanostructured Gold Surface Anal. Chem. 2015, 87, 2588– 2592 DOI: 10.1021/ac504136j
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In Situ Surface-Enhanced Raman Spectroelectrochemical Analysis System with a Hemin Modified Nanostructured Gold Surface
Yuan, Tao; Le Thi Ngoc, Loan; van Nieuwkasteele, Jan; Odijk, Mathieu; van den Berg, Albert; Permentier, Hjalmar; Bischoff, Rainer; Carlen, Edwin T.
Analytical Chemistry (Washington, DC, United States) (2015), 87 (5), 2588-2592CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
An integrated surface-enhanced Raman scattering (SERS) spectroelectrochem. (SEC) anal. system is presented that combines a small vol. microfluidic sample chamber (<100 μL) with a compact three-electrode configuration for in situ surface-enhanced Raman spectroelectrochem. The SEC system includes a nanostructured Au surface that serves dual roles as the electrochem. working electrode (WE) and SERS substrate, a microfabricated Pt counter electrode (CE), and an external Ag/AgCl ref. electrode (RE). The nanostructured Au WE enables highly sensitive in situ SERS spectroscopy through large and reproducible SERS enhancements, which eliminates the need for resonant wavelength matching of the laser excitation source with the electronic absorption of the target mol. The new SEC anal. system has the merits of wide applicability to target mols., small sample vol., and a low detection limit. We demonstrate in situ SERS spectroelectrochem. measurements of the metalloporphyrin hemin showing shifts of the iron oxidn. marker band ν4 with the nanostructured Au working electrode under precise potential control.
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McBreen, P. H.; Moskovits, M. A Surface-Enhanced Interacting Raman Study of Ethylene and Oxygen with Supported Silver Catalysts J. Catal. 1987, 103, 188– 199 DOI: 10.1016/0021-9517(87)90105-9
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Boghosian, S.; Bebelis, S.; Vayenas, C. G.; Papatheodorou, G. N. In Situ High Temperature SERS Study of Ag Catalysts Electrodes during Ethylene Epoxidation J. Catal. 1989, 117, 561– 565 DOI: 10.1016/0021-9517(89)90366-7
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Mikami, Y.; Dhakshinamoorthy, A.; Alvaro, M.; García, H. Catalytic Activity of Unsupported Gold Nanoparticles Catal. Sci. Technol. 2013, 3, 58– 69 DOI: 10.1039/C2CY20068F
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Catalytic activity of unsupported gold nanoparticles
Mikami, Yusuke; Dhakshinamoorthy, Amarajothi; Alvaro, Mercedes; Garcia, Hermenegildo
Catalysis Science & Technology (2013), 3 (1), 58-69CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
A review. This article reviews some of the compelling evidence showing that colloidal gold nanoparticles without any solid support exhibit intrinsic catalytic activity for some of the typical gold-catalyzed reactions including CO oxidn., aerobic oxidn. of alcs. and diols, borohydride redns., and carbon-carbon cross coupling reaction among other reactions. A crit. view of the state-of-the-art indicating open issues such as the role of the nature and concn. of the ligand and the possibility of prepg. colloidal samples with preferential crystallog. planes is provided.
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Christopher, P.; Xin, H.; Linic, S. Visible-Light-Enhanced Catalytic Oxidation Reactions on Plasmonic Silver Nanostructures Nat. Chem. 2011, 3, 467– 472 DOI: 10.1038/nchem.1032
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Visible-light-enhanced catalytic oxidation reactions on plasmonic silver nanostructures
Christopher, Phillip; Xin, Hongliang; Linic, Suljo
Nature Chemistry (2011), 3 (6), 467-472CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)
Catalysis plays a crit. role in chem. conversion, energy prodn. and pollution mitigation. High activation barriers assocd. with rate-limiting elementary steps require most com. heterogeneous catalytic reactions to be run at relatively high temps., which compromises energy efficiency and the long-term stability of the catalyst. Here we show that plasmonic nanostructures of silver can concurrently use low-intensity visible light (on the order of solar intensity) and thermal energy to drive catalytic oxidn. reactions-such as ethylene epoxidn., CO oxidn., and NH3 oxidn.-at lower temps. than their conventional counterparts that use only thermal stimulus. Based on kinetic isotope expts. and d. functional calcns., we postulate that excited plasmons on the silver surface act to populate O2 antibonding orbitals and so form a transient neg.-ion state, which thereby facilitates the rate-limiting O2-dissocn. reaction. The results could assist the design of catalytic processes that are more energy efficient and robust than current processes.
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Dorain, P. B.; Von Raben, K. U.; Chang, R. K.; Laube, B. L. Catalytic Formation of SO₃^2- and SO₄^2- from SO₂ on Silver Observed by Surface-Enhanced Raman Scattering Chem. Phys. Lett. 1981, 84, 405– 409 DOI: 10.1016/0009-2614(81)80373-9
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Zhang, Z.; Deckert-Gaudig, T.; Deckert, V. Label-Free Monitoring of Plasmonic Catalysis at the Nanoscale Analyst 2015, 140, 4325– 4335 DOI: 10.1039/C5AN00630A
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Bethke, K. A.; Kung, H. H. Supported Ag Catalysts for the Lean Reduction of NO with C₃H₆ J. Catal. 1997, 172, 93– 102 DOI: 10.1006/jcat.1997.1794
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Supported Ag catalysts for the lean reduction of NO with C3H6
Bethke, K. A.; Kung, H. H.
Journal of Catalysis (1997), 172 (1), 93-102CODEN: JCTLA5; ISSN:0021-9517. (Academic Press)
The activities of 2 and 6 wt% Ag/Al2O3 catalysts for lean NO redn. with C3H6 were compared. High conversions of NO to N2 were obtained over 2 wt% Ag/Al2O3. In contrast, the NO conversions to N2 were much lower over 6 wt% Ag/Al2O3, and this catalyst formed a substantial amt. of N2O. The difference in the behavior of the two catalysts was attributed to the much higher Ag dispersion for the 2 wt% than the 6 wt% sample, such that the oxidn. states of Ag were different under reaction conditions. The 2 wt% Ag/Al2O3 was believed to contain silver in the +1 oxidn. state under reaction conditions, while the 6 wt% Ag/Al2O3 catalyst contained Ag0 particles, the amt. of which decreased at higher temps. The presence of Ag0 resulted in a high rate of C3H6 combustion at the expense of NOx redn. A synergistic effect was obsd. over a mixt. of Al2O3 and 2 or 6 wt% Ag/Al2O3 and was attributed to the transfer of a very short-lived intermediate from Al2O3 to Ag/Al2O3 or vice versa.
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Marimuthu, A.; Zhang, J.; Linic, S. Tuning Selectivity in Propylene Epoxidation by Plasmon Mediated Photo-Switching of Cu Oxidation State Science 2013, 339, 1590– 1593 DOI: 10.1126/science.1231631
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Tuning Selectivity in Propylene Epoxidation by Plasmon Mediated Photo-Switching of Cu Oxidation State
Marimuthu, Andiappan; Zhang, Jianwen; Linic, Suljo
Science (Washington, DC, United States) (2013), 339 (6127), 1590-1593CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
Oxidn. of functioning copper has restricted its applicability as a catalyst for com. important epoxidn. of propylene to form propylene oxide. Here, we report that steady-state selectivity in propylene epoxidn. on copper (Cu) nanoparticles increases sharply when the catalyst is illuminated with visible light. The selectivity increase is accompanied by light-induced redn. of the surface Cu atoms, which is brought about by photoexcitation of the localized surface plasmon resonance (LSPR) of Cu. We discuss multiple mechanisms by which Cu LSPR weakens the Cu-O bonds, reducing Cu2O.
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Karelovic, A.; Ruiz, P. The Role of Copper Particle Size in Low Pressure Methanol Synthesis via CO₂ Hydrogenation over Cu/ZnO Catalysts Catal. Sci. Technol. 2015, 5, 869– 881 DOI: 10.1039/C4CY00848K
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The role of copper particle size in low pressure methanol synthesis via CO2 hydrogenation over Cu/ZnO catalysts
Karelovic, Alejandro; Ruiz, Patricio
Catalysis Science & Technology (2015), 5 (2), 869-881CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
Cu/ZnO catalysts with different mean Cu particle sizes were prepd. by wet impregnation of copper nitrate onto a zinc oxide support. Their performance was studied in methanol synthesis reaction from CO2 and H2 at temps. between 160 and 225 °C and a pressure of 7 bar. Selective methanol formation is favored at lower temps. due to the suppression of CO prodn. Activation energies were 8-11 kcal mol-1 for methanol formation and 29-31 kcal mol-1 for CO formation and were similar for all the catalysts. For catalysts with copper cluster sizes between 8.5 and 37.3 nm, the methanol formation rates normalized by surface copper atoms were independent of copper particle size. On the contrary, CO formation rates are enhanced over catalysts with smaller copper clusters. Higher selectivity to methanol is favored over catalysts possessing larger copper nanoparticles. Catalysts with copper loading ≥8 wt.% showed a strong sintering of copper nanoparticles and also a significant growth of ZnO support crystallites. These catalysts presented higher intrinsic rates for methanol formation (4 × 10-3 s-1 at 180 °C) compared to catalysts with lower copper loading (0.9 × 10-3 s-1). As the kinetic parameters were similar for all Cu/ZnO catalysts, it is proposed that catalysts with large copper and ZnO particles form new active sites that led ultimately to a very high methanol synthesis activity and selectivity. It is suggested that the important sintering of Cu particles modifies the structure of copper promoting the hydrogenation rate in methanol synthesis.
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Wang, J. L.; Ando, R. A.; Camargo, P. H. C. Investigating the Plasmon-Mediated Catalytic Activity of AgAu Nanoparticles as a Function of Composition: Are Two Metals Better than One? ACS Catal. 2014, 4, 3815– 3819 DOI: 10.1021/cs501189m
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Investigating the Plasmon-Mediated Catalytic Activity of AgAu Nanoparticles as a Function of Composition: Are Two Metals Better than One?
Wang, J. L.; Ando, Romulo A.; Camargo, Pedro H. C.
ACS Catalysis (2014), 4 (11), 3815-3819CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
The surface plasmon resonance (SPR) excitation by visible light in plasmonic nanostructures can be put to work to mediate catalytic processes. However, the role of compn. in bimetallic nanoparticles over the SPR-mediated catalytic activity remains unclear. The authors studied herein the SPR-mediated catalytic activity of AgAu nanoparticles as a function of compn. toward the oxidn. of p-aminothiophenol to p,p'-dimercaptoazobenzene. A volcano-type relation between compn. and product conversion was obsd., with a max. activity obsd. for Ag0.19Au0.81 nanoparticles. The variations in catalytic activity could be explained by the balance between the matching of the excitation wavelength with SPR position and the plasmonic damping due to interband transitions >500 nm. Probably the precise control over compn. allows the fine-tuning of catalytic activity in SPR-mediated catalytic processes.
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He, R.; Wang, Y.; Wang, X.; Wang, Z.; Liu, G.; Zhou, W.; Wen, L.; Li, Q.; Wang, X.; Chen, X.; Zeng, J.; Hou, J. G. Facile Synthesis of Pentacle Gold-Copper Alloy Nanocrystals and Their Plasmonic and Catalytic Properties Nat. Commun. 2014, 5, 4327 DOI: 10.1038/ncomms5327
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Facile synthesis of pentacle gold-copper alloy nanocrystals and their plasmonic and catalytic properties
He, Rong; Wang, You-Cheng; Wang, Xiaoyong; Wang, Zhantong; Liu, Gang; Zhou, Wei; Wen, Longping; Li, Qunxiang; Wang, Xiaoping; Chen, Xiaoyuan; Zeng, Jie; Hou, J. G.
Nature Communications (2014), 5 (), 4327CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
The combination of gold and copper is a good way to pull down the cost of gold and ameliorate the instability of copper. Through shape control, the synergy of these two metals can be better exploited. Here, we report an aq. phase route to the synthesis of pentacle gold-copper alloy nanocrystals with fivefold twinning, the size of which can be tuned in the range from 45 to 200 nm. The growth is found to start from a decahedral core, followed by protrusion of branches along twinning planes. Pentacle products display strong localized surface plasmon resonance peaks in the near-IR region. Under irradn. by an 808-nm laser, 70-nm pentacle nanocrystals exhibit a notable photothermal effect to kill 4T1 murine breast tumors established on BALB/c mice. In addn., 70-nm pentacle nanocrystals show better catalytic activity than conventional citrate-coated 5-nm Au nanoparticles towards the redn. of p-nitrophenol to p-aminophenol by sodium borohydride.
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Santos Costa, J. C.; Corio, P.; Marcia Rossi, L. Catalytic Oxidation of Cinnamyl Alcohol Using Au – Ag Nanotubes Investigated by Surface-Enhanced Raman Spectroscopy Nanoscale 2015, 7, 8536– 8543 DOI: 10.1039/C5NR01064K
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Kiyonaga, T.; Jin, Q.; Kobayashi, H.; Tada, H. Size-Dependence of Catalytic Activity of Gold Nanoparticles Loaded on Titanium (IV) Dioxide for Hydrogen Peroxide Decomposition ChemPhysChem 2009, 10, 2935– 2938 DOI: 10.1002/cphc.200900596
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Size-Dependence of Catalytic Activity of Gold Nanoparticles Loaded on Titanium (IV) Dioxide for Hydrogen Peroxide Decomposition
Kiyonaga, Tomokazu; Jin, Qiliang; Kobayashi, Hisayoshi; Tada, Hiroaki
ChemPhysChem (2009), 10 (17), 2935-2938CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
Size-dependence of catalytic activity of gold nanoparticles loaded on titanium (IV) dioxide for hydrogen peroxide decompn. is discussed.
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Laoufi, I.; Saint-Lager, M. C.; Lazzari, R.; Jupille, J.; Robach, O.; Garaudée, S.; Cabailh, G.; Dolle, P.; Cruguel, H.; Bailly, A. Size and Catalytic Activity of Supported Gold Nanoparticles: An in Operando Study during CO Oxidation J. Phys. Chem. C 2011, 115, 4673– 4679 DOI: 10.1021/jp1110554
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Size and Catalytic Activity of Supported Gold Nanoparticles: An in Operando Study during CO Oxidation
Laoufi, I.; Saint-Lager, M.-C.; Lazzari, R.; Jupille, J.; Robach, O.; Garaudee, S.; Cabailh, G.; Dolle, P.; Cruguel, H.; Bailly, A.
Journal of Physical Chemistry C (2011), 115 (11), 4673-4679CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
The origin of the catalytic activity of gold nanoparticles remains debated despite extensive studies. This in operando work investigates the relationship between catalytic activity and size/shape of gold nanoparticles supported on TiO2(110) during CO oxidn. The nanoparticles were synthesized by vapor deposition in ultrahigh vacuum. Their geometry was monitored in the presence of O2, Ar, or a mixt. of O2 + CO and of Ar + CO by grazing incidence small-angle X-ray scattering simultaneously with the catalytic activity. The occurrence of CO oxidn. induces a sintering directly correlated to the reaction rate. The catalytic activity is optimum for a nanoparticle's diam. of 2.1 ± 0.3 nm and a height of about six at. layers. Below this size, the activity drop corresponds to a height decrease. Rescaling of activities obtained in different exptl. conditions shows consistency of these results with published data using both "model" and "real" catalysts.
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Bell, S. E. J.; McCourt, M. R. SERS Enhancement by Aggregated Au Colloids: Effect of Particle Size Phys. Chem. Chem. Phys. 2009, 11, 7455– 7462 DOI: 10.1039/b906049a
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SERS enhancement by aggregated Au colloids: effect of particle size
Bell, Steven E. J.; McCourt, Maighread R.
Physical Chemistry Chemical Physics (2009), 11 (34), 7455-7462CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
Aggregated Au colloids were widely used as SERS enhancing media for many years but to date there was no systematic study of the effect of the particle size on the enhancements given by simple aggregated Au colloid solns. Previous systematic studies on isolated particles in soln. or multiple particles deposited onto surfaces reported widely different optimum particle sizes for the same excitation wavelength and also disagreed on the extent to which surface plasmon absorption spectra were a good predictor of enhancement factors. The spectroscopic properties of a range of samples of monodisperse Au colloids with diams. ranging from 21 to 146 nm were studied in soln. The UV/visible absorption spectra of the colloids show complex changes as a function of aggregating salt (MgSO4) concn. which diminish when the colloid is fully aggregated. Under these conditions, the relative SERS enhancements provided by the variously sized colloids vary very significantly across the size range. The largest signals in the raw data are obsd. for 46 nm colloids but correction for the total surface area available to generate enhancement shows that particles with 74 nm diam. give the largest enhancement per unit surface area. The obsd. enhancements do not correlate with absorbance at the excitation wavelength but the large differences between differently sized colloids demonstrate that even in the randomly aggregated particle assemblies studied here, inhomogeneous broadening does not mask the underlying changes due to differences in particle diam.
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Zhang, Q.; Blom, D. A.; Wang, H. Nanoporosity-Enhanced Catalysis on Subwavelength Au Nanoparticles: A Plasmon-Enhanced Spectroscopic Study Chem. Mater. 2014, 26, 5131– 5142 DOI: 10.1021/cm502508d
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Nanoporosity-Enhanced Catalysis on Subwavelength Au Nanoparticles: a Plasmon-Enhanced Spectroscopic Study
Zhang, Qingfeng; Blom, Douglas A.; Wang, Hui
Chemistry of Materials (2014), 26 (17), 5131-5142CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
The authors show that subwavelength Au nanoparticles with nanoscale surface porosity represent a unique bifunctional nanostructure that serves as both high-performance SERS substrates and efficient surface catalysts, allowing one to unravel the kinetics and pathways of surface-catalyzed reactions with unprecedented sensitivity and detail through time-resolved plasmon-enhanced spectroscopic measurements. The origin of the nanoporosity-enhanced catalytic activity can be interpreted as a consequence of high abundance of undercoordinated surface atoms at the steps and kinks on the highly curved surfaces of Au porous nanoparticles. By measuring SERS signals from the monolayer mols. preadsorbed on the surfaces of Au porous nanoparticles, the authors gained quant. insights into the intrinsic kinetics and mechanisms of Au-catalyzed hydrogenation of arom. nitro compds. with minimal complication introduced by the mol. diffusion, adsorption, and desorption.
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Zhang, Q.; Wang, H. Facet-Dependent Catalytic Activities of Au Nanoparticles Enclosed by High-Index Facets ACS Catal. 2014, 4, 4027– 4033 DOI: 10.1021/cs501445h
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Facet-Dependent Catalytic Activities of Au Nanoparticles Enclosed by High-Index Facets
Zhang, Qingfeng; Wang, Hui
ACS Catalysis (2014), 4 (11), 4027-4033CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
We employed surface-enhanced Raman scattering as a noninvasive in situ spectroscopic tool to quant. study the intrinsic facet-dependent catalytic activities of colloidal subwavelength Au nanoparticles enclosed by various types of well-defined high-index facets using the catalytic hydrogenation of 4-nitrothiophenol as a model reaction. Our results provide compelling exptl. evidence on the crucial roles of undercoordinated surface atoms in Au-based heterogeneous catalysis and shed light on the underlying relationship between the at.-level surface structures and the intrinsic catalytic activities of Au nanocatalysts.
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Cui, Q.; Yashchenok, A.; Zhang, L.; Li, L.; Masic, A.; Wienskol, G.; Möhwald, H.; Bargheer, M. Fabrication of Bifunctional Gold/gelatin Hybrid Nanocomposites and Their Application ACS Appl. Mater. Interfaces 2014, 6, 1999– 2002 DOI: 10.1021/am5000068
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Fabrication of Bifunctional Gold/Gelatin Hybrid Nanocomposites and Their Application
Cui, Qianling; Yashchenok, Alexey; Zhang, Lu; Li, Lidong; Masic, Admir; Wienskol, Gabriele; Mohwald, Helmuth; Bargheer, Matias
ACS Applied Materials & Interfaces (2014), 6 (3), 1999-2002CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
A facile method is presented to integrate large gold nanoflowers (∼80 nm) and small gold nanoparticles (2-4 nm) into a single entity, exhibiting both surface-enhanced Raman scattering (SERS) and catalytic activity. The as-prepd. gold nanoflowers were coated by a gelatin layer, in which the gold precursor was adsorbed and in situ reduced into small gold nanoparticles. The thickness of the gelatin shell is controlled to less than 10 nm, ensuring that the small gold nanoparticles are still in a SERS-active range of the inner Au core. Therefore, the reaction catalyzed by these nanocomposites can be monitored in situ using label-free SERS spectroscopy. In addn., these bifunctional nanocomposites are also attractive candidates for application in SERS monitoring of bioreactions because of their excellent biocompatibility.
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Xie, W.; Walkenfort, B.; Schlücker, S. Label-Free SERS Monitoring of Chemical Reactions Catalyzed by Small Gold Nanoparticles Using 3D Plasmonic Superstructures J. Am. Chem. Soc. 2013, 135, 1657– 1660 DOI: 10.1021/ja309074a
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Label-Free SERS Monitoring of Chemical Reactions Catalyzed by Small Gold Nanoparticles Using 3D Plasmonic Superstructures
Xie, Wei; Walkenfort, Bernd; Schluecker, Sebastian
Journal of the American Chemical Society (2013), 135 (5), 1657-1660CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Label-free in situ surface-enhanced Raman scattering (SERS) monitoring of reactions catalyzed by small gold nanoparticles using rationally designed plasmonic superstructures is presented. Catalytic and SERS activities are integrated into a single bifunctional 3D superstructure comprising small gold satellites self-assembled onto a large shell-isolated gold core, which eliminates photocatalytic side reactions.
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van Schrojenstein Lantman, E. M. Raman Nanospectroscopy of a Photo-Catalytic Reaction. Ph.D. Thesis, Utrecht University, Utrecht, The Netherlands, 2014.
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Sun, M.; Xu, H. A Novel Application of Plasmonics: Plasmon-Driven Surface-Catalyzed Reactions Small 2012, 8, 2777– 2786 DOI: 10.1002/smll.201200572
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A Novel Application of Plasmonics: Plasmon-Driven Surface-Catalyzed Reactions
Sun, Mengtao; Xu, Hongxing
Small (2012), 8 (18), 2777-2786CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
A review. The first exptl. and theor. evidence of the surface-catalyzed reaction of p,p'-dimercaptoazobenzene (DMAB) produced from para-aminothiophenol (PATP) by local surface plasmons was reported in 2010, and since that time a series of investigations have supported these findings using different exptl. and theor. methods. Recent work has also found that local plasmons can drive a surface-catalyzed reaction of DMAB converted from 4-nitrobenzenethiol (4NBT), assisted by local surface plasmons. There are at least three important discoveries in these investigations: (1) in the field of surface-enhanced Raman scattering (SERS) the widely accepted misinterpretation (since 1994) that the chem. mechanism resulting in three addnl. Raman peaks of PATP in Ag or Au solns. has been cor. with a new mechanism; (2) it is confirmed that SERS is not always a noninvasive technique, and under certain conditions cannot always obtain the vibrational fingerprint information of the original surface species; (3) a novel method to synthesize new mols., induced by local surface plasmons or plasmon waveguides on the nanoscale, has been found. This Review considers recent novel applications of plasmonics to chem. reactions, esp. to plasmon-driven surface-catalyzed reactions.
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Harvey, C. E.; Weckhuysen, B. M. Surface- and Tip-Enhanced Raman Spectroscopy as Operando Probes for Monitoring and Understanding Heterogeneous Catalysis Catal. Lett. 2015, 145, 40– 57 DOI: 10.1007/s10562-014-1420-4
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Surface- and Tip-Enhanced Raman Spectroscopy as Operando Probes for Monitoring and Understanding Heterogeneous Catalysis
Harvey, Clare E.; Weckhuysen, Bert M.
Catalysis Letters (2015), 145 (1), 40-57CODEN: CALEER; ISSN:1011-372X. (Springer)
Abstr.: Surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS) were until recently limited in their applicability to the majority of heterogeneous catalytic reactions. Recent developments begin to resolve the conflicting exptl. requirements for SERS and TERS on the one hand, and heterogeneous catalysis on the other hand. This article discusses the development and use of SERS and TERS to study heterogeneous catalytic reactions, and the exciting possibilities that may now be within reach thanks to the latest tech. developments. This will be illustrated with showcase examples from photo- and electrocatalysis. Graphical Abstr.: [Figure not available: see fulltext.].
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Chen, X.-J.; Cabello, G.; Wu, D.-Y.; Tian, Z.-Q. Surface-Enhanced Raman Spectroscopy toward Application in Plasmonic Photocatalysis on Metal Nanostructures J. Photochem. Photobiol., C 2014, 21, 54– 80 DOI: 10.1016/j.jphotochemrev.2014.10.003
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Surface-enhanced Raman spectroscopy toward application in plasmonic photocatalysis on metal nanostructures
Chen, Xue-Jiao; Cabello, Gema; Wu, De-Yin; Tian, Zhong-Qun
Journal of Photochemistry and Photobiology, C: Photochemistry Reviews (2014), 21 (), 54-80CODEN: JPPCAF; ISSN:1389-5567. (Elsevier B.V.)
Among photothermal, photovoltaic and photochem. techniques, photochem. is superior in energy storage and transportation by converting photons into chem. fuels. Recently plasmonic photocatalysis, based on localized surface plasmon resonance (LSPR) generated from noble metal nanostructures, has attracted much attention. It promotes photochem. reaction efficiency by optimizing the solar spectrum absorption and the surface reaction kinetics. The deeper understanding is in urgent need for the development of novel plasmonic photocatalysts. Surface-enhanced Raman spectroscopy (SERS), which is also originated from the LSPR effect, provides an excellent opportunity to probe and monitor plasmonic photoreactions in situ and in real-time, with a very high surface sensitivity and energy resoln. Here, fundamentals of plasmonic photocatalysis and SERS are first presented based on their connections to the LSPR effect. Following by a validity anal., latest studies of SERS applied for the plasmon mediated photochem. reaction are reviewed, focusing on the reaction kinetics and mechanism exploration. Finally, limitations of the present study, as well as the future research directions, are briefly analyzed and discussed.
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Pashaee, F.; Hou, R.; Gobbo, P.; Workentin, M. S.; Lagugné-Labarthet, F. Tip-Enhanced Raman Spectroscopy of Self-Assembled Thiolated Monolayers on Flat Gold Nanoplates Using Gaussian-Transverse and Radially Polarized Excitations J. Phys. Chem. C 2013, 117, 15639– 15646 DOI: 10.1021/jp403157v
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Tip-Enhanced Raman Spectroscopy of Self-Assembled Thiolated Monolayers on Flat Gold Nanoplates Using Gaussian-Transverse and Radially Polarized Excitations
Pashaee, Farshid; Hou, Renjie; Gobbo, Pierangelo; Workentin, Mark S.; Lagugne-Labarthet, Francois
Journal of Physical Chemistry C (2013), 117 (30), 15639-15646CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
Tip-enhanced Raman spectroscopy (TERS) is a highly sensitive spectroscopic technique that combines the spatial resoln. of scanning near-field techniques with the chem. specificity of vibrational spectroscopy. TERS is based on the excitation of the localized surface plasmon resonance at the apex of an AFM metalized tip, producing a confined and enhanced electromagnetic field. Due to the inherent local nature of TERS and its confinement in the optical near-field of the object, TERS measurements can also be used to probe monolayers adsorbed onto surfaces providing better surface specificity in addn. to higher spatial resoln. The authors implement here gap-mode TERS using Au nanoplates functionalized with thiolated ref. mols. such as alkoxy substituted azobenzene thiol and 4-nitrothiophenol. The monolayer is probed with a Ag coated AFM tip to obtain the largest electromagnetic field enhancement from the surface plasmon localized between the Ag tip and the functionalized Au surface. The TERS spectra was measured of the self-assembled monolayer on Au using 532 nm excitation that is linearly (Gaussian-transverse TEM00) and radially polarized. The nature of the collected TERS spectra for the thiolated mols. (azobenzene thiol and nitrothiophenol) that appear to be dependent on the polarization of the excitation light at the tip/substrate interface is reported.
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Tabatabaei, M.; Sangar, A.; Kazemi-zanjani, N.; Torchio, P.; Merlen, A.; Lagugné-Labarthet, F. Optical Properties of Silver and Gold Tetrahedral Nanopyramid Arrays Prepared by Nanosphere Lithography J. Phys. Chem. C 2013, 117, 14778– 14786 DOI: 10.1021/jp405125c
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Optical Properties of Silver and Gold Tetrahedral Nanopyramid Arrays Prepared by Nanosphere Lithography
Tabatabaei, Mohammadali; Sangar, Alexandre; Kazemi-Zanjani, Nastaran; Torchio, Philippe; Merlen, Alexandre; Lagugne-Labarthet, Francois
Journal of Physical Chemistry C (2013), 117 (28), 14778-14786CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
Tetrahedral nanopyramids made of Ag and Au over ITO/glass surfaces are fabricated. The protocol is based on nanosphere lithog. (NSL) with the deposition of thicker metal layers. After removing the microspheres used in the NSL process, an array of metallic tetrahedral nanostructures of ∼350-400 nm height is formed. The reported procedure avoids the use of any stabilizing surfactant mols. that are generally necessary to segregate the individual particles onto surfaces. The authors focus here on the optical and the phys. properties of these plasmonic surfaces using near-field spectroscopy in conjunction with finite difference time domain (FDTD) modeling of the elec. field. Remarkably, FDTD shows that the localized surface plasmon resonance is confined in the plane formed by the edges of 2 facing pyramids that is parallel to the polarization of the impinging excitation laser. The variable gap between the edges of 2 adjacent pyramids shows a broader localized surface plasmon and a larger sp. surface as opposed to the usual nanotriangle array. Localized enhancement of the elec. field is exptl. studied by coating the plasmonic surface with a thin film of photosensitive azopolymer onto the surface of the nanopyramids. Upon irradn., the deformation of the surface topog. is visualized by at. force microscopy and suggests the potentiality of these 3D nanopyramids for near-field enhancement. This last feature is clearly confirmed by surface-enhanced Raman scattering measurement with 4-nitrothiophenol mols. deposited on the pyramid platforms. The potentiality of such 3D nanostructures in plasmonics and surface spectroscopy is thus clearly demonstrated.
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Liu, W.-L.; Lin, F.-C.; Yang, Y.-C.; Huang, C.-H.; Gwo, S.; Huang, M. H.; Huang, J.-S. The Influence of Shell Thickness of Au@TiO₂ Core-Shell Nanoparticles on the Plasmonic Enhancement Effect in Dye-Sensitized Solar Cells Nanoscale 2013, 5, 7953– 7962 DOI: 10.1039/c3nr02800c
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The influence of shell thickness of Au@TiO2 core-shell nanoparticles on the plasmonic enhancement effect in dye-sensitized solar cells
Liu, Wei-Liang; Lin, Fan-Cheng; Yang, Yu-Chen; Huang, Chen-Hsien; Gwo, Shangjr; Huang, Michael H.; Huang, Jer-Shing
Nanoscale (2013), 5 (17), 7953-7962CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
Plasmonic core-shell nanoparticles (PCSNPs) can function as nanoantennas and improve the efficiency of dye-sensitized solar cells (DSSCs). To achieve max. enhancement, the morphol. of PCSNPs needs to be optimized. Here we precisely control the morphol. of AuiO2 PCSNPs and systematically study its influence on the plasmonic enhancement effect. The enhancement mechanism was found to vary with the thickness of the TiO2 shell. PCSNPs with a thinner shell mainly enhance the current, whereas particles with a thicker shell improve the voltage. While pronounced plasmonic enhancement was found in the near IR regime, wavelength-independent enhancement in the visible range was obsd. and attributed to the plasmonic heating effect. Emission lifetime measurement confirms that N719 mols. neighboring nanoparticles with TiO2 shells exhibit a longer lifetime than those in contact with metal cores. Overall, PCSNPs with a 5 nm shell give the highest efficiency enhancement of 23%. Our work provides a new synthesis route for well-controlled AuiO2 core-shell nanoparticles and gains insight into the plasmonic enhancement in DSSCs.
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Zhang, Z.; Deckert-Gaudig, T.; Singh, P.; Deckert, V. Single Molecule Level Plasmonic Catalysis – a Dilution Study of p-Nitrothiophenol on Gold Dimers Chem. Commun. 2015, 51, 3069– 3072 DOI: 10.1039/C4CC09008J
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Single molecule level plasmonic catalysis - a dilution study of p-nitrothiophenol on gold dimers
Zhang, Zhenglong; Deckert-Gaudig, Tanja; Singh, Pushkar; Deckert, Volker
Chemical Communications (Cambridge, United Kingdom) (2015), 51 (15), 3069-3072CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
Surface plasmons on isolated gold dimers can initiate intermol. reactions of adsorbed p-nitrothiophenol. At the single mol. level when dimerization is not possible an intramol. reaction can be obsd. Exptl. evidence indicates that plasmon-induced hot electrons provide the required activation energy.
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Wang, P.; Huang, B.; Dai, Y.; Whangbo, M.-H. Plasmonic Photocatalysts: Harvesting Visible Light with Noble Metal Nanoparticles Phys. Chem. Chem. Phys. 2012, 14, 9813– 9825 DOI: 10.1039/c2cp40823f
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Plasmonic photocatalysts: harvesting visible light with noble metal nanoparticles
Wang, Peng; Huang, Baibiao; Dai, Ying; Whangbo, Myung-Hwan
Physical Chemistry Chemical Physics (2012), 14 (28), 9813-9825CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
A review. The efforts to produce photocatalysts operating efficiently under visible light have led to a no. of plasmonic photocatalysts, in which noble metal nanoparticles are deposited on the surface of polar semiconductor or dielecs. particles. In the metal-semiconductor composite photocatalysts, the noble metal nanoparticles act as a major component for harvesting visible light due to their surface plasmon resonance while the metal-semiconductor interface efficiently separates the photogenerated electrons and holes. In this article, we survey various plasmonic photocatalysts that have been prepd. and characterized in recent years.
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Rycenga, M.; Wang, Z.; Gordon, E.; Cobley, C. M.; Schwartz, A. G.; Lo, C. S.; Xia, Y. Probing the Photothermal Effect of Gold-Based Nanocages with Surface Enhanced Raman Scattering (SERS) Angew. Chem., Int. Ed. 2009, 48, 9924– 9927 DOI: 10.1002/anie.200904382
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Kang, T.; Hong, S.; Choi, Y.; Lee, L. P. The Effect of Thermal Gradients in SERS Spectroscopy Small 2010, 6, 2649– 2652 DOI: 10.1002/smll.201000996
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The Effect of Thermal Gradients in SERS Spectroscopy
Kang, Taewook; Hong, Soongweon; Choi, Yeonho; Lee, Luke P.
Small (2010), 6 (23), 2649-2652CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
This study demonstrated the importance of temp. gradients due to photothermal effects on nanoplasmonic antennae in surface enhanced Raman scattering (SERS) spectroscopic measurements. Using 5-carboxytetramethylrhodamine (TAMRA)-labeled DNA, crit. photothermal effect in SERS spectroscopic measurements was obsd. Numerical anal. and exptl. results revealed that the local concn. of the target mols. near a SERS probe was not the same as the bulk concn., and this made a significant difference in sensitivity of the probes. Since SERS results showed that DNA could be not only depleted, but also enriched in adjacent areas, both these regions may be controlled by changing the shape or array of probes, the power of the excitation source, the chamber height, and the substrate materials. Crit. understanding of photothermal effects and temp. gradients can be applied to maximize the amplification of SERS signals and the effective design of sensitive SERS probes by inducing target mols. to focus on enrichment sites for future label-free biochem., chem., and environmental monitoring.
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Zhao, L.-B.; Huang, Y.-F.; Liu, X.-M.; Anema, J. R.; Wu, D.-Y.; Ren, B.; Tian, Z.-Q. A DFT Study on Photoinduced Surface Catalytic Coupling Reactions on Nanostructured Silver: Selective Formation of Azobenzene Derivatives from Para-Substituted Nitrobenzene and Aniline Phys. Chem. Chem. Phys. 2012, 14, 12919– 12929 DOI: 10.1039/c2cp41502j
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A DFT study on photoinduced surface catalytic coupling reactions on nanostructured silver: selective formation of azobenzene derivatives from para-substituted nitrobenzene and aniline
Zhao, Liu-Bin; Huang, Yi-Fan; Liu, Xiu-Min; Anema, Jason R.; Wu, De-Yin; Ren, Bin; Tian, Zhong-Qun
Physical Chemistry Chemical Physics (2012), 14 (37), 12919-12929CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
We propose that arom. nitro and amine compds. undergo photochem. reductive and oxidative coupling, resp., to specifically produce azobenzene derivs. which exhibit characteristic Raman signals related to the azo group. A photoinduced charge transfer model is presented to explain the transformations obsd. in para-substituted ArNO2 and ArNH2 on nanostructured silver due to the surface plasmon resonance effect. Theor. calcns. show that the initial reaction takes place through excitation of an electron from the filled level of silver to the LUMO of an adsorbed ArNO2 mol., and from the HOMO of an adsorbed ArNH2 mol. to the unoccupied level of silver, during irradn. with visible light. The para-substituted ArNO2-· and ArNH2+· surface species react further to produce the azobenzene derivs. Our results may provide a new strategy for the syntheses of arom. azo dyes from arom. nitro and amine compds. based on the use of nanostructured silver as a catalyst.
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Pelaez, M.; Nolan, N. T.; Pillai, S. C.; Seery, M. K.; Falaras, P.; Kontos, A. G.; Dunlop, P. S. M.; Hamilton, J. W. J.; Byrne, J. A.; Shea, K. O. A Review on the Visible Light Active Titanium Dioxide Photocatalysts for Environmental Applications Appl. Catal., B 2012, 125, 331– 349 DOI: 10.1016/j.apcatb.2012.05.036
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A review on the visible light active titanium dioxide photocatalysts for environmental applications
Pelaez, Miguel; Nolan, Nicholas T.; Pillai, Suresh C.; Seery, Michael K.; Falaras, Polycarpos; Kontos, Athanassios G.; Dunlop, Patrick S. M.; Hamilton, Jeremy W. J.; Byrne, J. Anthony; O'Shea, Kevin; Entezari, Mohammad H.; Dionysiou, Dionysios D.
Applied Catalysis, B: Environmental (2012), 125 (), 331-349CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
A review. Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO2) semiconductor materials to split water into hydrogen and oxygen in a photo-electrochem. cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applications. One of the most significant scientific and com. advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 structure, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochem. and photoelectrochem. methods. Various applications of VLA TiO2, in terms of environmental remediation and in particular water treatment, disinfection and air purifn., are illustrated. Comprehensive studies on the photocatalytic degrdn. of contaminants of emerging concern, including endocrine disrupting compds., pharmaceuticals, pesticides, cyanotoxins and volatile org. compds., with VLA TiO2 are discussed and compared to conventional UV-activated TiO2 nanomaterials. Recent advances in bacterial disinfection using VLA TiO2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted.
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Huang, W.; Jing, Q.; Du, Y.; Zhang, B.; Meng, X.; Sun, M.; Schanze, K. S.; Gao, H.; Xu, P. An in Situ SERS Study of Substrate-Dependent Surface Plasmon Induced Aromatic Nitration J. Mater. Chem. C 2015, 3, 5285– 5291 DOI: 10.1039/C5TC00835B
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An in situ SERS study of substrate-dependent surface plasmon induced aromatic nitration
Huang, Wei; Jing, Qiang; Du, Yunchen; Zhang, Bin; Meng, Xiangli; Sun, Mengtao; Schanze, Kirk S.; Gao, Hong; Xu, Ping
Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2015), 3 (20), 5285-5291CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
Surface plasmon (SP)-induced nitration of arom. rings has been demonstrated by an in situ surface enhanced Raman spectroscopy (SERS) technique. The size feature of the as-prepd. Au, Ag and Ag@PDA@Au hierarchical structures allows monitoring the entire reaction process on a single hierarchical structure. With benzenethiol (BT) and HNO3 as reactants, SP induced arom. nitration can be successfully realized without the assistance of a conventional acid catalyst, H2SO4. Exptl. and theor. studies confirm that the nitration reaction leads to para-nitrothiophenol (p-NTP). While control expts. show that SP here functions as a local heating source and the presence of metal is also necessary for this nitration reaction. This SP induced arom. nitration reaction also displays SERS substrate-dependent reaction kinetics, which proceeds more rapidly on the Au surface. Higher laser power can generate a stronger photothermal effect, and thus an accelerated reaction rate for this reaction.
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Knight, M. W.; King, N. S.; Liu, L.; Everitt, H. O.; Nordlander, P.; Halas, N. J. Aluminium for Plasmonics ACS Nano 2014, 8, 834– 840 DOI: 10.1021/nn405495q
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Aluminum for Plasmonics
Knight, Mark W.; King, Nicholas S.; Liu, Lifei; Everitt, Henry O.; Nordlander, Peter; Halas, Naomi J.
ACS Nano (2014), 8 (1), 834-840CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
Unlike Ag and Au, Al has material properties that enable strong plasmon resonances spanning much of the visible region of the spectrum and into the UV. This extended response, combined with its natural abundance, low cost, and amenability to manufg. processes, makes Al a highly promising material for com. applications. Fabricating Al-based nanostructures whose optical properties correspond with theor. predictions, however, can be a challenge. The Al plasmon resonance is remarkably sensitive to the presence of oxide within the metal. For Al nanodisks, the energy of the plasmon resonance is detd. by, and serves as an optical reporter of, the percentage of oxide present within the Al. This understanding paves the way toward the use of Al as a low-cost plasmonic material with properties and potential applications similar to those of the coinage metals.
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McMahon, J. M.; Gray, S. K.; Schatz, G. C. Ultraviolet Plasmonics: The Poor Metals Al, Ga, In, Sn, Tl, Pb, and Bi Phys. Chem. Chem. Phys. 2013, 15, 5415– 5423 DOI: 10.1039/C3CP43856B
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Plasmonics in the ultraviolet with the poor metals Al, Ga, In, Sn, Tl, Pb, and Bi
McMahon, Jeffrey M.; Schatz, George C.; Gray, Stephen K.
Physical Chemistry Chemical Physics (2013), 15 (15), 5415-5423CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
How the poor metals Al, Ga, In, Sn, Tl, Pb, and Bi can be used for plasmonics in the near to far UV range, similar to the noble metals Ag and Au in the visible (visible) range are discussed. The authors 1st discuss the empirical dielec. functions of the poor metals, contrasting them with Ag and Au, and also fitting them to a Drude and multiple Lorentz oscillator form. Using Mie theory, the authors then compare the optical responses of spherical poor metal nanoparticles to noble metal ones. Finally, nanoparticle dimers are studied using a vectorial finite element method. The poor metals exhibit large elec. field enhancements in the UV, comparable to Au in the visible, which makes them particularly attractive for sensing applications, such as surface enhanced Raman spectroscopy.
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Yin, P.-G.; Jiang, L.; You, T.-T.; Zhou, W.; Li, L.; Guo, L.; Yang, S. Surface-Enhanced Raman Spectroscopy with Self-Assembled Cobalt Nanoparticle Chains: Comparison of Theory and Experiment Phys. Chem. Chem. Phys. 2010, 12, 10781– 10785 DOI: 10.1039/c002662j
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85
Tian, Z.-Q.; Ren, B.; Li, J.-F.; Yang, Z.-L. Expanding Generality of Surface-Enhanced Raman Spectroscopy with Borrowing SERS Activity Strategy Chem. Commun. 2007, 34, 3514– 3534 DOI: 10.1039/b616986d
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There is no corresponding record for this reference.
86
Heck, K. N.; Janesko, B. G.; Scuseria, G. E.; Halas, N. J.; Wong, M. S. Observing Metal-Catalyzed Chemical Reactions in Situ Using Surface-Enhanced Raman Spectroscopy on Pd-Au Nanoshells J. Am. Chem. Soc. 2008, 130, 16592– 16600 DOI: 10.1021/ja803556k
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Observing Metal-Catalyzed Chemical Reactions in Situ Using Surface-Enhanced Raman Spectroscopy on Pd-Au Nanoshells
Heck, Kimberly N.; Janesko, Benjamin G.; Scuseria, Gustavo E.; Halas, Naomi J.; Wong, Michael S.
Journal of the American Chemical Society (2008), 130 (49), 16592-16600CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Insight into the nature of transient reaction intermediates and mechanistic pathways involved in heterogeneously catalyzed chem. reactions is obtainable from a no. of surface spectroscopic techniques. Carrying out these investigations under actual reaction conditions is preferred but remains challenging, esp. for catalytic reactions that occur in water. Here, we report the direct spectroscopic study of the catalytic hydrodechlorination of 1,1-dichloroethene in H2O using surface-enhanced Raman spectroscopy (SERS). With Pd islands grown on Au nanoshell films, this reaction can be followed in situ using SERS, exploiting the high enhancements and large active area of Au nanoshell SERS substrates, the transparency of Raman spectroscopy to aq. solvents, and the catalytic activity enhancement of Pd by the underlying Au metal. The formation and subsequent transformation of several adsorbate species was obsd. These results provide the first direct evidence of the room-temp. catalytic hydrodechlorination of a chlorinated solvent, a potentially important pathway for groundwater cleanup, as a sequence of dechlorination and hydrogenation steps. More broadly, the results highlight the exciting prospects of studying catalytic processes in water in situ, like those involved in biomass conversion and proton-exchange membrane fuel cells.
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Mahmoud, M. A.; Garlyyev, B.; El-sayed, M. A. Controlling the Catalytic Efficiency on the Surface of Hollow Gold Nanoparticles by Introducing an Inner Thin Layer of Platinum or Palladium J. Phys. Chem. Lett. 2014, 5, 4088– 4094 DOI: 10.1021/jz502071v
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Controlling the Catalytic Efficiency on the Surface of Hollow Gold Nanoparticles by Introducing an Inner Thin Layer of Platinum or Palladium
Mahmoud, Mahmoud A.; Garlyyev, Batyr; El-Sayed, Mostafa A.
Journal of Physical Chemistry Letters (2014), 5 (23), 4088-4094CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
The efficiency of heterogeneous catalysis of electron-transfer reactions on the surface of gold nanoshells was changed by adding an inner platinum or palladium nanoshell in the double-shell nanocatalysts. The redn. of 4-nitrothiophenol (4NTP) by borohydride was studied as a model reaction. To confirm the heterogeneous catalytic mechanism, the nanocatalysts were assembled into a monolayer on the surface of a quartz substrate using the Langmuir-Blodgett technique, and the 4NTP was allowed to bind to the surface of gold through a strong thiol bond. The stages of the redn. reaction of 4NTP on the surface of gold were successfully followed by time-resolved surface-enhanced Raman spectroscopy. Palladium was found to increase the catalytic efficiency of the gold surface due to the presence of a new Fermi level of the palladium-gold alloy, while platinum decreased its catalytic efficiency due to the electron-withdrawing effect of platinum atoms, which resulted from the difference in their electrochem. redn. potentials.
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El-Aziz, A. M.; Kibler, L. A.; Kolb, D. M. The Potentials of Zero Charge of Pd(111) and Thin Pd Overlayers on Au(111) Electrochem. Commun. 2002, 4, 535– 539 DOI: 10.1016/S1388-2481(02)00362-4
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The potentials of zero charge of Pd(1 1 1) and thin Pd overlayers on Au(1 1 1)
El-Aziz, A. M.; Kibler, L. A.; Kolb, D. M.
Electrochemistry Communications (2002), 4 (7), 535-539CODEN: ECCMF9; ISSN:1388-2481. (Elsevier Science B.V.)
The potential of zero charge (pzc) of Pd(1 1 1) was detd. in dil. NaF solns. by measuring the Gouy-Chapman min. of the double-layer capacity. For a massive Pd(1 1 1) single crystal electrode a pzc of -0.12 V vs. SCE was found. The corresponding values for thin Pd(1 1 1) overlayers on Au(1 1 1) also were detd. While the pzc of the 1st, pseudomorphic Pd layer on Au(1 1 1) is -0.09 V vs. SCE, the pzc of a five monolayers thick Pd film on Au(1 1 1) is practically identical to the pzc of the massive Pd(1 1 1) electrode. By comparing pzc's and work functions for Au(1 1 1) and Pd(1 1 1), the dipole contribution to the potential drop across the Pd(1 1 1)/H2O interface is estd.
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Attard, G. A.; Bennett, J. A.; Mikheenko, I.; Jenkins, P.; Guan, S.; Macaskie, L. E.; Wood, J.; Wain, A. J. Semi-Hydrogenation of Alkynes at Single Crystal, Nanoparticle and Biogenic Nanoparticle Surfaces: The Role of Defects in Lindlar-Type Catalysts and the Origin of Their Selectivity Faraday Discuss. 2013, 162, 57– 75 DOI: 10.1039/c3fd00007a
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Semi-hydrogenation of alkynes at single crystal, nanoparticle and biogenic nanoparticle surfaces: the role of defects in Lindlar-type catalysts and the origin of their selectivity
Attard, G. A.; Bennett, J. A.; Mikheenko, I.; Jenkins, P.; Guan, S.; Macaskie, L. E.; Wood, J.; Wain, A. J.
Faraday Discussions (2013), 162 (Fabrication, Structure and Reactivity of Anchored Nanoparticles), 57-75CODEN: FDISE6; ISSN:1359-6640. (Royal Society of Chemistry)
For the first time, the method of shell-isolated nanoparticle Raman spectroscopy (SHINERS) is used in combination with cyclic voltammetry (CV) and reactivity studies to study the adsorption behavior of three alkynes undergoing hydrogenation on nanoparticle, single crystal and bacteria/graphite-supported platinum surfaces. A strong assocn. of alkynes with defect sites to produce a long-lived di-sigma/pi-alkene surface complex allows for deep hydrogenation of this intermediate to the alkane product. But when platinum surface defect sites are blocked by either bismuth or polyvinylpyrrolidone (PVP) (and thus leaving behind only Pt{111} terrace adsorption sites), large increases in selectivity to the semi-hydrogenation product are obsd. for all three alkynes. This finding is consistent with SHINERS collected from both well-ordered and roughened Pt{111} electrodes which revealed that the di-sigma/pi-bonded surface intermediate is hardly formed at all on Pt{111} unless defect sites are introduced via electrochem. roughening. As a general method of producing selective catalysts, the elimination of toxic heavy metals from Lindlar-type catalyst, used commonly in org. chem., and their replacement by more benign, org. species adsorbed at defect sites is discussed.
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Porter, M. D.; Lipert, R. J.; Siperko, L. M.; Wang, G.; Narayanan, R. SERS as a Bioassay Platform: Fundamentals, Design, and Applications Chem. Soc. Rev. 2008, 37, 1001– 1011 DOI: 10.1039/b708461g
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90
SERS as a bioassay platform: fundamentals, design, and applications
Porter, Marc D.; Lipert, Robert J.; Siperko, Lorraine M.; Wang, Gufeng; Narayanan, Radha
Chemical Society Reviews (2008), 37 (5), 1001-1011CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
A review. Bioanal. science is experiencing a period of unprecedented growth. Drivers behind this growth include the need to detect markers central to human and veterinary diagnostics at ever-lower levels and greater speeds. A set of parallel arguments applies to pathogens with respect to bioterrorism prevention and food and water safety. This tutorial review outlines the authors' recent explorations on the use of surface enhanced Raman scattering (SERS) for detection of proteins, viruses, and microorganisms in heterogeneous immunoassays. It will detail the design and fabrication of the assay platform, including the capture substrate and nanoparticle-based labels. The latter, which is the cornerstone of the authors' strategy, relies on the construction of gold nanoparticles modified with both an intrinsically strong Raman scatterer and an antibody. This labeling motif, referred to as extrinsic Raman labels (ERLs), takes advantage of the well-established signal enhancement of scatterers when coated on nanometer-sized gold particles, whereas the antibody imparts antigenic specificity. The authors will also examine the role of plasmon coupling between the ERLs and capture substrate, and challenges related to particle stability, nonspecific adsorption, and assay speed.
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Li, J. F.; Huang, Y. F.; Ding, Y.; Yang, Z. L.; Li, S. B.; Zhou, X. S.; Fan, F. R.; Zhang, W.; Zhou, Z. Y.; Wu, D. Y.; Ren, B.; Wang, Z. L.; Tian, Z. Q. Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy Nature 2010, 464, 392– 395 DOI: 10.1038/nature08907
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91
Shell-isolated nanoparticle-enhanced Raman spectroscopy
Li, Jian Feng; Huang, Yi Fan; Ding, Yong; Yang, Zhi Lin; Li, Song Bo; Zhou, Xiao Shun; Fan, Feng Ru; Zhang, Wei; Zhou, Zhi You; Wu, De Yin; Ren, Bin; Wang, Zhong Lin; Tian, Zhong Qun
Nature (London, United Kingdom) (2010), 464 (7287), 392-395CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
Surface-enhanced Raman scattering (SERS) is a powerful spectroscopy technique that can provide non-destructive and ultra-sensitive characterization down to single mol. level, comparable to single-mol. fluorescence spectroscopy. However, generally substrates based on metals such as Ag, Au and Cu, either with roughened surfaces or in the form of nanoparticles, are required to realize a substantial SERS effect, and this has severely limited the breadth of practical applications of SERS. A no. of approaches have extended the technique to non-traditional substrates, most notably tip-enhanced Raman spectroscopy (TERS) where the probed substance (mol. or material surface) can be on a generic substrate and where a nanoscale gold tip above the substrate acts as the Raman signal amplifier. The drawback is that the total Raman scattering signal from the tip area is rather weak, thus limiting TERS studies to mols. with large Raman cross-sections. Here, we report an approach, which we name shell-isolated nanoparticle-enhanced Raman spectroscopy, in which the Raman signal amplification is provided by gold nanoparticles with an ultrathin silica or alumina shell. A monolayer of such nanoparticles is spread as 'smart dust' over the surface that is to be probed. The ultrathin coating keeps the nanoparticles from agglomerating, separates them from direct contact with the probed material and allows the nanoparticles to conform to different contours of substrates. High-quality Raman spectra were obtained on various mols. adsorbed at Pt and Au single-crystal surfaces and from Si surfaces with hydrogen monolayers. These measurements and our studies on yeast cells and citrus fruits with pesticide residues illustrate that our method significantly expands the flexibility of SERS for useful applications in the materials and life sciences, as well as for the inspection of food safety, drugs, explosives and environment pollutants.
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Li, X.; Liu, M.; Lee, J.; Ding, D.; Bottomley, L. A.; Park, S.; Liu, M. An Operando Surface Enhanced Raman Spectroscopy (SERS) Study of Carbon Deposition on SOFC Anodes Phys. Chem. Chem. Phys. 2015, 17, 21112– 21119 DOI: 10.1039/C4CP05176A
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An operando surface enhanced Raman spectroscopy (SERS) study of carbon deposition on SOFC anodes
Li, Xiaxi; Liu, Mingfei; Lee, Jung-pil; Ding, Dong; Bottomley, Lawrence A.; Park, Soojin; Liu, Meilin
Physical Chemistry Chemical Physics (2015), 17 (33), 21112-21119CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
Thermally robust and chem. inert Ag@SiO2 nanoprobes are employed to provide the surface enhanced Raman scattering (SERS) effect for an in situ/operando study of the early stage of carbon deposition on nickel-based solid oxide fuel cell (SOFC) anodes. The enhanced sensitivity to carbon enables the detection of different stages of coking, offering insights into intrinsic coking tolerance of material surfaces. Application of a thin coating of gadolinium doped ceria (GDC) enhances the resistance to coking of nickel surfaces. The electrochem. active Ni-YSZ interface appears to be more active for hydrocarbon reforming, resulting in the accumulation of different hydrocarbon mols., which can be readily removed upon the application of an anodic current. Operando SERS is a powerful tool for the mechanistic study of coking in SOFC systems. It is also applicable to the study of other catalytic and electrochem. processes in a wide range of conditions.
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Li, X.; Lee, J.-P.; Blinn, K. S.; Chen, D.; Yoo, S.; Kang, B.; Bottomley, L. A.; El-Sayed, M. A.; Park, S.; Liu, M. High-Temperature Surface Enhanced Raman Spectroscopy for in Situ Study of Solid Oxide Fuel Cell Materials Energy Environ. Sci. 2014, 7, 306– 310 DOI: 10.1039/C3EE42462F
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High-temperature surface enhanced Raman spectroscopy for in situ study of solid oxide fuel cell materials
Li, Xiaxi; Lee, Jung-Pil; Blinn, Kevin S.; Chen, Dongchang; Yoo, Seungmin; Kang, Bin; Bottomley, Lawrence A.; El-Sayed, Mostafa A.; Park, Soojin; Liu, Meilin
Energy & Environmental Science (2014), 7 (1), 306-310CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)
In situ probing of surface species and incipient phases is vital to unraveling the mechanisms of chem. and energy transformation processes. Here we report Ag nanoparticles coated with a thin-film SiO2 shell that demonstrate excellent thermal robustness and chem. stability for surface enhanced Raman spectroscopy (SERS) study of solid oxide fuel cell materials under in situ conditions (at ∼400 °C).
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Whitney, A. V.; Elam, J. W.; Stair, P. C.; Van Duyne, R. P. Toward a Thermally Robust Operando Surface-Enhanced Raman Spectroscopy Substrate J. Phys. Chem. C 2007, 111, 16827– 16832 DOI: 10.1021/jp074462b
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94
Toward a Thermally Robust Operando Surface-Enhanced Raman Spectroscopy Substrate
Whitney, Alyson V.; Elam, Jeffrey W.; Stair, Peter C.; Van Duyne, Richard P.
Journal of Physical Chemistry C (2007), 111 (45), 16827-16832CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
The work presented here describes the first steps toward designing a thermally robust surface-enhanced Raman spectroscopy (SERS) substrate with the potential to conduct in situ monitoring of catalytic reactions. Nanosphere lithog. (NSL) fabricated SERS substrates were coated with thin (0.2-1.0 nm) films of at. layer deposited (ALD) Al2O3. The thermal stability of these substrates was examd. at various temps. (100-500° C) and over time (up to 6 h) in nitrogen. The results showed that ALD Al2O3 coated nanoparticles maintained their original geometry significantly better than the bare Ag nanoparticles. While expts. showed that thicker ALD Al2O3 coatings resulted in the most stable nanoparticle structure, ALD Al2O3 coatings as thin as 0.2 nm resulted in thermally robust nanostructures as well. Addnl., the ALD Al2O3 coated nanoparticles were heated under propane to mimic reaction conditions. These expts. showed that while the nanoparticle geometries were not as stable under reducing atm. conditions, they were much more stable than uncoated nanoparticles and therefore have the potential to be used for SERS monitoring of reactions conducted at elevated temps.
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Guan, S.; Donovan-sheppard, O.; Reece, C.; Willock, D. J.; Wain, A. J.; Attard, G. A. Structure Sensitivity in Catalytic Hydrogenation at Platinum Surfaces Measured by Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy (SHINERS) ACS Catal. 2016, 6, 1822 DOI: 10.1021/acscatal.5b02872
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95
Structure Sensitivity in Catalytic Hydrogenation at Platinum Surfaces Measured by Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy (SHINERS)
Guan, Shaoliang; Donovan-Sheppard, Oliver; Reece, Christian; Willock, David J.; Wain, Andrew J.; Attard, Gary A.
ACS Catalysis (2016), 6 (3), 1822-1832CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
The in situ combination of electrochem. and shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) was used for the 1st time to study the surface structure sensitivity of asym. catalytic hydrogenation at single-crystal Pt electrodes. The adsorption and hydrogenation behavior of aq. Et pyruvate (EP) at a range of modified and unmodified Pt{hkl} electrodes was measured both by cyclic voltammetry and by recording Raman spectra at H evolution potentials. Two primary surface intermediates were obsd., including the previously reported half-hydrogenation state (HHS), formed by addn. of a H atom to the keto carbonyl group, as well as a new species identified as intact chemisorbed EP bound in a μ2(C,O) configuration. The relative populations of these two species were sensitive to the Pt surface structure; whereas the μ2(C,O) EP adsorbate was dominant at pristine Pt{111} and Pt{100}, the HHS was only obsd. at these electrodes after the introduction of defects by electrochem. roughening. Intrinsically defective Pt{110} and kinked Pt{321} and Pt{721} surfaces exhibited behavior similar to that of electrochem. roughened basal surfaces, indicating the requirement for low coordination sites for observation of the HHS. Rationalization of the differing behaviors is given from d. functional theory (DFT) calcns., which indicate that the μ2(C,O) EP adsorbate is considerably more stable on basal {111} than on {221} stepped surfaces. A mechanism is proposed in which the μ2(C,O)-bound species is a precursor to the HHS but the rate of the 1st H atom addn. is slow, leading to a low steady-state population of the HHS at terrace sites. The implications of this in the context of enantioselective hydrogenation at chirally modified Pt are discussed.
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Rong, Z.; Xiao, R.; Wang, C.; Wang, D.; Wang, S. Plasmonic Ag Core–Satellite Nanostructures with a Tunable Silica- Spaced Nanogap for Surface-Enhanced Raman Scattering Langmuir 2015, 31, 8129– 8137 DOI: 10.1021/acs.langmuir.5b01713
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Xie, W.; Schlücker, S. Hot Electron-Induced Reduction of Small Molecules on Photorecycling Metal Surfaces Nat. Commun. 2015, 6, 7570 DOI: 10.1038/ncomms8570
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Hot electron-induced reduction of small molecules on photorecycling metal surfaces
Xie Wei; Schlucker Sebastian
Nature communications (2015), 6 (), 7570 ISSN:.
Noble metals are important photocatalysts due to their ability to convert light into chemical energy. Hot electrons, generated via the non-radiative decay of localized surface plasmons, can be transferred to reactants on the metal surface. Unfortunately, the number of hot electrons per molecule is limited due to charge-carrier recombination. In addition to the reduction half-reaction with hot electrons, also the corresponding oxidation counter-half-reaction must take place since otherwise the overall redox reaction cannot proceed. Here we report on the conceptual importance of promoting the oxidation counter-half-reaction in plasmon-mediated catalysis by photorecycling in order to overcome this general limitation. A six-electron photocatalytic reaction occurs even in the absence of conventional chemical reducing agents due to the photoinduced recycling of Ag atoms from hot holes in the oxidation half-reaction. This concept of multi-electron, counter-half-reaction-promoted photocatalysis provides exciting new opportunities for driving efficient light-to-energy conversion processes.
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Xie, W.; Herrmann, C.; Kömpe, K.; Haase, M.; Schlücker, S. Synthesis of Bifunctional Au/Pt/Au Core/shell Nanoraspberries for in Situ SERS Monitoring of Platinum-Catalyzed Reactions J. Am. Chem. Soc. 2011, 133, 19302– 19305 DOI: 10.1021/ja208298q
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Synthesis of Bifunctional Au/Pt/Au Core/Shell Nanoraspberries for in Situ SERS Monitoring of Platinum-Catalyzed Reactions
Xie, Wei; Herrmann, Christoph; Koempe, Karsten; Haase, Markus; Schluecker, Sebastian
Journal of the American Chemical Society (2011), 133 (48), 19302-19305CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The synthesis of bifunctional Au/Pt/Au nanoraspberries for use in quant. in situ monitoring of platinum-catalyzed reactions by surface-enhanced Raman scattering (SERS) is presented. Highly convolved SERS spectra of reaction mixts. can be decompd. into the contributions of distinct mol. species by multivariate data anal.
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Kha, N. M.; Chen, C.-H.; Su, W.-N.; Rick, J.; Hwang, B.-J. Improved Raman and Photoluminescence Sensitivity Achieved Using Bifunctional Ag@SiO₂ Nanocubes Phys. Chem. Chem. Phys. 2015, 17, 21226– 21235 DOI: 10.1039/C4CP05217J
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Seh, Z. W.; Liu, S.; Zhang, S. Y.; Bharathi, M. S.; Ramanarayan, H.; Low, M.; Shah, K. W.; Zhang, Y. W.; Han, M. Y. Anisotropic Growth of Titania onto Various Gold Nanostructures: Synthesis, Theoretical Understanding, and Optimization for Catalysis Angew. Chem., Int. Ed. 2011, 50, 10140– 10143 DOI: 10.1002/anie.201104943
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Anisotropic Growth of Titania onto Various Gold Nanostructures: Synthesis, Theoretical Understanding, and Optimization for Catalysis
Seh, Zhi Wei; Liu, Shuhua; Zhang, Shuang-Yuan; Bharathi, M. S.; Ramanarayan, H.; Low, Michelle; Shah, Kwok Wei; Zhang, Yong-Wei; Han, Ming-Yong
Angewandte Chemie, International Edition (2011), 50 (43), 10140-10143, S10140/1-S10140/10CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Anisotropic growth of titania various gold nanostructures, synthesis, theor. understanding, and optimization for catalysis are discussed.
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Lin, X. D.; Uzayisenga, V.; Li, J. F.; Fang, P. P.; Wu, D. Y.; Ren, B.; Tian, Z. Q. Synthesis of Ultrathin and Compact Au@MnO₂ Nanoparticles for Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy (SHINERS) J. Raman Spectrosc. 2012, 43, 40– 45 DOI: 10.1002/jrs.3007
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Synthesis of ultrathin and compact Au@MnO2 nanoparticles for shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS)
Lin, Xiao-Dong; Uzayisenga, Viviane; Li, Jian-Feng; Fang, Ping-Ping; Wu, De-Yin; Ren, Bin; Tian, Zhong-Qun
Journal of Raman Spectroscopy (2012), 43 (1), 40-45CODEN: JRSPAF; ISSN:0377-0486. (John Wiley & Sons Ltd.)
Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) based on Au@SiO2 or Au@Al2O3 nanoparticles (NPs) shows great potential to break the long-standing limitations of substrate and surface generality of surface-enhanced Raman scattering (SERS). However, the shell of SiO2 or Al2O3 can easily be dissolved in alk. media, which limits the applications of SHINERS in alk. systems. Besides that, the synthesis of Au@SiO2 NPs can be further simplified and Au@Al2O3 NPs be replaced by other NPs that are more amenable for mass prodn. In an attempt to make SHINERS NPs available in any systems practically, we report the synthesis of ultrathin and compact Au@MnO2 NPs. The shell thickness of MnO2 can be controlled down to about 1.2 nm without any pinhole. SHINERS based on such Au@MnO2 NPs exhibits much higher Raman enhancement effect than Au@SiO2 NPs and can be applied in alk. systems in which Au@SiO2 or Au@Al2O3 NPs cannot be applied. Copyright © 2011 John Wiley & Sons, Ltd.
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Sun, X.; Li, Y. Ag@C Core/Shell Structured Nanoparticles: Controlled Synthesis, Characterization, and Assembly Langmuir 2005, 21, 6019– 6024 DOI: 10.1021/la050193+
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Ag@C Core/Shell Structured Nanoparticles: Controlled Synthesis, Characterization, and Assembly
Sun, Xiaoming; Li, Yadong
Langmuir (2005), 21 (13), 6019-6024CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
Silver nanoparticles with tunable sizes were encapsulated in a carbonaceous shell through a green wet chem. route-the catalyzed dehydration of glucose under hydrothermal condition. In this one-pot synthesis, glucose was used as the reducing agent to react with Ag+ or Ag(NH3)2+, and it also served as the source of carbonaceous shells. The effects of hydrothermal temp., time, and the concns. of reagents on formation of the final nanostructures were systematically studied. The presence of competitive mols. poly(vinyl pyrrolidone) was able to relieve the carbonization process, to incorporate themselves into carbonaceous shell, and to make the carbonaceous shell colorless. All these approaches provided diverse means to tailor the Ag@C nanostructures. By evapn. of the solvents gradually in a moist atm., the monodispersed nanoparticles could self-assemble into arrays. TEM, SEM, and UV-vis extinction spectra and surface-enhanced Raman spectra were used to characterize the core/shell nanostructures. These Ag@C core/shell nanoparticles have hydrophilic, org.-group-loaded surfaces and characteristic optical properties, which indicated their promising applications in optical nanodevices and biochem.
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Formo, E. V.; Wu, Z.; Mahurin, S. M.; Dai, S. In Situ High Temperature Surface Enhanced Raman Spectroscopy for the Study of Interface Phenomena: Probing a Solid Acid on Alumina J. Phys. Chem. C 2011, 115, 9068– 9073 DOI: 10.1021/jp1119525
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In situ high temperature surface enhanced Raman spectroscopy for the study of interface phenomena: probing a solid acid on alumina
Formo, Eric V.; Wu, Zili; Mahurin, Shannon M.; Dai, Sheng
Journal of Physical Chemistry C (2011), 115 (18), 9068-9073CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
Herein, the authors use surface enhanced Raman spectroscopy (SERS) for the in situ analyses of catalyst structure while operating at elevated temps. in various atms. To accomplish this, robust SERS substrates were generated by depositing an ultrathin protective coating of alumina on top of Ag nanowires (NWs) via at. layer deposition (ALD). In situ studies were then conducted by analyzing the effects of heating a solid acid, phosphotungstic acid (PTA), on the alumina surface in either an oxygen or hydrogen environment at temps. up to 400°. The distance-dependent decay of the enhancement factor of the SERS signal from the underlying NWs allowed one to probe with great detail the interfacial region between the PTA and the alumina surface. The ability to analyze the area closest to the alumina surface was further confirmed by assembling vanadia onto the substrate and monitoring the intensity differences between the V-O-Al and outer V=O bonds.
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Buurmans, I. L. C.; Weckhuysen, B. M. Heterogeneities of Individual Catalyst Particles in Space and Time as Monitored by Spectroscopy Nat. Chem. 2012, 4, 873– 886 DOI: 10.1038/nchem.1478
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Heterogeneities of individual catalyst particles in space and time as monitored by spectroscopy
Buurmans, Inge L. C.; Weckhuysen, Bert M.
Nature Chemistry (2012), 4 (11), 873-886CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)
A review. Recent years have witnessed the introduction of spatiotemporal spectroscopy for the characterization of catalysts at work at previously unattainable resoln. and sensitivity. They have revealed that heterogeneous catalysts are more heterogeneous than often expected. Dynamic changes in the nature of active sites, such as their distribution and accessibility, occur both between and within particles. Scientists now have micro- and nanospectroscopic methods at hand to improve the understanding of catalyst heterogeneities and exploit them in catalyst design. Here we review the latest developments within this lively field. The trends include detection of single particles or mols., super-resoln. imaging, the transition from two- to three-dimensional imaging, selective staining, integration of spectroscopy with electron microscopy or scanning probe methods, and measuring under realistic reaction conditions. Such exptl. approaches change the hitherto somewhat static picture of heterogeneous catalysis into one that acknowledges that catalysts behave almost like living objects - explaining why many characterization methods from the life sciences are being incorporated into catalysis research.
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Harvey, C. E.; van Schrojenstein Lantman, E. M.; Mank, A. J. G.; Weckhuysen, B. M. An Integrated AFM-Raman Instrument for Studying Heterogeneous Catalytic Systems: A First Showcase Chem. Commun. 2012, 48, 1742– 1744 DOI: 10.1039/c2cc15939b
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106
Kumar, N.; Mignuzzi, S.; Su, W.; Roy, D. Tip-Enhanced Raman Spectroscopy: Principles and Applications EPJ. Technol. Instrum. 2015, 2, 1– 23 DOI: 10.1140/epjti/s40485-015-0019-5
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Domke, K. F.; Pettinger, B. In Situ Discrimination between Axially Complexed and Ligand-Free Co Porphyrin on Au (111) with Tip-Enhanced Raman Spectroscopy ChemPhysChem 2009, 10, 1794– 1798 DOI: 10.1002/cphc.200900182
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Singh, P.; Deckert-Gaudig, T.; Schneidewind, H.; Kirsch, K.; van Schrojenstein Lantman, E. M.; Weckhuysen, B. M.; Deckert, V. Differences in Single and Aggregated Nanoparticle Plasmon Spectroscopy Phys. Chem. Chem. Phys. 2015, 17, 2991– 2995 DOI: 10.1039/C4CP04850D
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Sun, M.; Zhang, Z.; Zheng, H.; Xu, H. In-Situ Plasmon-Driven Chemical Reactions Revealed by High Vacuum Tip-Enhanced Raman Spectroscopy Sci. Rep. 2012, 2, 1– 4 DOI: 10.1038/srep00647
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Zhang, Z.; Chen, L.; Sun, M.; Ruan, P.; Zheng, H.; Xu, H. Insights into the Nature of Plasmon-Driven Catalytic Reactions Revealed by HV-TERS Nanoscale 2013, 5, 3249– 3252 DOI: 10.1039/c3nr00352c
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Insights into the nature of plasmon-driven catalytic reactions revealed by HV-TERS
Zhang, Zhenglong; Chen, Li; Sun, Mengtao; Ruan, Panpan; Zheng, Hairong; Xu, Hongxing
Nanoscale (2013), 5 (8), 3249-3252CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
The nature of plasmon-driven chem. reactions is exptl. investigated using high vacuum tip-enhanced Raman spectroscopy (HV-TERS). It is revealed that the coupling between the tip and the substrate can produce intense plasmon resonance, which then decays to produce sufficient hot electrons and thus catalyzes the chem. reaction. The photoelectron emission from the laser illuminated silver substrate alone cannot drive the reaction.
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Kumar, N.; Stephanidis, B.; Zenobi, R.; Wain, A. J.; Roy, D. Nanoscale Mapping of Catalytic Activity Using Tip-Enhanced Raman Spectroscopy Nanoscale 2015, 7, 7133– 7137 DOI: 10.1039/C4NR07441F
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Nanoscale mapping of catalytic activity using tip-enhanced Raman spectroscopy
Kumar, N.; Stephanidis, B.; Zenobi, R.; Wain, A. J.; Roy, D.
Nanoscale (2015), 7 (16), 7133-7137CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
Chem.mapping of a photocatalytic reaction with nanoscale spatial resoln.is demonstrated for the first time using tip-enhanced Raman spectroscopy (TERS). An ultrathin alumina film applied to the Ag-coated TERS tip blocks catalytic interference while maintaining near-field electromagnetic enhancement, thus enabling spectroscopic imaging of catalytic activity on nanostructured Ag surfaces.
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Chaigneau, M.; Picardi, G.; Ossikovski, R. Surface Science Tip Enhanced Raman Spectroscopy Evidence for Amorphous Carbon Contamination on Gold Surfaces Surf. Sci. 2010, 604, 701– 705 DOI: 10.1016/j.susc.2010.01.018
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113
Ichimura, T.; Fujii, S.; Verma, P.; Yano, T.; Inouye, Y.; Kawata, S. Subnanometric Near-Field Raman Investigation in the Vicinity of a Metallic Nanostructure Phys. Rev. Lett. 2009, 102, 186101 DOI: 10.1103/PhysRevLett.102.186101
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Subnanometric Near-Field Raman Investigation in the Vicinity of a Metallic Nanostructure
Ichimura, Taro; Fujii, Shintaro; Verma, Prabhat; Yano, Takaaki; Inouye, Yasushi; Kawata, Satoshi
Physical Review Letters (2009), 102 (18), 186101/1-186101/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
We present a near-field Raman investigation in the subnanometric vicinity of a metallic nanotip, where the tip-sample distance is precisely controlled by our newly developed time-gated illumination technique. Using this scheme on an isolated carbon nanotube, we have profiled the spatial decay of evanescent light. We also investigated extremely short-ranged chem. and mech. interactions between the metal on the tip apex and the mols. of an adenine sample, which are observable only within the subnanometric vicinity of the tip. The results show a near-field Raman investigation with an accuracy of better than a few angstroms. Further, this shows strong promise for superhigh resoln. in optical microscopy based on this technique.
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Poborchii, V.; Tada, T.; Kanayama, T.; Geshev, P. Optimization of Tip Material and Shape for near-UV TERS in Si Structures J. Raman Spectrosc. 2009, 40, 1377– 1385 DOI: 10.1002/jrs.2417
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Yang, Z.; Aizpurua, J.; Xu, H. Electromagnetic Field Enhancement in TERS Configurations J. Raman Spectrosc. 2009, 40, 1343– 1348 DOI: 10.1002/jrs.2429
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Electromagnetic field enhancement in TERS configurations
Yang, Zhilin; Aizpurua, Javier; Xu, Hongxing
Journal of Raman Spectroscopy (2009), 40 (10), 1343-1348CODEN: JRSPAF; ISSN:0377-0486. (John Wiley & Sons Ltd.)
We use 3D finite-difference time domain (3D-FDTD) simulations to investigate the field enhancement properties of tip-enhanced Raman scattering (TERS) to find optimal geometric parameters of the metal tip and the metal substrate under certain excitation wavelengths with side illumination. The simulation results show that plasmon coupling effects between the metal tip and the metal substrate play the key role in TERS enhancement, and the enhancement drops dramatically as the distance between the tip and the substrate increases. The spatial resoln. of TERS is mainly dependent on the radius of curvature of the tip end. A sharp tip with a small radius can dramatically increase the spatial resoln. of TERS. Increasing the tip-substrate distance or changing the metallic substrate into a dielec. substrate lowers the spatial resoln. The TERS enhancement dependence on the incident angle and polarization, the size of tip, as well as the compn. of the substrate is also discussed in detail.
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Etchegoin, P. G.; Le Ru, E. C.; Meyer, M. Evidence of Natural Isotopic Distribution from Single-Molecule SERS J. Am. Chem. Soc. 2009, 131, 2713– 2716 DOI: 10.1021/ja808934d
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Evidence of Natural Isotopic Distribution from Single-Molecule SERS
Etchegoin, Pablo G.; Le Ru, Eric C.; Meyer, Matthias
Journal of the American Chemical Society (2009), 131 (7), 2713-2716CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The authors report on the observation of the natural isotopic spread of C from single-mol. surface-enhanced Raman spectroscopy (SM-SERS). By choosing a dye mol. with a very localized Raman-active vibration in a cyano bond (C-N triple bond), the authors observe (in a SERS colloidal liq.) a small fraction of SM-SERS events where the frequency of the cyano mode is softened and in agreement with the effect of substituting 12C by the next most abundant isotope, 13C. This example adds another demonstration of single-mol. sensitivity in SERS through isotopic editing, which in this case is done not by artificial isotopic editing but rather by nature itself. It also highlights SERS as a unique spectroscopic tool that is capable of detecting an isotopic change in one atom of a single mol.
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Ledesma, C.; Yang, J.; Chen, D.; Holmen, A. Recent Approaches in Mechanistic and Kinetic Studies of Catalytic Reactions Using SSITKA Technique ACS Catal. 2014, 4, 4527– 4547 DOI: 10.1021/cs501264f
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Recent Approaches in Mechanistic and Kinetic Studies of Catalytic Reactions Using SSITKA Technique
Ledesma, Cristian; Yang, Jia; Chen, De; Holmen, Anders
ACS Catalysis (2014), 4 (12), 4527-4547CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
A review. One of the most useful techniques to obtain valuable information on catalyzed heterogeneous reactions at, or near to, mol. level is the Steady-State Isotopic Transient Kinetic Anal. (SSITKA). Kinetic parameters of catalyst-surface reaction intermediates, such as concn., site coverage, reactivity, and rate consts. can be obtained and processed to provide valuable information about the reaction mechanism. This technique has been extensively tested in a wide range of different surface-catalyzed reactions, where the influence of different parameters on the intermediates has been studied (i.e., supports, active phases, particle size, addn. of promoters). Progresses in the coupling of spectroscopic techniques and advanced modeling could greatly improve the understanding of the surface reaction mechanism and provide more reliable kinetic models. This review compiles the main goals achieved up to date in heterogeneous catalytic systems using SSITKA and analyzes the perspectives of this technique in the near future.
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Shen, H.; Zhou, X.; Zou, N.; Chen, P. Single-Molecule Kinetics Reveals a Hidden Surface Reaction Intermediate in Single-Nanoparticle Catalysis J. Phys. Chem. C 2014, 118, 26902– 26911 DOI: 10.1021/jp509507u
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Single-Molecule Kinetics Reveals a Hidden Surface Reaction Intermediate in Single-Nanoparticle Catalysis
Shen, Hao; Zhou, Xiaochun; Zou, Ningmu; Chen, Peng
Journal of Physical Chemistry C (2014), 118 (46), 26902-26911CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
Detecting and characterizing reaction intermediates is not only important and powerful for elucidating reaction mechanisms but also challenging in general because of the low populations of intermediates in a reaction mixt. Studying surface reaction intermediates in heterogeneous catalysis presents addnl. challenges, esp. the ubiquitous structural heterogeneity among the catalyst particles and the accompanying polydispersion in reaction kinetics. Here we use single-mol. fluorescence microscopy to study two complementary types of Au nanocatalysts-mesoporous-silica-coated Au nanorods (i.e., Au@mSiO2 nanorods) and bare 5.3 nm pseudospherical Au nanoparticles-at the single-particle, single-turnover resoln. in catalyzing the oxidative deacetylation of amplex red by H2O2, a synthetically relevant and increasingly important probe reaction. For both nanocatalysts, the distributions of the microscopic reaction time from a single catalyst particle clearly reveal a kinetic intermediate, which is hidden when the data are averaged over many particles or only the time-averaged turnover rates are examd. for a single particle. This intermediate is further resolvable by single-turnover kinetics at the subparticle level. Detailed single-mol. kinetic anal. leads to a quant. reaction mechanism and supports that the intermediate is likely a surface-adsorbed one-electron-oxidized amplex red radical. The quantitation of kinetic parameters further allows for the evaluation of the large reactivity inhomogeneity among the individual nanorods and pseudospherical nanoparticles, and for Au@mSiO2 nanorods, it uncovers their size-dependent reactivity in catalyzing the first one-electron oxidn. of amplex red to the radical. Such single-particle, single-mol. kinetic studies are expected to be broadly useful for dissecting reaction kinetics and mechanisms.
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van Schrojenstein Lantman, E. M.; Gijzeman, O. L. J.; Mank, A. J. G.; Weckhuysen, B. M. Investigation of the Kinetics of a Surface Photocatalytic Reaction in Two Dimensions with Surface-Enhanced Raman Scattering ChemCatChem 2014, 6, 3342– 3346 DOI: 10.1002/cctc.201402647
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Investigation of the Kinetics of a Surface Photocatalytic Reaction in Two Dimensions with Surface-enhanced Raman Scattering
van Schrojenstein Lantman, Evelien M.; Gijzeman, Onno L. J.; Mank, Arjan J. G.; Weckhuysen, Bert M.
ChemCatChem (2014), 6 (12), 3342-3346CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)
Heterogeneous catalysis is a surface phenomenon. Yet, though the catalysis itself takes place on surfaces, the reactants and products rapidly take the form of another phys. state, as either a liq. or a gas. Catalytic reactions within a self-assembled monolayer are confined within two dimensions, as the mols. involved do not leave the surface. Surface-enhanced Raman spectroscopy is an ideal technique to probe these self-assembled monolayers as it gives mol. information in a measured vol. limited to the surface. We show how surface-enhanced Raman spectroscopy can be used to det. the reaction kinetics of a two-dimensional reaction. As a proof of principle, we study the photocatalytic redn. of p-nitrothiophenol. A study of the reaction rate and diln. effects leads to the conclusion that a dimerization must take place as one of the reaction steps.
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Yampolsky, S.; Fishman, D. A.; Dey, S.; Hulkko, E.; Banik, M.; Potma, E. O.; Apkarian, V. A. Seeing a Single Molecule Vibrate through Time-Resolved Coherent Anti-Stokes Raman Scattering Nat. Photonics 2014, 8, 650– 656 DOI: 10.1038/nphoton.2014.143
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Seeing a single molecule vibrate through time-resolved coherent anti-Stokes Raman scattering
Yampolsky, Steven; Fishman, Dmitry A.; Dey, Shirshendu; Hulkko, Eero; Banik, Mayukh; Potma, Eric O.; Apkarian, Vartkess A.
Nature Photonics (2014), 8 (8), 650-656CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)
The motion of chem. bonds within mols. can be obsd. in real time in the form of vibrational wave packets prepd. and interrogated through ultrafast nonlinear spectroscopy. Such nonlinear optical measurements are commonly performed on large ensembles of mols. and, as such, are limited to the extent that ensemble coherence can be maintained. Here, we describe vibrational wave packet motion on single mols., recorded through time-resolved, surface-enhanced, coherent anti-Stokes Raman scattering. The sensitivity required to detect the motion of a single mol. under ambient conditions is achieved by equipping the mol. with a dipolar nano-antenna (a gold dumbbell). In contrast with measurements in ensembles, the vibrational coherence on a single mol. does not undergo pure dephasing. It develops phase fluctuations with characteristic statistics. We present the time evolution of discretely sampled statistical states, and highlight the unique information content in the characteristic, early-time probability distribution function of the signal.
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Pozzi, E. A.; Sonntag, M. D.; Jiang, N.; Chiang, N.; Seideman, T.; Hersam, M. C.; Van Duyne, R. P. Ultrahigh Vacuum Tip-Enhanced Raman Spectroscopy with Picosecond Excitation J. Phys. Chem. Lett. 2014, 5, 2657– 2661 DOI: 10.1021/jz501239z
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Ultrahigh Vacuum Tip-Enhanced Raman Spectroscopy with Picosecond Excitation
Pozzi, Eric A.; Sonntag, Matthew D.; Jiang, Nan; Chiang, Naihao; Seideman, Tamar; Hersam, Mark C.; Van Duyne, Richard P.
Journal of Physical Chemistry Letters (2014), 5 (15), 2657-2661CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
Tip-enhanced Raman spectroscopy (TERS) provides chem. information about adsorbates with nanoscale spatial resoln., but developments are still required to incorporate ultrafast temporal resoln. In this Letter, a reliable TER signal of rhodamine 6G (R6G) using picosecond (ps)-pulsed excitation can be obtained in ultrahigh vacuum (UHV). In contrast to previous observation of irreversible signal loss in ambient TERS, the UHV environment decreases irreversible signal degrdn. As a complement to the TERS expts., the authors examd. the rate of surface-enhanced Raman (SER) signal decay under picosecond irradn. and found that it is also slowed in UHV compared to that in ambient. Signal decay kinetics suggest that the predominant mechanism responsible for signal loss in ps SERS of R6G is surface diffusion. Both diffusive and reactive phenomena can lead to pulsed excitation TER signal loss, and a UHV environment is advantageous in either scenario.
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Zhang, Y.; Walkenfort, B.; Yoon, J. H.; Schlücker, S.; Xie, W. Gold and Silver Nanoparticle Monomers Are Non-SERS-Active: A Negative Experimental Study with Silica-Encapsulated Raman-Reporter-Coated Metal Colloids Phys. Chem. Chem. Phys. 2015, 17, 21120– 21126 DOI: 10.1039/C4CP05073H
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Gold and silver nanoparticle monomers are non-SERS-active: a negative experimental study with silica-encapsulated Raman-reporter-coated metal colloids
Zhang, Yuying; Walkenfort, Bernd; Yoon, Jun Hee; Schluecker, Sebastian; Xie, Wei
Physical Chemistry Chemical Physics (2015), 17 (33), 21120-21126CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
Noble metal nanoparticles (NPs) are the most commonly employed plasmonic substrates in surface-enhanced Raman scattering (SERS) expts. Computer simulations show that monomers of Ag and Au nanocrystals (spherical NPs) do not exhibit a notable plasmonic enhancement, i.e., they are essentially non-SERS-active. In expts., SERS enhanced by spherical NP colloids was frequently reported. This implies that the monomers do not have strong SERS activity, but detectable enhancement should more or less be there. Because of the gap between theory and practice, it is important to demonstrate exptl. how SERS-active the metal colloid actually is and, in case a SERS signal is obsd., where it originates from. The aggregation of the colloid, induced by high centrifugal forces in washing steps or due to a harsh ionic environment of the suspension medium, should be controlled since it is the very high SERS activity of NP clusters which dominates the overall SERS signal of the colloid. The authors report here the exptl. evaluation of the SERS activity of 80 nm Au and Ag NP monomers. Instead of showing fancy nanostructures and super SERS enhancement, the method on how to obtain neg. exptl. data is presented. In this approach, no SERS signal was obtained from the colloid with a Raman reporter on the metal surface when the NPs were encapsulated carefully within a thick SiO2 shell. Without SiO2 encapsulation, if a very low centrifugation speed is used for the washing steps, only a negligible SERS signal can be detected even at very high NP concns. But strong SERS signals can be detected when the NPs are suspended in acidic solns. Au and Ag NP monomers essentially exhibit no SERS activity of practical relevance.
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Cite this: J. Phys. Chem. Lett. 2016, 7, 8, 1570–1584

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Abstract
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Figure 1
Figure 1. Strongest EFs arise from hot spots, which are produced by gap-mode plasmons that emerge between closely spaced plasmonic particles or tip–surface interactions where the plasmons overlap. (a) The Raman signal EF can reach theoretical values of 10⁸ for dimer gold nanoparticles under 559 nm laser irradiance (40) and (b) 10¹¹ for a sharp gold tip–gold surface interaction under 633 nm laser irradiance. (40) (c) The electric field is at its strongest when the particles touch and rapidly reduces to a negligible value when the particles are more than 15 nm away from each other. (d) This can be observed in the SERS spectra of adsorbed ammonium salt of pyrene on Ag@SiO₂ spheres. (e) Plot of SERS EF versus distance between the particles. (41) Reprinted with permission from ref 40. Copyright 2008 Royal Society of Chemistry. Reprinted from ref 41. Copyright 2012 American Chemical Society.
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Figure 2
Figure 2. (a) Nano v-grooves, (46) (b) artist’s impression of nanopyramids, (46) (c) nanowires and nanogaps with cross section in inset, (45) (d) histogram of analytical enhancement factor (AEF) on a nanowire–nanogap substrate, (45) (e) −0.2 V and (f) −0.5 V spectro-electrogram of MPY/hemin modified gold nanowire electrodes with the Fe²⁺ and Fe³⁺ bands indicated. (48) Reprinted from refs 45, 46, and 48. Copyright 2013, 2010, and 2015, respectively, American Chemical Society.
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Figure 3
Figure 3. (a) Schematic diagram of the formation of hot electrons and holes in silver nanoparticles, which are able to catalyze both oxidative and reductive reactions. (79) (b) Possible reactions occurring during the chemical reduction of 4-NTP by NaBH₄ over gold nanoparticles. (c) NMF-calculated SERS spectra of the three pure components including their assignment to the three molecular species 4-NTP (blue), 4,4′-DMAB (green), and 4-ATP (red). (98) (d) Raw SERS spectra of the reduction of 4-NTP to 4-ATP over Au/Pt/Au catalysts, including DMAB-associated peaks for intermediate volumes of NaBH₄ added, corresponding to the calculated spectra from panel c. (98) Reprinted with permission from ref 79. Copyright 2012 Royal Society of Chemistry. Reprinted from ref 98. Copyright 2011 American Chemical Society.
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Figure 4
Figure 4. Advantages of SHINs over bare gold nanoparticles. (a) SHINs prevent plasmon-driven reactions. SERS spectra collected from 4-ATP adsorbed on 80 nm gold particles, 80 nm gold nanoparticles covered with 5 nm gold particles, and 80 nm SHINs covered with 5 nm gold particles. DMAB is not observed when SHINs are implemented. (67) Adapted from ref 67. Copyright 2013 American Chemical Society. (b) SERS EF calculated for a variety of silver nanocubes: bare (I, red) and SiO₂-coated cubes using different methods (II–V, blue). All SiO₂-coated nanocubes show increased EFs compared to bare silver nanocubes. (99) Adapted with permission from ref 99. Copyright 2015 Royal Society of Chemistry. (c) UV–vis absorption spectra of gold nanoparticles at elevated temperatures indicate that their LSPR shifts above temperatures of 100 °C. (94) (d) UV–vis absorption spectra of gold nanoparticles coated with 1 nm alumina at elevated temperatures indicate that stability is maintained up to 400 °C. (94) Adapted from ref 94. Copyright 2007 American Chemical Society. (e) SHINs (green) could potentially serve as a support for many other catalysts (purple spheres). Because the electric field is stronger (red) at the surface of the SHIN, it is expected that the catalyst–support interface can be characterized.
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Figure 5
Figure 5. (a, b) SHINERS spectra of Pt{hkl} single crystals immersed in 0.1 M EP/0.1 M HClO₄ recorded under hydrogen evolution conditions (−0.1 V). (c) Schematic depiction of the half-hydrogenated state (HHS) intermediate. (d) Calculated structure of EP adsorbed in the μ₂(C,O) configuration. (e) Calculated structure of HHS at a Pt{221} surface. Reprinted from ref 95. Copyright 2016 American Chemical Society.
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Figure 6
Figure 6. (a) AFM topography image of the Ag catalyst substrate. (b) TERS map of the area marked by the dashed rectangle in panel a showing signal intensities of a DMAB-associated band at 1142 cm^–1. (c) Near-field spectra measured at the positions marked in panel b. (d) Intensity profile along the dotted line marked in panel b showing the spatial resolution of the TERS map using a fitted Gaussian curve (red) to be 20 nm. (111) Reprinted with permission from ref 111. Copyright 2015 Royal Society of Chemistry.
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Figure 7
Figure 7. PCA used to obtain kinetic data with reduced noise in SERS experiments. (Left) The conventional method to obtain kinetic data is to plot a peak area over time. (Middle) Spectral fluctuations can be removed from the spectrum with a PCA time filter, after which a two-component MCR can further clear up the kinetic data. The kinetic data is now analyzed over full spectra instead of over single peaks, making it less prone to shifts in band positions. (Right) The discarded data after the PCA time filter can be analyzed with MCR to find possible intermediate structures. (30) Adapted with permission from ref 30. Copyright 2015 Wiley-VCH.
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  Wachs, I. E.; Roberts, C. A. Monitoring Surface Metal Oxide Catalytic Active Sites with Raman Spectroscopy Chem. Soc. Rev. 2010, 39, 5002– 5017 DOI: 10.1039/c0cs00145g
  13
  Monitoring surface metal oxide catalytic active sites with Raman spectroscopy
  Wachs, Israel E.; Roberts, Charles A.
  Chemical Society Reviews (2010), 39 (12), 5002-5017CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
  A review. The mol. aspect of the Raman vibrational selection rules allows for the mol. structural and reactivity detns. of metal oxide catalytic active sites in all types of oxide catalyst systems (supported metal oxides, zeolites, layered hydroxides, polyoxometalates (POMs), bulk pure metal oxides, bulk mixed oxides and mixed oxide solid solns.). The mol. structural and reactivity detns. of metal oxide catalytic active sites are greatly facilitated by the use of isotopically labeled mols. The ability of Raman spectroscopy to (i) operate in all phases (liq., solid, gas and their mixts.), (ii) operate over a very wide temp. (-273 to >1000°) and pressure (UHV to »100 atm) range, and (iii) provide mol. level information about metal oxides makes Raman spectroscopy the most informative characterization technique for understanding the mol. structure and surface chem. of the catalytic active sites present in metal oxide heterogeneous catalysts. The recent use of hyphenated Raman spectroscopy instrumentation (e.g., Raman-IR, Raman-UV-vis, Raman-EPR) and the operando Raman spectroscopy methodol. (e.g., Raman-MS and Raman-GC) is allowing for the establishment of direct structure-activity/selectivity relationships that will have a significant impact on catalysis science in this decade. Consequently, this crit. review will show the growth in the use of Raman spectroscopy in heterogeneous catalysis research, for metal oxides as well as metals, is poised to continue to exponentially grow in the coming years.
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14. 14
  Bañares, M. A.; Mestl, G. Structural Characterization of Operating Catalysts by Raman Spectroscopy Adv. Catal. 2009, 52, 43– 128 DOI: 10.1016/S0360-0564(08)00002-3
  There is no corresponding record for this reference.
15. 15
  Cheng, J.-X.; Xie, X. S. Coherent Anti-Stokes Raman Scattering Microscopy: Instrumentations, Theory and Applications J. Phys. Chem. B 2004, 108, 827– 840 DOI: 10.1021/jp035693v
  There is no corresponding record for this reference.
16. 16
  Smith, E.; Dent, G. Modern Raman Spectroscopy—A Practical Approach, 1st ed.; John Wiley & Sons, Ltd: Chichester, England, 2005.
  There is no corresponding record for this reference.
17. 17
  Schlücker, S. Surface-Enhanced Raman Spectroscopy: Concepts and Chemical Applications Angew. Chem., Int. Ed. 2014, 53, 4756– 4795 DOI: 10.1002/anie.201205748
  17
  Surface-Enhanced Raman Spectroscopy: Concepts and Chemical Applications
  Schluecker, Sebastian
  Angewandte Chemie, International Edition (2014), 53 (19), 4756-4795CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A review. Surface-enhanced Raman scattering (SERS) has become a mature vibrational spectroscopic technique during the last decades and the no. of applications in the chem., material, and in particular life sciences is rapidly increasing. This Review explains the basic theory of SERS in a brief tutorial and-based on original results from recent research-summarizes fundamental aspects necessary for understanding SERS and provides examples for the prepn. of plasmonic nanostructures for SERS. Chem. applications of SERS are the centerpiece of this Review. They cover a broad range of topics such as catalysis and spectroelectrochem., single-mol. detection, and (bio)anal. chem.
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18. 18
  Tian, Z. Q.; Ren, B.; Wu, D. Y. Surface-Enhanced Raman Scattering: From Nobel to Transition Metals and From Rough Surfaces to Ordered Nanostructures J. Phys. Chem. B 2002, 106, 9463– 9483 DOI: 10.1021/jp0257449
  There is no corresponding record for this reference.
19. 19
  Xie, W.; Schlücker, S. Rationally Designed Multifunctional Plasmonic Nanostructures for Surface-Enhanced Raman Spectroscopy: A Review Rep. Prog. Phys. 2014, 77, 116502 DOI: 10.1088/0034-4885/77/11/116502
  19
  Rationally designed multifunctional plasmonic nanostructures for surface-enhanced Raman spectroscopy: a review
  Xie, Wei; Schluecker, Sebastian
  Reports on Progress in Physics (2014), 77 (11), 116502/1-116502/22CODEN: RPPHAG; ISSN:0034-4885. (IOP Publishing Ltd.)
  Rationally designed multifunctional plasmonic nanostructures efficiently integrate two or more functionalities into a single entity, for example, with both plasmonic and catalytic activity. This review article is focused on their synthesis and use in surface-enhanced Raman scattering (SERS) as a mol. spectroscopic technique with high sensitivity, fingerprint specificity, and surface selectivity. After a short tutorial on the fundamentals of Raman scattering and SERS in particular, applications ranging from chem. (heterogeneous catalysis) to biol. and medicine (diagnostics/imaging, therapy) are summarized.
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20. 20
  Zhang, Y.; Zhen, Y.-R.; Neumann, O.; Day, J. K.; Nordlander, P.; Halas, N. J. Coherent Anti-Stokes Raman Scattering with Single-Molecule Sensitivity Using a Plasmonic Fano Resonance Nat. Commun. 2014, 5, 4424 DOI: 10.1038/ncomms5424
  20
  Coherent anti-Stokes Raman scattering with single-molecule sensitivity using a plasmonic Fano resonance
  Zhang, Yu; Zhen, Yu-Rong; Neumann, Oara; Day, Jared K.; Nordlander, Peter; Halas, Naomi J.
  Nature Communications (2014), 5 (), 4424CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
  Plasmonic nanostructures are of particular interest as substrates for the spectroscopic detection and identification of individual mols. Single-mol. sensitivity Raman detection has been achieved by combining resonant mol. excitation with large electromagnetic field enhancements experienced by a mol. assocd. with an interparticle junction. Detection of mols. with extremely small Raman cross-sections (∼10-30 cm2 sr-1), however, has remained elusive. Here we show that coherent anti-Stokes Raman spectroscopy (CARS), a nonlinear spectroscopy of great utility and potential for mol. sensing, can be used to obtain single-mol. detection sensitivity, by exploiting the unique light harvesting properties of plasmonic Fano resonances. The CARS signal is enhanced by ∼11 orders of magnitude relative to spontaneous Raman scattering, enabling the detection of single mols., which is verified using a statistically rigorous bi-analyte method. This approach combines unprecedented single-mol. spectral sensitivity with plasmonic substrates that can be fabricated using top-down lithog. strategies.
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21. 21
  Hoffmann, F. M. Infrared Reflection-Absorption Spectroscopy of Adsorbed Molecules Surf. Sci. Rep. 1983, 3, 107– 192 DOI: 10.1016/0167-5729(83)90001-8
  21
  Infrared reflection-absorption spectroscopy of adsorbed molecules
  Hoffmann, Friedrich M.
  Surface Science Reports (1983), 3 (2-3), 107-92CODEN: SSREDI; ISSN:0167-5729.
  A review with 202 refs.
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22. 22
  Rupprechter, G. Sum Frequency Generation and Polarization-Modulation Infared Reflection Absorption Spectrosocpy of Functioning Model Catalysts from Ultrahigh Vacuum to Ambient Pressure Adv. Catal. 2007, 51, 133– 263 DOI: 10.1016/S0360-0564(06)51004-1
  There is no corresponding record for this reference.
23. 23
  Shen, Y. R. Surface Properties Probed by Second-Harmonic and Sum-Frequency Generation Nature 1989, 337, 519– 525 DOI: 10.1038/337519a0
  23
  Surface properties probed by second-harmonic and sum-frequency generation
  Shen, Y. R.
  Nature (London, United Kingdom) (1989), 337 (6207), 519-25CODEN: NATUAS; ISSN:0028-0836.
  A review on optical 2nd-harmonic generation and IR-visible light sum-frequency generation studies of surfaces and interfaces. Combined with ultrashort laser pulses, these methods can be used to study surface dynamics and reactions with subpicosecond time resoln. Sixty-one refs.
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24. 24
  Han, H. L.; Melaet, G.; Alayoglu, S.; Somorjai, G. A. In-situ Microscopy and Spectroscopy Applied to Surfaces at Work ChemCatChem 2015, 7, 3625– 3628 DOI: 10.1002/cctc.201500642
  There is no corresponding record for this reference.
25. 25
  Somorjai, G. A.; Frei, H.; Park, J. Y. Advancing the Frontiers in Nanocatalysis, Biointerfaces and Renewable Energy Conversion by Innovations of Surface Techniques J. Am. Chem. Soc. 2009, 131, 16589– 16605 DOI: 10.1021/ja9061954
  There is no corresponding record for this reference.
26. 26
  Bratlie, K. M.; Montano, M. O.; Flores, L. D.; Paajanen, M.; Somorjai, G. A. Sum Frequency Generation Vibrational Spectroscopic and High-Pressure Scanning Tunneling Microscopic Studies of Benzene Hydrogenation on Pt(111) J. Am. Chem. Soc. 2006, 128, 12810– 12816 DOI: 10.1021/ja0626032
  26
  Sum Frequency Generation Vibrational Spectroscopic and High-Pressure Scanning Tunneling Microscopic Studies of Benzene Hydrogenation on Pt(111)
  Bratlie, Kaitlin M.; Montano, Max O.; Flores, Lucio D.; Paajanen, Matti; Somorjai, Gabor A.
  Journal of the American Chemical Society (2006), 128 (39), 12810-12816CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Sum frequency generation (SFG) vibrational spectroscopy and high-pressure scanning tunneling microscopy (HP-STM) have been used in combination for the first time to study a catalytic reaction. These techniques have been able to identify surface intermediates in situ during benzene hydrogenation on a Pt(111) single-crystal surface at Torr pressures. In a background of 10 Torr of benzene, STM is able to image small ordered regions corresponding to the c(2√3 × 3)rect structure in which each mol. is chemisorbed at a bridge site. In addn., individual benzene mols. are also obsd. between the ordered regions. These individual mols. are assumed to be physisorbed benzene on the basis of the SFG results showing both chemisorbed and physisorbed mols. The surface becomes too mobile to image upon addn. of hydrogen but is detd. to have physisorbed and chemisorbed benzene present by SFG. It was spectroscopically detd. that heating the platinum surface after poisoning with CO displaces benzene mols. The high-coverage pure CO structure of (√19 × √19)R23.4° imaged with STM is a verification of spectroscopic measurements.
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27. 27
  Zhang, R.; Zhang, Y.; Dong, Z. C.; Jiang, S.; Zhang, C.; Chen, L. G.; Zhang, L.; Liao, Y.; Aizpurua, J.; Luo, Y. Chemical Mapping of a Single Molecule by Plasmon-Enhanced Raman Scattering Nature 2013, 498, 82– 86 DOI: 10.1038/nature12151
  27
  Chemical mapping of a single molecule by plasmon-enhanced Raman scattering
  Zhang, R.; Zhang, Y.; Dong, Z. C.; Jiang, S.; Zhang, C.; Chen, L. G.; Zhang, L.; Liao, Y.; Aizpurua, J.; Luo, Y.; Yang, J. L.; Hou, J. G.
  Nature (London, United Kingdom) (2013), 498 (7452), 82-86CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
  Visualizing individual mols. with chem. recognition is a longstanding target in catalysis, mol. nanotechnol. and biotechnol. Mol. vibrations provide a valuable fingerprint' for such identification. Vibrational spectroscopy based on tip-enhanced Raman scattering allows us to access the spectral signals of mol. species very efficiently via the strong localized plasmonic fields produced at the tip apex. However, the best spatial resoln. of the tip-enhanced Raman scattering imaging is still limited to 3-15 nm, which is not adequate for resolving a single mol. chem. Here we demonstrate Raman spectral imaging with spatial resoln. below one nanometer, resolving the inner structure and surface configuration of a single mol. This is achieved by spectrally matching the resonance of the nanocavity plasmon to the mol. vibronic transitions, particularly the downward transition responsible for the emission of Raman photons. This matching is made possible by the extremely precise tuning capability provided by scanning tunneling microscopy. Exptl. evidence suggests that the highly confined and broadband nature of the nanocavity plasmon field in the tunnelling gap is essential for ultrahigh-resoln. imaging through the generation of an efficient double-resonance enhancement for both Raman excitation and Raman emission. Our technique not only allows for chem. imaging at the single-mol. level, but also offers a new way to study the optical processes and photochem. of a single mol.
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28. 28
  Long, R.; Li, Y.; Song, L.; Xiong, Y. Coupling Solar Energy into Reactions: Materials Design for Surface Plasmon-Mediated Catalysis Small 2015, 11, 3873– 3889 DOI: 10.1002/smll.201403777
  28
  Coupling Solar Energy into Reactions: Materials Design for Surface Plasmon-Mediated Catalysis
  Long, Ran; Li, Yu; Song, Li; Xiong, Yujie
  Small (2015), 11 (32), 3873-3889CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A review. Enabled by surface plasmons, noble metal nanostructures can interact with and harvest incident light. As such, they may serve as unique media to generate heat, supply energetic electrons, and provide strong local electromagnetic fields for chem. reactions through different mechanisms. This solar-to-chem. pathway provides a new approach to solar energy use, alternative to conventional semiconductor-based photocatalysis. To provide readers with a clear picture of this newly recognized process, this review presents coupling solar energy into chem. reactions through plasmonic nanostructures. It starts with a brief introduction of surface plasmons in metallic nanostructures, followed by a demonstration of tuning plasmonic features by tailoring their phys. parameters. Owing to their tunable plasmonic properties, metallic materials offer a platform to trigger and drive chem. reactions at the nanoscale, as systematically overviewed. The design rules for plasmonic materials for catalytic applications are further outlined based on existing examples. At the end of this article, the challenges and opportunities for further development of plasmonic-mediated catalysis toward energy and environmental applications are discussed.
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29. 29
  van Schrojenstein Lantman, E. M.; Deckert-Gaudig, T.; Mank, A. J. G.; Deckert, V.; Weckhuysen, B. M. Catalytic Processes Monitored at the Nanoscale with Tip-Enhanced Raman Spectroscopy Nat. Nanotechnol. 2012, 7, 583– 586 DOI: 10.1038/nnano.2012.131
  29
  Catalytic processes monitored at the nanoscale with tip-enhanced Raman spectroscopy
  van Schrojenstein Lantman, Evelien M.; Deckert-Gaudig, Tanja; Mank, Arjan J. G.; Deckert, Volker; Weckhuysen, Bert M.
  Nature Nanotechnology (2012), 7 (9), 583-586CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
  Heterogeneous catalysts play a pivotal role in the chem. industry, but acquiring mol. insights into functioning catalysts remains a significant challenge. Recent advances in micro-spectroscopic approaches have allowed spatiotemporal information to be obtained on the dynamics of single active sites and the diffusion of single mols. However, these methods lack nanometer-scale spatial resoln. and/or require the use of fluorescent labels. Here, we show that time-resolved tip-enhanced Raman spectroscopy can monitor photocatalytic reactions at the nanoscale. We use a silver-coated at. force microscope tip to both enhance the Raman signal and to act as the catalyst. The tip is placed in contact with a self-assembled monolayer of p-nitrothiophenol mols. adsorbed on gold nanoplates. A photocatalytic redn. process is induced at the apex of the tip with green laser light, while red laser light is used to monitor the transformation process during the reaction. This dual-wavelength approach can also be used to observe other mol. effects such as monolayer diffusion.
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30. 30
  van Schrojenstein Lantman, E. M.; de Peinder, P.; Mank, A. J. G.; Weckhuysen, B. M. Separation of Time-Resolved Phenomena in Surface-Enhanced Raman Scattering of the Photocatalytic Reduction of p-Nitrothiophenol ChemPhysChem 2015, 16, 547– 554 DOI: 10.1002/cphc.201402709
  30
  Separation of Time-Resolved Phenomena in Surface-Enhanced Raman Scattering of the Photocatalytic Reduction of p-Nitrothiophenol
  van Schrojenstein Lantman, E. M.; de Peinder, P.; Mank, A. J. G.; Weckhuysen, B. M.
  ChemPhysChem (2015), 16 (3), 547-554CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Straightforward anal. of chem. processes on the nanoscale is difficult, as the measurement vol. is linked to a discrete no. of mols., ruling out any ensemble averaging over rotation and diffusion processes. Raman spectroscopy is sufficiently selective for monitoring chem. changes, but is not sufficiently sensitive to be applied directly. Surface-enhanced Raman spectroscopy (SERS) can be applied for studying reaction kinetics, but adds addnl. variability in the signal as the enhancement factor is not the same for every location. A novel chemometric method described here separates reaction kinetics from short-term variability, based on the lack of fit in a principal-component anal. We show that it is possible to study effects that occur on different time scales independently without data redn. using the photocatalytic redn. of p-nitrothiophenol as a showcase system. Using this approach a better description of the nanoscale reaction kinetics becomes available, while the short-term variations can be examd. sep. to examine reorientation and/or diffusion effects. It may even be possible to identify reaction intermediates through this approach. With only a limited no. of reactive mols. in the studied vol., an intermediate on a SERS hot spot may temporarily dominate the spectrum. Now such events can be easily sepd. from the bulk conversion process by making use of this chemometric method.
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31. 31
  Keller, E. L.; Brandt, N. C.; Cassabaum, A. A.; Frontiera, R. R. Ultrafast Surface-Enhanced Raman Spectroscopy Analyst 2015, 140, 4922– 4931 DOI: 10.1039/C5AN00869G
  31
  Ultrafast surface-enhanced Raman spectroscopy
  Keller, Emily L.; Brandt, Nathaniel C.; Cassabaum, Alyssa A.; Frontiera, Renee R.
  Analyst (Cambridge, United Kingdom) (2015), 140 (15), 4922-4931CODEN: ANALAO; ISSN:0003-2654. (Royal Society of Chemistry)
  A review. Ultrafast surface-enhanced Raman spectroscopy (SERS) with pico- and femtosecond time resoln. has the ability to elucidate the mechanisms by which plasmons mediate chem. reactions. Here the authors review three important technol. advances in these new methodologies, and discuss their prospects for applications in areas including plasmon-induced chem. and sensing at very low limits of detection. Surface enhancement, arising from plasmonic materials, was successfully incorporated with stimulated Raman techniques such as femtosecond stimulated Raman spectroscopy (FSRS) and coherent anti-Stokes Raman spectroscopy (CARS). These techniques are capable of time-resolved measurement on the femtosecond and picosecond time scale and can be used to follow the dynamics of mols. reacting near plasmonic surfaces. The potential application of ultrafast SERS techniques to probe plasmon-mediated processes, such as H2 dissocn. and solar steam prodn. are discussed. Addnl., the possibilities for high sensitivity SERS sensing using these stimulated Raman spectroscopies are discussed.
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32. 32
  Hu, K.; Li, D.; Cui, J.; Cao, Y.; Long, Y. In Situ Monitoring of Palladacycle-Mediated Carbonylation by Surface-Enhanced Raman Spectroscopy RSC Adv. 2015, 5, 97734– 97737 DOI: 10.1039/C5RA20292B
  32
  In situ monitoring of palladacycle-mediated carbonylation by surface-enhanced Raman spectroscopy
  Hu, Kai; Li, Da-Wei; Cui, Jing; Cao, Yue; Long, Yi-Tao
  RSC Advances (2015), 5 (118), 97734-97737CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)
  Palladium-catalyzed carbonylation has emerged as one of the most potential approaches for the synthesis of carbonyl-contg. mols., however, the understanding remains challenging in many reactions partly because of a lack of robust monitoring methods. Herein, authors report a novel surface-enhanced Raman spectroscopy (SERS) based strategy for the in situ monitoring of palladacycle-mediated carbonylation. The nanoplatforms integrated with SERS activity and reaction mediability were constructed through assembling new synthesized palladacycles (PCs) on the surface of gold nanoparticles. It was shown that, when carbon monoxide (CO) was introduced to the nanoplatform-contg. system as a C1 source, palladacycle-mediated carbonylation was initiated, and the SERS spectra of the nanoplatforms changed concomitantly. With this SERS spectrum variation, the reaction mechanism could be investigated facilely, and the corresponding reaction was found to follow a pseudo-first-order kinetics rate law based on the relationship between the relative ratiometric peak intensities of I1319/I1338 and the reaction time. Therefore, using the proposed SERS approach, the carbonylation process could be directly monitored in situ without tedious pretreatments.
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33. 33
  Joseph, V.; Engelbrekt, C.; Zhang, J.; Gernert, U.; Ulstrup, J.; Kneipp, J. Characterizing the Kinetics of Nanoparticle-Catalyzed Reactions by Surface-Enhanced Raman Scattering Angew. Chem., Int. Ed. 2012, 51, 7592– 7596 DOI: 10.1002/anie.201203526
  33
  Characterizing the Kinetics of Nanoparticle-Catalyzed Reactions by Surface-Enhanced Raman Scattering
  Joseph, Virginia; Engelbrekt, Christian; Zhang, Jingdong; Gernert, Ulrich; Ulstrup, Jens; Kneipp, Janina
  Angewandte Chemie, International Edition (2012), 51 (30), 7592-7596, S7592/1-S7592/4CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  We demonstrate that SERS can be used to study directly the kinetics of a catalytic reaction in situ. Our approach is novel by allowing the structural characterization of the reactant and product surface species in the reaction as well as investigating rate consts. in the same expt. This was possible by using sep. gold and platinum nanoparticles that were simultaneously attached to the same glass surface. Our method is independent of the optical absorption properties of the reaction products and/or the catalysts.
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34. 34
  Cialla, D.; Pollok, S.; Steinbrücker, C.; Weber, K.; Popp, J. SERS-Based Detection of Biomolecules Nanophotonics 2014, 3, 383– 411 DOI: 10.1515/nanoph-2013-0024
  34
  SERS-based detection of biomolecules
  Cialla, Dana; Pollok, Sibyll; Steinbruecker, Carolin; Weber, Karina; Popp, Juergen; Perelman, Lev T.
  Nanophotonics (2014), 3 (6), 383-411CODEN: NANOLP; ISSN:2192-8614. (Walter de Gruyter GmbH)
  A review. In order to detect biomols., different approaches using for instance biol., spectroscopic or imaging techniques were established. Due to the broad variety of these methods, this review is focused on surface enhanced Raman spectroscopy (SERS) as an anal. tool in biomol. detection. Here, the mol. specificity of Raman spectroscopy is combined with metallic nanoparticles as sensor platform, which enhances the signal intensity by several orders of magnitude. Within this article, the characterization of diverse biomols. by SERS is explained and moreover current application fields are presented. The SERS intensity and as a consequence thereof the reliable detection of the biomol. of interest is affected by distance, orientation and affinity of the mol. towards the metal surface. Furthermore, the great capability of the SERS technique for cutting-edge applications like pathogen detection and cancer diagnosis is highlighted. The authors wish to motivate by this comprehensive and crit. summary researchers from various scientific background to create their own ideas and schemes for a SERS-based detection and anal. of biomols.
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35. 35
  Peng, F.; Su, Y. Y.; Zhong, Y. L.; Fan, C. H.; Lee, S. T.; He, Y. Silicon Nanomaterials Platform for Bioimaging, Biosensing, and Cancer Therapy Acc. Chem. Res. 2014, 47, 612– 623 DOI: 10.1021/ar400221g
  35
  Silicon Nanomaterials Platform for Bioimaging, Biosensing, and Cancer Therapy
  Peng, Fei; Su, Yuanyuan; Zhong, Yiling; Fan, Chunhai; Lee, Shuit-Tong; He, Yao
  Accounts of Chemical Research (2014), 47 (2), 612-623CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
  A review. Silicon nanomaterials are an important class of nanomaterials with great potential for technologies including energy, catalysis, and biotechnol., because of their many unique properties, including biocompatibility, abundance, and unique electronic, optical, and mech. properties, among others. Silicon nanomaterials are known to have little or no toxicity due to favorable biocompatibility of silicon, which is an important precondition for biol. and biomedical applications. In addn., huge surface-to-vol. ratios of silicon nanomaterials are responsible for their unique optical, mech., or electronic properties, which offer exciting opportunities for design of high-performance silicon-based functional nanoprobes, nanosensors, and nanoagents for biol. anal. and detection and disease treatment. Moreover, silicon is the second most abundant element (after oxygen) on earth, providing plentiful and inexpensive resources for large-scale and low-cost prepn. of silicon nanomaterials for practical applications. Because of these attractive traits, and in parallel with a growing interest in their design and synthesis, silicon nanomaterials are extensively investigated for wide-ranging applications, including energy, catalysis, optoelectronics, and biol. Among them, bioapplications of silicon nanomaterials are of particular interest. In the past decade, scientists have made an extensive effort to construct a silicon nanomaterials platform for various biol. and biomedical applications, such as biosensors, bioimaging, and cancer treatment, as new and powerful tools for disease diagnosis and therapy. Nonetheless, there are few review articles covering these important and promising achievements to promote the awareness of development of silicon nanobiotechnol. In this Account, we summarize recent representative works to highlight the recent developments of silicon functional nanomaterials for a new, powerful platform for biol. and biomedical applications, including biosensor, bioimaging, and cancer therapy. First, we show that the interesting photoluminescence properties (e.g., strong fluorescence and robust photostability) and excellent biocompatibility of silicon nanoparticles (SiNPs) are superbly suitable for direct and long-term visualization of biol. systems. The strongly fluorescent SiNPs are highly effective for bioimaging applications, esp. for long-term cellular labeling, cancer cell detection, and tumor imaging in vitro and in vivo with high sensitivity. Next, we discuss the utilization of silicon nanomaterials to construct high-performance biosensors, such as silicon-based field-effect transistors (FET) and surface-enhanced Raman scattering (SERS) sensors, which hold great promise for ultrasensitive and selective detection of biol. species (e.g., DNA and protein). Then, we introduce recent exciting research findings on the applications of silicon nanomaterials for cancer therapy with encouraging therapeutic outcomes. Lastly, we highlight the major challenges and promises in this field, and the prospect of a new nanobiotechnol. platform based on silicon nanomaterials.
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36. 36
  Pettinger, B. Single-Molecule Surface- and Tip-Enhanced Raman Spectroscopy Mol. Phys. 2010, 108, 2039– 2059 DOI: 10.1080/00268976.2010.506891
  There is no corresponding record for this reference.
37. 37
  Dieringer, J. A.; Mcfarland, A. D.; Shah, N. C.; Stuart, D. A.; Whitney, A. V.; Yonzon, C. R.; Young, M. A.; Zhang, X.; Van Duyne, R. P. Surface Enhanced Raman Spectroscopy: New Materials, Concepts, Characterization Tools, and Applications Faraday Discuss. 2006, 132, 9– 26 DOI: 10.1039/B513431P
  37
  Surface enhanced Raman spectroscopy: new materials, concepts, characterization tools, and applications
  Dieringer, Jon A.; McFarland, Adam D.; Shah, Nilam C.; Stuart, Douglas A.; Whitney, Alyson V.; Yonzon, Chanda R.; Young, Matthew A.; Zhang, Xiaoyu; Van Duyne, Richard P.
  Faraday Discussions (2006), 132 (Surface Enhanced Raman Spectroscopy), 9-26CODEN: FDISE6; ISSN:1359-6640. (Royal Society of Chemistry)
  Surface-enhanced Raman spectroscopy (SERS) is currently experiencing a renaissance in its development driven by the remarkable discovery of single mol. SERS (SMSERS) and the explosion of interest in nanophotonics and plasmonics. Because excitation of the localized surface plasmon resonance (LSPR) of a nanostructured surface or nanoparticle lies at the heart of SERS, it is important to control all of the factors influencing the LSPR to maximize signal strength and ensure reproducibility. These factors include material, size, shape, interparticle spacing, and dielec. environment. All of these factors must be carefully controlled to ensure that the incident laser light maximally excites the LSPR in a reproducible manner. This article describes the use of nanosphere lithog. for the fabrication of highly reproducible and robust SERS substrates for both fundamental studies and applications. At. layer deposition (ALD) is introduced as a novel fabrication method for dielec. spacers to study the SERS distance dependence and control the nanoscale dielec. environment. Wavelength scanned SER excitation spectroscopy (WS SERES) measurements show that enhancement factors ∼108 are obtainable from NSL-fabricated surfaces and provide new insight into the electromagnetic-field enhancement mechanism. Tip-enhanced Raman spectroscopy (TERS) is an extremely promising new development to improve the generality and information content of SERS. A 2-dimensional correlation anal. is applied to SMSERS data. Finally, the 1st in vivo SERS glucose sensing study is presented.
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38. 38
  Moskovits, M. Persistent Misconceptions Regarding SERS Phys. Chem. Chem. Phys. 2013, 15, 5301– 5311 DOI: 10.1039/c2cp44030j
  38
  Persistent misconceptions regarding SERS
  Moskovits, Martin
  Physical Chemistry Chemical Physics (2013), 15 (15), 5301-5311CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  SERS is some 35 years old, and the subject of over 11 000 articles. The field of Plasmonics, and large aspects of Metamaterials are clearly based on concepts that became current as a result of SERS. Despite this, a no. of persistent, fuzzy ideas about the origin of the enhancement in SERS continue to be current even among SERS researchers, leading to the external impression that SERS is uniquely poorly understood. Six such ideas are discussed.
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39. 39
  Etchegoin, P. G.; Le Ru, E. C. Basic Electromagnetic Theory of SERS. In Surface Enhanced Raman Spectroscopy: Analytical, Biophysical and Life Science Applications; Schlücker, S., Ed.; Wiley-VCH: Weinheim, 2010; pp 1– 37.
  There is no corresponding record for this reference.
40. 40
  Etchegoin, P. G.; Le Ru, E. C. A Perspective on Single Molecule SERS: Current Status and Future Challenges Phys. Chem. Chem. Phys. 2008, 10, 6079– 6089 DOI: 10.1039/b809196j
  40
  A perspective on single molecule SERS: current status and future challenges
  Etchegoin, P. G.; Le Ru, E. C.
  Physical Chemistry Chemical Physics (2008), 10 (40), 6079-6089CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  A review in presented of a some of the basic principles underlying current research in single-mol. surface-enhanced Raman scattering (SM-SERS). The authors summarize, by the same token, conditions and characteristics that are common to most SM-SERS conditions, and discuss their implications for the understanding of data and for the comparison among different methods. The authors try to emphasize aspects of the problem that are not conventionally discussed in detail in the literature. In particular, the authors provide a full length discussion on the topics of: (i) the min. SERS enhancement necessary to observe a single mol., and (ii) the spatial distribution of the enhancement factor (EF) around hot-spots (which affects the statistics of SM-SERS events). A brief outlook into future perspectives of the different techniques used in SM-SERS and a few outstanding questions are also provided.
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41. 41
  Shanthil, M.; Thomas, R.; Swathi, R. S.; Thomas, K. G. Ag@SiO₂ Core–Shell Nanostructures: Distance-Dependent Plasmon Coupling and SERS Investigation J. Phys. Chem. Lett. 2012, 3, 1459– 1464 DOI: 10.1021/jz3004014
  41
  Ag@SiO2 Core-Shell Nanostructures: Distance-Dependent Plasmon Coupling and SERS Investigation
  Shanthil, M.; Thomas, Reshmi; Swathi, R. S.; Thomas, K. George
  Journal of Physical Chemistry Letters (2012), 3 (11), 1459-1464CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
  Enhancement of Raman signals of pyrene due to the enhanced elec. fields on the surface of silver nanoparticles has been investigated by controlling the thickness of the silica shell. Dimeric nanostructures having well-defined gaps between two silver nanoparticles were prepd., and the gap size (d) was varied from 1.5 to 40 nm. The mols. trapped at the dimeric junctions showed higher Raman signal enhancements when the gap was less than 15 nm due to the presence of amplified elec. field, in agreement with our theor. studies. The exptl. Raman enhancement factors at the hot spots follow a 1/dn dependence, with n = 1.5, in agreement with the recent theor. studies by Schatz and co-workers. Exptl. results presented here on the distance dependence of surface enhanced Raman spectroscopy (SERS) enhancement at the hot spots can provide insight on the design of newer plasmonic nanostructures with optimal nanogaps.
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42. 42
  Stewart, M. E.; Anderton, C. R.; Thompson, L. B.; Maria, J.; Gray, S. K.; Rogers, J. A.; Nuzzo, R. G. Nanostructured Plasmonic Sensors Chem. Rev. 2008, 108, 494– 521 DOI: 10.1021/cr068126n
  42
  Nanostructured plasmonic sensors
  Stewart, Matthew E.; Anderton, Christopher R.; Thompson, Lucas B.; Maria, Joana; Gray, Stephen K.; Rogers, John A.; Nuzzo, Ralph G.
  Chemical Reviews (Washington, DC, United States) (2008), 108 (2), 494-521CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
  A review. Theor. considerations on optical properties of metal nanoparticles and nanoholes, synthesis and fabrication of plasmonic nanostructures, and applications of plasmonic nanostructures in sensing and chem. imaging are discussed.
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43. 43
  Fan, M.; Andrade, G. F. S.; Brolo, A. G. A Review on the Fabrication of Substrates for Surface Enhanced Raman Spectroscopy and Their Applications in Analytical Chemistry Anal. Chim. Acta 2011, 693, 7– 25 DOI: 10.1016/j.aca.2011.03.002
  43
  A review on the fabrication of substrates for surface enhanced Raman spectroscopy and their applications in analytical chemistry
  Fan, Meikun; Andrade, Gustavo F. S.; Brolo, Alexandre G.
  Analytica Chimica Acta (2011), 693 (1-2), 7-25CODEN: ACACAM; ISSN:0003-2670. (Elsevier B.V.)
  A review. This work reviews different types of substrates used for surface-enhanced Raman scattering (SERS) that were developed in the last 10 years. The different techniques of self-assembly to immobilize metallic nanoparticles on solid support are covered. An overview of SERS platforms developed using nanolithog. methods, including electron-beam (e-beam) lithog. and focused ion beam (FIB) milling are also included, together with several examples of template-based methodologies to generate metallic nano-patterns. The potential of SERS to impact several aspects of anal. chem. is demonstrated by selected examples of applications in electrochem., biosensing, environmental anal., and remote sensing. This review shows that highly enhancing SERS substrates with a high degree of reliability and reproducibility can now be fabricated at relative low cost, indicating that SERS may finally realize its full potential as a very sensitive tool for routine anal. applications.
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44. 44
  The magnitude of the SERS enhancement is often described by the term “enhancement factor” (EF). It is a theoretical number that can be calculated with multiple methods. Each gives certain advantages over the others. Two examples of the methods to calculate EFs are the substrate EF (EF) and the analytical AEF (AEF), which are calculated as
  $EF = \frac{I_{SERS} / N_{Sur}}{I_{RS} / N_{Vol}}$
  where I_SERS is the intensity of the signal under SERS conditions, N_sur the amount of molecules adsorbed on the substrates surface in the spot size of the incident laser, I_RS the average intensity of the signal during normal Raman spectroscopy, and N_vol the average number of molecules in the volume probed by normal Raman spectroscopy.
  $AEF = \frac{I_{SERS} / c_{SERS}}{I_{RS} / c_{RS}}$
  where c_SERS is the concentration of analyte under SERS conditions. For details, we refer to the pioneering work of Felidj and co-workers:
  Felidj, N.; Aubard, J.; Levi, G.; Krenn, J. R.; Salerno, M.; Schider, G.; Lamprecht, P.; Leitner, A.; Aussenegg, F. R. Controlling the Optical Response of Regular Arrays of Gold Particles for Surface-Enhanced Raman Scattering Phys. Rev. B: Condens. Matter Mater. Phys. 2002, 65, 075419 DOI: 10.1103/PhysRevB.65.075419
  There is no corresponding record for this reference.
45. 45
  Ngoc, L. L. T.; Jin, M.; Wiedemair, J.; van den Berg, A.; Carlen, E. T. Large Area Metal Nanowire Arrays with Tunable Sub-20 Nm Nanogaps ACS Nano 2013, 7, 5223– 5234 DOI: 10.1021/nn4009559
  There is no corresponding record for this reference.
46. 46
  Jin, M.; Pully, V.; Otto, C.; van den Berg, A.; Carlen, E. T. High-Density Periodic Arrays of Self-Aligned Subwavelength Nanopyramids for Surface-Enhanced Raman Spectroscopy J. Phys. Chem. C 2010, 114, 21953– 21959 DOI: 10.1021/jp106245a
  46
  High-Density Periodic Arrays of Self-Aligned Subwavelength Nanopyramids for Surface-Enhanced Raman Spectroscopy
  Jin, Mingliang; Pully, Vishnu; Otto, Cees; van den Berg, Albert; Carlen, Edwin T.
  Journal of Physical Chemistry C (2010), 114 (50), 21953-21959CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
  Novel nanotextured surfaces are presented with periodically self-aligned subwavelength nanogroove and nanopyramid structures with precisely defined pitch λg that are closely packed with 2 nm sepn. gaps over large areas and form high-d. arrays of hot-spot scattering sites ideally suited for surface-enhanced Raman scattering (SERS) and Raman spectroscopy. The simple self-aligning fabrication technique requires only a single lithog. step and wet anisotropic etching. Measured av. Raman enhancement factors of G ≈ 106 from rhodamine 6G (R6G) on patterned Au surfaces with λg = 200 nm are consistent with numerical calcns. The nanostructured surfaces can be scaled to smaller dimensions, which results in increased enhancement as well as increased hot-spot spatial d.
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47. 47
  Wu, D.-Y.; Li, J.-F.; Ren, B.; Tian, Z.-Q. Electrochemical Surface-Enhanced Raman Spectroscopy of Nanostructures Chem. Soc. Rev. 2008, 37, 1025– 1041 DOI: 10.1039/b707872m
  47
  Electrochemical surface-enhanced Raman spectroscopy of nanostructures
  Wu, De-Yin; Li, Jian-Feng; Ren, Bin; Tian, Zhong-Qun
  Chemical Society Reviews (2008), 37 (5), 1025-1041CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
  A review. This tutorial review 1st describes the early history of SERS as the 1st SERS spectra were obtained from an electrochem. cell, which led to the discovery of the SERS effect in mid-1970s. Up to date, over 500 papers were published on various aspects of SERS from electrochem. systems. The authors then highlight important features of electrochem. SERS (EC-SERS). There are 2 distinctively different properties of elec. fields, the electromagnetic field and static electrochem. field, coexisting in electrochem. systems with various nanostructures. Both chem. and phys. enhancements can be influenced to some extent by applying an electrode potential, which makes EC-SERS one of the most complicated systems in SERS. Great efforts were made to comprehensively understand SERS and analyze EC-SERS spectra from the chem. and phys. enhancement mechanisms to provide meaningful information for revealing the mechanisms of electrochem. adsorption and reaction. The EC-SERS expts. and applications are then discussed from prepn. of nanostructured electrodes to study of SERS mechanisms and from characterization of adsorption configuration to elucidation of electrochem. reaction mechanisms. Finally, prospective developments of EC-SERS in substrates, methods and theory are discussed.
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48. 48
  Yuan, T.; Ngoc, L. L. T.; van Nieuwkasteele, J.; Odijk, M.; van den Berg, A.; Permentier, H.; Bischoff, R.; Carlen, E. T. In Situ Surface-Enhanced Raman Spectroelectrochemical Analysis System with a Hemin Modified Nanostructured Gold Surface Anal. Chem. 2015, 87, 2588– 2592 DOI: 10.1021/ac504136j
  48
  In Situ Surface-Enhanced Raman Spectroelectrochemical Analysis System with a Hemin Modified Nanostructured Gold Surface
  Yuan, Tao; Le Thi Ngoc, Loan; van Nieuwkasteele, Jan; Odijk, Mathieu; van den Berg, Albert; Permentier, Hjalmar; Bischoff, Rainer; Carlen, Edwin T.
  Analytical Chemistry (Washington, DC, United States) (2015), 87 (5), 2588-2592CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
  An integrated surface-enhanced Raman scattering (SERS) spectroelectrochem. (SEC) anal. system is presented that combines a small vol. microfluidic sample chamber (<100 μL) with a compact three-electrode configuration for in situ surface-enhanced Raman spectroelectrochem. The SEC system includes a nanostructured Au surface that serves dual roles as the electrochem. working electrode (WE) and SERS substrate, a microfabricated Pt counter electrode (CE), and an external Ag/AgCl ref. electrode (RE). The nanostructured Au WE enables highly sensitive in situ SERS spectroscopy through large and reproducible SERS enhancements, which eliminates the need for resonant wavelength matching of the laser excitation source with the electronic absorption of the target mol. The new SEC anal. system has the merits of wide applicability to target mols., small sample vol., and a low detection limit. We demonstrate in situ SERS spectroelectrochem. measurements of the metalloporphyrin hemin showing shifts of the iron oxidn. marker band ν4 with the nanostructured Au working electrode under precise potential control.
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49. 49
  McBreen, P. H.; Moskovits, M. A Surface-Enhanced Interacting Raman Study of Ethylene and Oxygen with Supported Silver Catalysts J. Catal. 1987, 103, 188– 199 DOI: 10.1016/0021-9517(87)90105-9
  There is no corresponding record for this reference.
50. 50
  Boghosian, S.; Bebelis, S.; Vayenas, C. G.; Papatheodorou, G. N. In Situ High Temperature SERS Study of Ag Catalysts Electrodes during Ethylene Epoxidation J. Catal. 1989, 117, 561– 565 DOI: 10.1016/0021-9517(89)90366-7
  There is no corresponding record for this reference.
51. 51
  Mikami, Y.; Dhakshinamoorthy, A.; Alvaro, M.; García, H. Catalytic Activity of Unsupported Gold Nanoparticles Catal. Sci. Technol. 2013, 3, 58– 69 DOI: 10.1039/C2CY20068F
  51
  Catalytic activity of unsupported gold nanoparticles
  Mikami, Yusuke; Dhakshinamoorthy, Amarajothi; Alvaro, Mercedes; Garcia, Hermenegildo
  Catalysis Science & Technology (2013), 3 (1), 58-69CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
  A review. This article reviews some of the compelling evidence showing that colloidal gold nanoparticles without any solid support exhibit intrinsic catalytic activity for some of the typical gold-catalyzed reactions including CO oxidn., aerobic oxidn. of alcs. and diols, borohydride redns., and carbon-carbon cross coupling reaction among other reactions. A crit. view of the state-of-the-art indicating open issues such as the role of the nature and concn. of the ligand and the possibility of prepg. colloidal samples with preferential crystallog. planes is provided.
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52. 52
  Christopher, P.; Xin, H.; Linic, S. Visible-Light-Enhanced Catalytic Oxidation Reactions on Plasmonic Silver Nanostructures Nat. Chem. 2011, 3, 467– 472 DOI: 10.1038/nchem.1032
  52
  Visible-light-enhanced catalytic oxidation reactions on plasmonic silver nanostructures
  Christopher, Phillip; Xin, Hongliang; Linic, Suljo
  Nature Chemistry (2011), 3 (6), 467-472CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)
  Catalysis plays a crit. role in chem. conversion, energy prodn. and pollution mitigation. High activation barriers assocd. with rate-limiting elementary steps require most com. heterogeneous catalytic reactions to be run at relatively high temps., which compromises energy efficiency and the long-term stability of the catalyst. Here we show that plasmonic nanostructures of silver can concurrently use low-intensity visible light (on the order of solar intensity) and thermal energy to drive catalytic oxidn. reactions-such as ethylene epoxidn., CO oxidn., and NH3 oxidn.-at lower temps. than their conventional counterparts that use only thermal stimulus. Based on kinetic isotope expts. and d. functional calcns., we postulate that excited plasmons on the silver surface act to populate O2 antibonding orbitals and so form a transient neg.-ion state, which thereby facilitates the rate-limiting O2-dissocn. reaction. The results could assist the design of catalytic processes that are more energy efficient and robust than current processes.
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53. 53
  Dorain, P. B.; Von Raben, K. U.; Chang, R. K.; Laube, B. L. Catalytic Formation of SO₃^2- and SO₄^2- from SO₂ on Silver Observed by Surface-Enhanced Raman Scattering Chem. Phys. Lett. 1981, 84, 405– 409 DOI: 10.1016/0009-2614(81)80373-9
  There is no corresponding record for this reference.
54. 54
  Zhang, Z.; Deckert-Gaudig, T.; Deckert, V. Label-Free Monitoring of Plasmonic Catalysis at the Nanoscale Analyst 2015, 140, 4325– 4335 DOI: 10.1039/C5AN00630A
  There is no corresponding record for this reference.
55. 55
  Bethke, K. A.; Kung, H. H. Supported Ag Catalysts for the Lean Reduction of NO with C₃H₆ J. Catal. 1997, 172, 93– 102 DOI: 10.1006/jcat.1997.1794
  55
  Supported Ag catalysts for the lean reduction of NO with C3H6
  Bethke, K. A.; Kung, H. H.
  Journal of Catalysis (1997), 172 (1), 93-102CODEN: JCTLA5; ISSN:0021-9517. (Academic Press)
  The activities of 2 and 6 wt% Ag/Al2O3 catalysts for lean NO redn. with C3H6 were compared. High conversions of NO to N2 were obtained over 2 wt% Ag/Al2O3. In contrast, the NO conversions to N2 were much lower over 6 wt% Ag/Al2O3, and this catalyst formed a substantial amt. of N2O. The difference in the behavior of the two catalysts was attributed to the much higher Ag dispersion for the 2 wt% than the 6 wt% sample, such that the oxidn. states of Ag were different under reaction conditions. The 2 wt% Ag/Al2O3 was believed to contain silver in the +1 oxidn. state under reaction conditions, while the 6 wt% Ag/Al2O3 catalyst contained Ag0 particles, the amt. of which decreased at higher temps. The presence of Ag0 resulted in a high rate of C3H6 combustion at the expense of NOx redn. A synergistic effect was obsd. over a mixt. of Al2O3 and 2 or 6 wt% Ag/Al2O3 and was attributed to the transfer of a very short-lived intermediate from Al2O3 to Ag/Al2O3 or vice versa.
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56. 56
  Marimuthu, A.; Zhang, J.; Linic, S. Tuning Selectivity in Propylene Epoxidation by Plasmon Mediated Photo-Switching of Cu Oxidation State Science 2013, 339, 1590– 1593 DOI: 10.1126/science.1231631
  56
  Tuning Selectivity in Propylene Epoxidation by Plasmon Mediated Photo-Switching of Cu Oxidation State
  Marimuthu, Andiappan; Zhang, Jianwen; Linic, Suljo
  Science (Washington, DC, United States) (2013), 339 (6127), 1590-1593CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
  Oxidn. of functioning copper has restricted its applicability as a catalyst for com. important epoxidn. of propylene to form propylene oxide. Here, we report that steady-state selectivity in propylene epoxidn. on copper (Cu) nanoparticles increases sharply when the catalyst is illuminated with visible light. The selectivity increase is accompanied by light-induced redn. of the surface Cu atoms, which is brought about by photoexcitation of the localized surface plasmon resonance (LSPR) of Cu. We discuss multiple mechanisms by which Cu LSPR weakens the Cu-O bonds, reducing Cu2O.
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57. 57
  Karelovic, A.; Ruiz, P. The Role of Copper Particle Size in Low Pressure Methanol Synthesis via CO₂ Hydrogenation over Cu/ZnO Catalysts Catal. Sci. Technol. 2015, 5, 869– 881 DOI: 10.1039/C4CY00848K
  57
  The role of copper particle size in low pressure methanol synthesis via CO2 hydrogenation over Cu/ZnO catalysts
  Karelovic, Alejandro; Ruiz, Patricio
  Catalysis Science & Technology (2015), 5 (2), 869-881CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
  Cu/ZnO catalysts with different mean Cu particle sizes were prepd. by wet impregnation of copper nitrate onto a zinc oxide support. Their performance was studied in methanol synthesis reaction from CO2 and H2 at temps. between 160 and 225 °C and a pressure of 7 bar. Selective methanol formation is favored at lower temps. due to the suppression of CO prodn. Activation energies were 8-11 kcal mol-1 for methanol formation and 29-31 kcal mol-1 for CO formation and were similar for all the catalysts. For catalysts with copper cluster sizes between 8.5 and 37.3 nm, the methanol formation rates normalized by surface copper atoms were independent of copper particle size. On the contrary, CO formation rates are enhanced over catalysts with smaller copper clusters. Higher selectivity to methanol is favored over catalysts possessing larger copper nanoparticles. Catalysts with copper loading ≥8 wt.% showed a strong sintering of copper nanoparticles and also a significant growth of ZnO support crystallites. These catalysts presented higher intrinsic rates for methanol formation (4 × 10-3 s-1 at 180 °C) compared to catalysts with lower copper loading (0.9 × 10-3 s-1). As the kinetic parameters were similar for all Cu/ZnO catalysts, it is proposed that catalysts with large copper and ZnO particles form new active sites that led ultimately to a very high methanol synthesis activity and selectivity. It is suggested that the important sintering of Cu particles modifies the structure of copper promoting the hydrogenation rate in methanol synthesis.
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58. 58
  Wang, J. L.; Ando, R. A.; Camargo, P. H. C. Investigating the Plasmon-Mediated Catalytic Activity of AgAu Nanoparticles as a Function of Composition: Are Two Metals Better than One? ACS Catal. 2014, 4, 3815– 3819 DOI: 10.1021/cs501189m
  58
  Investigating the Plasmon-Mediated Catalytic Activity of AgAu Nanoparticles as a Function of Composition: Are Two Metals Better than One?
  Wang, J. L.; Ando, Romulo A.; Camargo, Pedro H. C.
  ACS Catalysis (2014), 4 (11), 3815-3819CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  The surface plasmon resonance (SPR) excitation by visible light in plasmonic nanostructures can be put to work to mediate catalytic processes. However, the role of compn. in bimetallic nanoparticles over the SPR-mediated catalytic activity remains unclear. The authors studied herein the SPR-mediated catalytic activity of AgAu nanoparticles as a function of compn. toward the oxidn. of p-aminothiophenol to p,p'-dimercaptoazobenzene. A volcano-type relation between compn. and product conversion was obsd., with a max. activity obsd. for Ag0.19Au0.81 nanoparticles. The variations in catalytic activity could be explained by the balance between the matching of the excitation wavelength with SPR position and the plasmonic damping due to interband transitions >500 nm. Probably the precise control over compn. allows the fine-tuning of catalytic activity in SPR-mediated catalytic processes.
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59. 59
  He, R.; Wang, Y.; Wang, X.; Wang, Z.; Liu, G.; Zhou, W.; Wen, L.; Li, Q.; Wang, X.; Chen, X.; Zeng, J.; Hou, J. G. Facile Synthesis of Pentacle Gold-Copper Alloy Nanocrystals and Their Plasmonic and Catalytic Properties Nat. Commun. 2014, 5, 4327 DOI: 10.1038/ncomms5327
  59
  Facile synthesis of pentacle gold-copper alloy nanocrystals and their plasmonic and catalytic properties
  He, Rong; Wang, You-Cheng; Wang, Xiaoyong; Wang, Zhantong; Liu, Gang; Zhou, Wei; Wen, Longping; Li, Qunxiang; Wang, Xiaoping; Chen, Xiaoyuan; Zeng, Jie; Hou, J. G.
  Nature Communications (2014), 5 (), 4327CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
  The combination of gold and copper is a good way to pull down the cost of gold and ameliorate the instability of copper. Through shape control, the synergy of these two metals can be better exploited. Here, we report an aq. phase route to the synthesis of pentacle gold-copper alloy nanocrystals with fivefold twinning, the size of which can be tuned in the range from 45 to 200 nm. The growth is found to start from a decahedral core, followed by protrusion of branches along twinning planes. Pentacle products display strong localized surface plasmon resonance peaks in the near-IR region. Under irradn. by an 808-nm laser, 70-nm pentacle nanocrystals exhibit a notable photothermal effect to kill 4T1 murine breast tumors established on BALB/c mice. In addn., 70-nm pentacle nanocrystals show better catalytic activity than conventional citrate-coated 5-nm Au nanoparticles towards the redn. of p-nitrophenol to p-aminophenol by sodium borohydride.
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60. 60
  Santos Costa, J. C.; Corio, P.; Marcia Rossi, L. Catalytic Oxidation of Cinnamyl Alcohol Using Au – Ag Nanotubes Investigated by Surface-Enhanced Raman Spectroscopy Nanoscale 2015, 7, 8536– 8543 DOI: 10.1039/C5NR01064K
  There is no corresponding record for this reference.
61. 61
  Kiyonaga, T.; Jin, Q.; Kobayashi, H.; Tada, H. Size-Dependence of Catalytic Activity of Gold Nanoparticles Loaded on Titanium (IV) Dioxide for Hydrogen Peroxide Decomposition ChemPhysChem 2009, 10, 2935– 2938 DOI: 10.1002/cphc.200900596
  61
  Size-Dependence of Catalytic Activity of Gold Nanoparticles Loaded on Titanium (IV) Dioxide for Hydrogen Peroxide Decomposition
  Kiyonaga, Tomokazu; Jin, Qiliang; Kobayashi, Hisayoshi; Tada, Hiroaki
  ChemPhysChem (2009), 10 (17), 2935-2938CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Size-dependence of catalytic activity of gold nanoparticles loaded on titanium (IV) dioxide for hydrogen peroxide decompn. is discussed.
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62. 62
  Laoufi, I.; Saint-Lager, M. C.; Lazzari, R.; Jupille, J.; Robach, O.; Garaudée, S.; Cabailh, G.; Dolle, P.; Cruguel, H.; Bailly, A. Size and Catalytic Activity of Supported Gold Nanoparticles: An in Operando Study during CO Oxidation J. Phys. Chem. C 2011, 115, 4673– 4679 DOI: 10.1021/jp1110554
  62
  Size and Catalytic Activity of Supported Gold Nanoparticles: An in Operando Study during CO Oxidation
  Laoufi, I.; Saint-Lager, M.-C.; Lazzari, R.; Jupille, J.; Robach, O.; Garaudee, S.; Cabailh, G.; Dolle, P.; Cruguel, H.; Bailly, A.
  Journal of Physical Chemistry C (2011), 115 (11), 4673-4679CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
  The origin of the catalytic activity of gold nanoparticles remains debated despite extensive studies. This in operando work investigates the relationship between catalytic activity and size/shape of gold nanoparticles supported on TiO2(110) during CO oxidn. The nanoparticles were synthesized by vapor deposition in ultrahigh vacuum. Their geometry was monitored in the presence of O2, Ar, or a mixt. of O2 + CO and of Ar + CO by grazing incidence small-angle X-ray scattering simultaneously with the catalytic activity. The occurrence of CO oxidn. induces a sintering directly correlated to the reaction rate. The catalytic activity is optimum for a nanoparticle's diam. of 2.1 ± 0.3 nm and a height of about six at. layers. Below this size, the activity drop corresponds to a height decrease. Rescaling of activities obtained in different exptl. conditions shows consistency of these results with published data using both "model" and "real" catalysts.
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63. 63
  Bell, S. E. J.; McCourt, M. R. SERS Enhancement by Aggregated Au Colloids: Effect of Particle Size Phys. Chem. Chem. Phys. 2009, 11, 7455– 7462 DOI: 10.1039/b906049a
  63
  SERS enhancement by aggregated Au colloids: effect of particle size
  Bell, Steven E. J.; McCourt, Maighread R.
  Physical Chemistry Chemical Physics (2009), 11 (34), 7455-7462CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  Aggregated Au colloids were widely used as SERS enhancing media for many years but to date there was no systematic study of the effect of the particle size on the enhancements given by simple aggregated Au colloid solns. Previous systematic studies on isolated particles in soln. or multiple particles deposited onto surfaces reported widely different optimum particle sizes for the same excitation wavelength and also disagreed on the extent to which surface plasmon absorption spectra were a good predictor of enhancement factors. The spectroscopic properties of a range of samples of monodisperse Au colloids with diams. ranging from 21 to 146 nm were studied in soln. The UV/visible absorption spectra of the colloids show complex changes as a function of aggregating salt (MgSO4) concn. which diminish when the colloid is fully aggregated. Under these conditions, the relative SERS enhancements provided by the variously sized colloids vary very significantly across the size range. The largest signals in the raw data are obsd. for 46 nm colloids but correction for the total surface area available to generate enhancement shows that particles with 74 nm diam. give the largest enhancement per unit surface area. The obsd. enhancements do not correlate with absorbance at the excitation wavelength but the large differences between differently sized colloids demonstrate that even in the randomly aggregated particle assemblies studied here, inhomogeneous broadening does not mask the underlying changes due to differences in particle diam.
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64. 64
  Zhang, Q.; Blom, D. A.; Wang, H. Nanoporosity-Enhanced Catalysis on Subwavelength Au Nanoparticles: A Plasmon-Enhanced Spectroscopic Study Chem. Mater. 2014, 26, 5131– 5142 DOI: 10.1021/cm502508d
  64
  Nanoporosity-Enhanced Catalysis on Subwavelength Au Nanoparticles: a Plasmon-Enhanced Spectroscopic Study
  Zhang, Qingfeng; Blom, Douglas A.; Wang, Hui
  Chemistry of Materials (2014), 26 (17), 5131-5142CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
  The authors show that subwavelength Au nanoparticles with nanoscale surface porosity represent a unique bifunctional nanostructure that serves as both high-performance SERS substrates and efficient surface catalysts, allowing one to unravel the kinetics and pathways of surface-catalyzed reactions with unprecedented sensitivity and detail through time-resolved plasmon-enhanced spectroscopic measurements. The origin of the nanoporosity-enhanced catalytic activity can be interpreted as a consequence of high abundance of undercoordinated surface atoms at the steps and kinks on the highly curved surfaces of Au porous nanoparticles. By measuring SERS signals from the monolayer mols. preadsorbed on the surfaces of Au porous nanoparticles, the authors gained quant. insights into the intrinsic kinetics and mechanisms of Au-catalyzed hydrogenation of arom. nitro compds. with minimal complication introduced by the mol. diffusion, adsorption, and desorption.
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65. 65
  Zhang, Q.; Wang, H. Facet-Dependent Catalytic Activities of Au Nanoparticles Enclosed by High-Index Facets ACS Catal. 2014, 4, 4027– 4033 DOI: 10.1021/cs501445h
  65
  Facet-Dependent Catalytic Activities of Au Nanoparticles Enclosed by High-Index Facets
  Zhang, Qingfeng; Wang, Hui
  ACS Catalysis (2014), 4 (11), 4027-4033CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  We employed surface-enhanced Raman scattering as a noninvasive in situ spectroscopic tool to quant. study the intrinsic facet-dependent catalytic activities of colloidal subwavelength Au nanoparticles enclosed by various types of well-defined high-index facets using the catalytic hydrogenation of 4-nitrothiophenol as a model reaction. Our results provide compelling exptl. evidence on the crucial roles of undercoordinated surface atoms in Au-based heterogeneous catalysis and shed light on the underlying relationship between the at.-level surface structures and the intrinsic catalytic activities of Au nanocatalysts.
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66. 66
  Cui, Q.; Yashchenok, A.; Zhang, L.; Li, L.; Masic, A.; Wienskol, G.; Möhwald, H.; Bargheer, M. Fabrication of Bifunctional Gold/gelatin Hybrid Nanocomposites and Their Application ACS Appl. Mater. Interfaces 2014, 6, 1999– 2002 DOI: 10.1021/am5000068
  66
  Fabrication of Bifunctional Gold/Gelatin Hybrid Nanocomposites and Their Application
  Cui, Qianling; Yashchenok, Alexey; Zhang, Lu; Li, Lidong; Masic, Admir; Wienskol, Gabriele; Mohwald, Helmuth; Bargheer, Matias
  ACS Applied Materials & Interfaces (2014), 6 (3), 1999-2002CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
  A facile method is presented to integrate large gold nanoflowers (∼80 nm) and small gold nanoparticles (2-4 nm) into a single entity, exhibiting both surface-enhanced Raman scattering (SERS) and catalytic activity. The as-prepd. gold nanoflowers were coated by a gelatin layer, in which the gold precursor was adsorbed and in situ reduced into small gold nanoparticles. The thickness of the gelatin shell is controlled to less than 10 nm, ensuring that the small gold nanoparticles are still in a SERS-active range of the inner Au core. Therefore, the reaction catalyzed by these nanocomposites can be monitored in situ using label-free SERS spectroscopy. In addn., these bifunctional nanocomposites are also attractive candidates for application in SERS monitoring of bioreactions because of their excellent biocompatibility.
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67. 67
  Xie, W.; Walkenfort, B.; Schlücker, S. Label-Free SERS Monitoring of Chemical Reactions Catalyzed by Small Gold Nanoparticles Using 3D Plasmonic Superstructures J. Am. Chem. Soc. 2013, 135, 1657– 1660 DOI: 10.1021/ja309074a
  67
  Label-Free SERS Monitoring of Chemical Reactions Catalyzed by Small Gold Nanoparticles Using 3D Plasmonic Superstructures
  Xie, Wei; Walkenfort, Bernd; Schluecker, Sebastian
  Journal of the American Chemical Society (2013), 135 (5), 1657-1660CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Label-free in situ surface-enhanced Raman scattering (SERS) monitoring of reactions catalyzed by small gold nanoparticles using rationally designed plasmonic superstructures is presented. Catalytic and SERS activities are integrated into a single bifunctional 3D superstructure comprising small gold satellites self-assembled onto a large shell-isolated gold core, which eliminates photocatalytic side reactions.
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68. 68
  van Schrojenstein Lantman, E. M. Raman Nanospectroscopy of a Photo-Catalytic Reaction. Ph.D. Thesis, Utrecht University, Utrecht, The Netherlands, 2014.
  There is no corresponding record for this reference.
69. 69
  Sun, M.; Xu, H. A Novel Application of Plasmonics: Plasmon-Driven Surface-Catalyzed Reactions Small 2012, 8, 2777– 2786 DOI: 10.1002/smll.201200572
  69
  A Novel Application of Plasmonics: Plasmon-Driven Surface-Catalyzed Reactions
  Sun, Mengtao; Xu, Hongxing
  Small (2012), 8 (18), 2777-2786CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A review. The first exptl. and theor. evidence of the surface-catalyzed reaction of p,p'-dimercaptoazobenzene (DMAB) produced from para-aminothiophenol (PATP) by local surface plasmons was reported in 2010, and since that time a series of investigations have supported these findings using different exptl. and theor. methods. Recent work has also found that local plasmons can drive a surface-catalyzed reaction of DMAB converted from 4-nitrobenzenethiol (4NBT), assisted by local surface plasmons. There are at least three important discoveries in these investigations: (1) in the field of surface-enhanced Raman scattering (SERS) the widely accepted misinterpretation (since 1994) that the chem. mechanism resulting in three addnl. Raman peaks of PATP in Ag or Au solns. has been cor. with a new mechanism; (2) it is confirmed that SERS is not always a noninvasive technique, and under certain conditions cannot always obtain the vibrational fingerprint information of the original surface species; (3) a novel method to synthesize new mols., induced by local surface plasmons or plasmon waveguides on the nanoscale, has been found. This Review considers recent novel applications of plasmonics to chem. reactions, esp. to plasmon-driven surface-catalyzed reactions.
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70. 70
  Harvey, C. E.; Weckhuysen, B. M. Surface- and Tip-Enhanced Raman Spectroscopy as Operando Probes for Monitoring and Understanding Heterogeneous Catalysis Catal. Lett. 2015, 145, 40– 57 DOI: 10.1007/s10562-014-1420-4
  70
  Surface- and Tip-Enhanced Raman Spectroscopy as Operando Probes for Monitoring and Understanding Heterogeneous Catalysis
  Harvey, Clare E.; Weckhuysen, Bert M.
  Catalysis Letters (2015), 145 (1), 40-57CODEN: CALEER; ISSN:1011-372X. (Springer)
  Abstr.: Surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS) were until recently limited in their applicability to the majority of heterogeneous catalytic reactions. Recent developments begin to resolve the conflicting exptl. requirements for SERS and TERS on the one hand, and heterogeneous catalysis on the other hand. This article discusses the development and use of SERS and TERS to study heterogeneous catalytic reactions, and the exciting possibilities that may now be within reach thanks to the latest tech. developments. This will be illustrated with showcase examples from photo- and electrocatalysis. Graphical Abstr.: [Figure not available: see fulltext.].
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71. 71
  Chen, X.-J.; Cabello, G.; Wu, D.-Y.; Tian, Z.-Q. Surface-Enhanced Raman Spectroscopy toward Application in Plasmonic Photocatalysis on Metal Nanostructures J. Photochem. Photobiol., C 2014, 21, 54– 80 DOI: 10.1016/j.jphotochemrev.2014.10.003
  71
  Surface-enhanced Raman spectroscopy toward application in plasmonic photocatalysis on metal nanostructures
  Chen, Xue-Jiao; Cabello, Gema; Wu, De-Yin; Tian, Zhong-Qun
  Journal of Photochemistry and Photobiology, C: Photochemistry Reviews (2014), 21 (), 54-80CODEN: JPPCAF; ISSN:1389-5567. (Elsevier B.V.)
  Among photothermal, photovoltaic and photochem. techniques, photochem. is superior in energy storage and transportation by converting photons into chem. fuels. Recently plasmonic photocatalysis, based on localized surface plasmon resonance (LSPR) generated from noble metal nanostructures, has attracted much attention. It promotes photochem. reaction efficiency by optimizing the solar spectrum absorption and the surface reaction kinetics. The deeper understanding is in urgent need for the development of novel plasmonic photocatalysts. Surface-enhanced Raman spectroscopy (SERS), which is also originated from the LSPR effect, provides an excellent opportunity to probe and monitor plasmonic photoreactions in situ and in real-time, with a very high surface sensitivity and energy resoln. Here, fundamentals of plasmonic photocatalysis and SERS are first presented based on their connections to the LSPR effect. Following by a validity anal., latest studies of SERS applied for the plasmon mediated photochem. reaction are reviewed, focusing on the reaction kinetics and mechanism exploration. Finally, limitations of the present study, as well as the future research directions, are briefly analyzed and discussed.
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72. 72
  Pashaee, F.; Hou, R.; Gobbo, P.; Workentin, M. S.; Lagugné-Labarthet, F. Tip-Enhanced Raman Spectroscopy of Self-Assembled Thiolated Monolayers on Flat Gold Nanoplates Using Gaussian-Transverse and Radially Polarized Excitations J. Phys. Chem. C 2013, 117, 15639– 15646 DOI: 10.1021/jp403157v
  72
  Tip-Enhanced Raman Spectroscopy of Self-Assembled Thiolated Monolayers on Flat Gold Nanoplates Using Gaussian-Transverse and Radially Polarized Excitations
  Pashaee, Farshid; Hou, Renjie; Gobbo, Pierangelo; Workentin, Mark S.; Lagugne-Labarthet, Francois
  Journal of Physical Chemistry C (2013), 117 (30), 15639-15646CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
  Tip-enhanced Raman spectroscopy (TERS) is a highly sensitive spectroscopic technique that combines the spatial resoln. of scanning near-field techniques with the chem. specificity of vibrational spectroscopy. TERS is based on the excitation of the localized surface plasmon resonance at the apex of an AFM metalized tip, producing a confined and enhanced electromagnetic field. Due to the inherent local nature of TERS and its confinement in the optical near-field of the object, TERS measurements can also be used to probe monolayers adsorbed onto surfaces providing better surface specificity in addn. to higher spatial resoln. The authors implement here gap-mode TERS using Au nanoplates functionalized with thiolated ref. mols. such as alkoxy substituted azobenzene thiol and 4-nitrothiophenol. The monolayer is probed with a Ag coated AFM tip to obtain the largest electromagnetic field enhancement from the surface plasmon localized between the Ag tip and the functionalized Au surface. The TERS spectra was measured of the self-assembled monolayer on Au using 532 nm excitation that is linearly (Gaussian-transverse TEM00) and radially polarized. The nature of the collected TERS spectra for the thiolated mols. (azobenzene thiol and nitrothiophenol) that appear to be dependent on the polarization of the excitation light at the tip/substrate interface is reported.
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73. 73
  Tabatabaei, M.; Sangar, A.; Kazemi-zanjani, N.; Torchio, P.; Merlen, A.; Lagugné-Labarthet, F. Optical Properties of Silver and Gold Tetrahedral Nanopyramid Arrays Prepared by Nanosphere Lithography J. Phys. Chem. C 2013, 117, 14778– 14786 DOI: 10.1021/jp405125c
  73
  Optical Properties of Silver and Gold Tetrahedral Nanopyramid Arrays Prepared by Nanosphere Lithography
  Tabatabaei, Mohammadali; Sangar, Alexandre; Kazemi-Zanjani, Nastaran; Torchio, Philippe; Merlen, Alexandre; Lagugne-Labarthet, Francois
  Journal of Physical Chemistry C (2013), 117 (28), 14778-14786CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
  Tetrahedral nanopyramids made of Ag and Au over ITO/glass surfaces are fabricated. The protocol is based on nanosphere lithog. (NSL) with the deposition of thicker metal layers. After removing the microspheres used in the NSL process, an array of metallic tetrahedral nanostructures of ∼350-400 nm height is formed. The reported procedure avoids the use of any stabilizing surfactant mols. that are generally necessary to segregate the individual particles onto surfaces. The authors focus here on the optical and the phys. properties of these plasmonic surfaces using near-field spectroscopy in conjunction with finite difference time domain (FDTD) modeling of the elec. field. Remarkably, FDTD shows that the localized surface plasmon resonance is confined in the plane formed by the edges of 2 facing pyramids that is parallel to the polarization of the impinging excitation laser. The variable gap between the edges of 2 adjacent pyramids shows a broader localized surface plasmon and a larger sp. surface as opposed to the usual nanotriangle array. Localized enhancement of the elec. field is exptl. studied by coating the plasmonic surface with a thin film of photosensitive azopolymer onto the surface of the nanopyramids. Upon irradn., the deformation of the surface topog. is visualized by at. force microscopy and suggests the potentiality of these 3D nanopyramids for near-field enhancement. This last feature is clearly confirmed by surface-enhanced Raman scattering measurement with 4-nitrothiophenol mols. deposited on the pyramid platforms. The potentiality of such 3D nanostructures in plasmonics and surface spectroscopy is thus clearly demonstrated.
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74. 74
  Liu, W.-L.; Lin, F.-C.; Yang, Y.-C.; Huang, C.-H.; Gwo, S.; Huang, M. H.; Huang, J.-S. The Influence of Shell Thickness of Au@TiO₂ Core-Shell Nanoparticles on the Plasmonic Enhancement Effect in Dye-Sensitized Solar Cells Nanoscale 2013, 5, 7953– 7962 DOI: 10.1039/c3nr02800c
  74
  The influence of shell thickness of Au@TiO2 core-shell nanoparticles on the plasmonic enhancement effect in dye-sensitized solar cells
  Liu, Wei-Liang; Lin, Fan-Cheng; Yang, Yu-Chen; Huang, Chen-Hsien; Gwo, Shangjr; Huang, Michael H.; Huang, Jer-Shing
  Nanoscale (2013), 5 (17), 7953-7962CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
  Plasmonic core-shell nanoparticles (PCSNPs) can function as nanoantennas and improve the efficiency of dye-sensitized solar cells (DSSCs). To achieve max. enhancement, the morphol. of PCSNPs needs to be optimized. Here we precisely control the morphol. of AuiO2 PCSNPs and systematically study its influence on the plasmonic enhancement effect. The enhancement mechanism was found to vary with the thickness of the TiO2 shell. PCSNPs with a thinner shell mainly enhance the current, whereas particles with a thicker shell improve the voltage. While pronounced plasmonic enhancement was found in the near IR regime, wavelength-independent enhancement in the visible range was obsd. and attributed to the plasmonic heating effect. Emission lifetime measurement confirms that N719 mols. neighboring nanoparticles with TiO2 shells exhibit a longer lifetime than those in contact with metal cores. Overall, PCSNPs with a 5 nm shell give the highest efficiency enhancement of 23%. Our work provides a new synthesis route for well-controlled AuiO2 core-shell nanoparticles and gains insight into the plasmonic enhancement in DSSCs.
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75. 75
  Zhang, Z.; Deckert-Gaudig, T.; Singh, P.; Deckert, V. Single Molecule Level Plasmonic Catalysis – a Dilution Study of p-Nitrothiophenol on Gold Dimers Chem. Commun. 2015, 51, 3069– 3072 DOI: 10.1039/C4CC09008J
  75
  Single molecule level plasmonic catalysis - a dilution study of p-nitrothiophenol on gold dimers
  Zhang, Zhenglong; Deckert-Gaudig, Tanja; Singh, Pushkar; Deckert, Volker
  Chemical Communications (Cambridge, United Kingdom) (2015), 51 (15), 3069-3072CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  Surface plasmons on isolated gold dimers can initiate intermol. reactions of adsorbed p-nitrothiophenol. At the single mol. level when dimerization is not possible an intramol. reaction can be obsd. Exptl. evidence indicates that plasmon-induced hot electrons provide the required activation energy.
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76. 76
  Wang, P.; Huang, B.; Dai, Y.; Whangbo, M.-H. Plasmonic Photocatalysts: Harvesting Visible Light with Noble Metal Nanoparticles Phys. Chem. Chem. Phys. 2012, 14, 9813– 9825 DOI: 10.1039/c2cp40823f
  76
  Plasmonic photocatalysts: harvesting visible light with noble metal nanoparticles
  Wang, Peng; Huang, Baibiao; Dai, Ying; Whangbo, Myung-Hwan
  Physical Chemistry Chemical Physics (2012), 14 (28), 9813-9825CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  A review. The efforts to produce photocatalysts operating efficiently under visible light have led to a no. of plasmonic photocatalysts, in which noble metal nanoparticles are deposited on the surface of polar semiconductor or dielecs. particles. In the metal-semiconductor composite photocatalysts, the noble metal nanoparticles act as a major component for harvesting visible light due to their surface plasmon resonance while the metal-semiconductor interface efficiently separates the photogenerated electrons and holes. In this article, we survey various plasmonic photocatalysts that have been prepd. and characterized in recent years.
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77. 77
  Rycenga, M.; Wang, Z.; Gordon, E.; Cobley, C. M.; Schwartz, A. G.; Lo, C. S.; Xia, Y. Probing the Photothermal Effect of Gold-Based Nanocages with Surface Enhanced Raman Scattering (SERS) Angew. Chem., Int. Ed. 2009, 48, 9924– 9927 DOI: 10.1002/anie.200904382
  There is no corresponding record for this reference.
78. 78
  Kang, T.; Hong, S.; Choi, Y.; Lee, L. P. The Effect of Thermal Gradients in SERS Spectroscopy Small 2010, 6, 2649– 2652 DOI: 10.1002/smll.201000996
  78
  The Effect of Thermal Gradients in SERS Spectroscopy
  Kang, Taewook; Hong, Soongweon; Choi, Yeonho; Lee, Luke P.
  Small (2010), 6 (23), 2649-2652CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
  This study demonstrated the importance of temp. gradients due to photothermal effects on nanoplasmonic antennae in surface enhanced Raman scattering (SERS) spectroscopic measurements. Using 5-carboxytetramethylrhodamine (TAMRA)-labeled DNA, crit. photothermal effect in SERS spectroscopic measurements was obsd. Numerical anal. and exptl. results revealed that the local concn. of the target mols. near a SERS probe was not the same as the bulk concn., and this made a significant difference in sensitivity of the probes. Since SERS results showed that DNA could be not only depleted, but also enriched in adjacent areas, both these regions may be controlled by changing the shape or array of probes, the power of the excitation source, the chamber height, and the substrate materials. Crit. understanding of photothermal effects and temp. gradients can be applied to maximize the amplification of SERS signals and the effective design of sensitive SERS probes by inducing target mols. to focus on enrichment sites for future label-free biochem., chem., and environmental monitoring.
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79. 79
  Zhao, L.-B.; Huang, Y.-F.; Liu, X.-M.; Anema, J. R.; Wu, D.-Y.; Ren, B.; Tian, Z.-Q. A DFT Study on Photoinduced Surface Catalytic Coupling Reactions on Nanostructured Silver: Selective Formation of Azobenzene Derivatives from Para-Substituted Nitrobenzene and Aniline Phys. Chem. Chem. Phys. 2012, 14, 12919– 12929 DOI: 10.1039/c2cp41502j
  79
  A DFT study on photoinduced surface catalytic coupling reactions on nanostructured silver: selective formation of azobenzene derivatives from para-substituted nitrobenzene and aniline
  Zhao, Liu-Bin; Huang, Yi-Fan; Liu, Xiu-Min; Anema, Jason R.; Wu, De-Yin; Ren, Bin; Tian, Zhong-Qun
  Physical Chemistry Chemical Physics (2012), 14 (37), 12919-12929CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  We propose that arom. nitro and amine compds. undergo photochem. reductive and oxidative coupling, resp., to specifically produce azobenzene derivs. which exhibit characteristic Raman signals related to the azo group. A photoinduced charge transfer model is presented to explain the transformations obsd. in para-substituted ArNO2 and ArNH2 on nanostructured silver due to the surface plasmon resonance effect. Theor. calcns. show that the initial reaction takes place through excitation of an electron from the filled level of silver to the LUMO of an adsorbed ArNO2 mol., and from the HOMO of an adsorbed ArNH2 mol. to the unoccupied level of silver, during irradn. with visible light. The para-substituted ArNO2-· and ArNH2+· surface species react further to produce the azobenzene derivs. Our results may provide a new strategy for the syntheses of arom. azo dyes from arom. nitro and amine compds. based on the use of nanostructured silver as a catalyst.
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80. 80
  Pelaez, M.; Nolan, N. T.; Pillai, S. C.; Seery, M. K.; Falaras, P.; Kontos, A. G.; Dunlop, P. S. M.; Hamilton, J. W. J.; Byrne, J. A.; Shea, K. O. A Review on the Visible Light Active Titanium Dioxide Photocatalysts for Environmental Applications Appl. Catal., B 2012, 125, 331– 349 DOI: 10.1016/j.apcatb.2012.05.036
  80
  A review on the visible light active titanium dioxide photocatalysts for environmental applications
  Pelaez, Miguel; Nolan, Nicholas T.; Pillai, Suresh C.; Seery, Michael K.; Falaras, Polycarpos; Kontos, Athanassios G.; Dunlop, Patrick S. M.; Hamilton, Jeremy W. J.; Byrne, J. Anthony; O'Shea, Kevin; Entezari, Mohammad H.; Dionysiou, Dionysios D.
  Applied Catalysis, B: Environmental (2012), 125 (), 331-349CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
  A review. Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO2) semiconductor materials to split water into hydrogen and oxygen in a photo-electrochem. cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applications. One of the most significant scientific and com. advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 structure, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochem. and photoelectrochem. methods. Various applications of VLA TiO2, in terms of environmental remediation and in particular water treatment, disinfection and air purifn., are illustrated. Comprehensive studies on the photocatalytic degrdn. of contaminants of emerging concern, including endocrine disrupting compds., pharmaceuticals, pesticides, cyanotoxins and volatile org. compds., with VLA TiO2 are discussed and compared to conventional UV-activated TiO2 nanomaterials. Recent advances in bacterial disinfection using VLA TiO2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted.
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81. 81
  Huang, W.; Jing, Q.; Du, Y.; Zhang, B.; Meng, X.; Sun, M.; Schanze, K. S.; Gao, H.; Xu, P. An in Situ SERS Study of Substrate-Dependent Surface Plasmon Induced Aromatic Nitration J. Mater. Chem. C 2015, 3, 5285– 5291 DOI: 10.1039/C5TC00835B
  81
  An in situ SERS study of substrate-dependent surface plasmon induced aromatic nitration
  Huang, Wei; Jing, Qiang; Du, Yunchen; Zhang, Bin; Meng, Xiangli; Sun, Mengtao; Schanze, Kirk S.; Gao, Hong; Xu, Ping
  Journal of Materials Chemistry C: Materials for Optical and Electronic Devices (2015), 3 (20), 5285-5291CODEN: JMCCCX; ISSN:2050-7534. (Royal Society of Chemistry)
  Surface plasmon (SP)-induced nitration of arom. rings has been demonstrated by an in situ surface enhanced Raman spectroscopy (SERS) technique. The size feature of the as-prepd. Au, Ag and Ag@PDA@Au hierarchical structures allows monitoring the entire reaction process on a single hierarchical structure. With benzenethiol (BT) and HNO3 as reactants, SP induced arom. nitration can be successfully realized without the assistance of a conventional acid catalyst, H2SO4. Exptl. and theor. studies confirm that the nitration reaction leads to para-nitrothiophenol (p-NTP). While control expts. show that SP here functions as a local heating source and the presence of metal is also necessary for this nitration reaction. This SP induced arom. nitration reaction also displays SERS substrate-dependent reaction kinetics, which proceeds more rapidly on the Au surface. Higher laser power can generate a stronger photothermal effect, and thus an accelerated reaction rate for this reaction.
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82. 82
  Knight, M. W.; King, N. S.; Liu, L.; Everitt, H. O.; Nordlander, P.; Halas, N. J. Aluminium for Plasmonics ACS Nano 2014, 8, 834– 840 DOI: 10.1021/nn405495q
  82
  Aluminum for Plasmonics
  Knight, Mark W.; King, Nicholas S.; Liu, Lifei; Everitt, Henry O.; Nordlander, Peter; Halas, Naomi J.
  ACS Nano (2014), 8 (1), 834-840CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
  Unlike Ag and Au, Al has material properties that enable strong plasmon resonances spanning much of the visible region of the spectrum and into the UV. This extended response, combined with its natural abundance, low cost, and amenability to manufg. processes, makes Al a highly promising material for com. applications. Fabricating Al-based nanostructures whose optical properties correspond with theor. predictions, however, can be a challenge. The Al plasmon resonance is remarkably sensitive to the presence of oxide within the metal. For Al nanodisks, the energy of the plasmon resonance is detd. by, and serves as an optical reporter of, the percentage of oxide present within the Al. This understanding paves the way toward the use of Al as a low-cost plasmonic material with properties and potential applications similar to those of the coinage metals.
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83. 83
  McMahon, J. M.; Gray, S. K.; Schatz, G. C. Ultraviolet Plasmonics: The Poor Metals Al, Ga, In, Sn, Tl, Pb, and Bi Phys. Chem. Chem. Phys. 2013, 15, 5415– 5423 DOI: 10.1039/C3CP43856B
  83
  Plasmonics in the ultraviolet with the poor metals Al, Ga, In, Sn, Tl, Pb, and Bi
  McMahon, Jeffrey M.; Schatz, George C.; Gray, Stephen K.
  Physical Chemistry Chemical Physics (2013), 15 (15), 5415-5423CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  How the poor metals Al, Ga, In, Sn, Tl, Pb, and Bi can be used for plasmonics in the near to far UV range, similar to the noble metals Ag and Au in the visible (visible) range are discussed. The authors 1st discuss the empirical dielec. functions of the poor metals, contrasting them with Ag and Au, and also fitting them to a Drude and multiple Lorentz oscillator form. Using Mie theory, the authors then compare the optical responses of spherical poor metal nanoparticles to noble metal ones. Finally, nanoparticle dimers are studied using a vectorial finite element method. The poor metals exhibit large elec. field enhancements in the UV, comparable to Au in the visible, which makes them particularly attractive for sensing applications, such as surface enhanced Raman spectroscopy.
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84. 84
  Yin, P.-G.; Jiang, L.; You, T.-T.; Zhou, W.; Li, L.; Guo, L.; Yang, S. Surface-Enhanced Raman Spectroscopy with Self-Assembled Cobalt Nanoparticle Chains: Comparison of Theory and Experiment Phys. Chem. Chem. Phys. 2010, 12, 10781– 10785 DOI: 10.1039/c002662j
  There is no corresponding record for this reference.
85. 85
  Tian, Z.-Q.; Ren, B.; Li, J.-F.; Yang, Z.-L. Expanding Generality of Surface-Enhanced Raman Spectroscopy with Borrowing SERS Activity Strategy Chem. Commun. 2007, 34, 3514– 3534 DOI: 10.1039/b616986d
  There is no corresponding record for this reference.
86. 86
  Heck, K. N.; Janesko, B. G.; Scuseria, G. E.; Halas, N. J.; Wong, M. S. Observing Metal-Catalyzed Chemical Reactions in Situ Using Surface-Enhanced Raman Spectroscopy on Pd-Au Nanoshells J. Am. Chem. Soc. 2008, 130, 16592– 16600 DOI: 10.1021/ja803556k
  86
  Observing Metal-Catalyzed Chemical Reactions in Situ Using Surface-Enhanced Raman Spectroscopy on Pd-Au Nanoshells
  Heck, Kimberly N.; Janesko, Benjamin G.; Scuseria, Gustavo E.; Halas, Naomi J.; Wong, Michael S.
  Journal of the American Chemical Society (2008), 130 (49), 16592-16600CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Insight into the nature of transient reaction intermediates and mechanistic pathways involved in heterogeneously catalyzed chem. reactions is obtainable from a no. of surface spectroscopic techniques. Carrying out these investigations under actual reaction conditions is preferred but remains challenging, esp. for catalytic reactions that occur in water. Here, we report the direct spectroscopic study of the catalytic hydrodechlorination of 1,1-dichloroethene in H2O using surface-enhanced Raman spectroscopy (SERS). With Pd islands grown on Au nanoshell films, this reaction can be followed in situ using SERS, exploiting the high enhancements and large active area of Au nanoshell SERS substrates, the transparency of Raman spectroscopy to aq. solvents, and the catalytic activity enhancement of Pd by the underlying Au metal. The formation and subsequent transformation of several adsorbate species was obsd. These results provide the first direct evidence of the room-temp. catalytic hydrodechlorination of a chlorinated solvent, a potentially important pathway for groundwater cleanup, as a sequence of dechlorination and hydrogenation steps. More broadly, the results highlight the exciting prospects of studying catalytic processes in water in situ, like those involved in biomass conversion and proton-exchange membrane fuel cells.
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87. 87
  Mahmoud, M. A.; Garlyyev, B.; El-sayed, M. A. Controlling the Catalytic Efficiency on the Surface of Hollow Gold Nanoparticles by Introducing an Inner Thin Layer of Platinum or Palladium J. Phys. Chem. Lett. 2014, 5, 4088– 4094 DOI: 10.1021/jz502071v
  87
  Controlling the Catalytic Efficiency on the Surface of Hollow Gold Nanoparticles by Introducing an Inner Thin Layer of Platinum or Palladium
  Mahmoud, Mahmoud A.; Garlyyev, Batyr; El-Sayed, Mostafa A.
  Journal of Physical Chemistry Letters (2014), 5 (23), 4088-4094CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
  The efficiency of heterogeneous catalysis of electron-transfer reactions on the surface of gold nanoshells was changed by adding an inner platinum or palladium nanoshell in the double-shell nanocatalysts. The redn. of 4-nitrothiophenol (4NTP) by borohydride was studied as a model reaction. To confirm the heterogeneous catalytic mechanism, the nanocatalysts were assembled into a monolayer on the surface of a quartz substrate using the Langmuir-Blodgett technique, and the 4NTP was allowed to bind to the surface of gold through a strong thiol bond. The stages of the redn. reaction of 4NTP on the surface of gold were successfully followed by time-resolved surface-enhanced Raman spectroscopy. Palladium was found to increase the catalytic efficiency of the gold surface due to the presence of a new Fermi level of the palladium-gold alloy, while platinum decreased its catalytic efficiency due to the electron-withdrawing effect of platinum atoms, which resulted from the difference in their electrochem. redn. potentials.
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88. 88
  El-Aziz, A. M.; Kibler, L. A.; Kolb, D. M. The Potentials of Zero Charge of Pd(111) and Thin Pd Overlayers on Au(111) Electrochem. Commun. 2002, 4, 535– 539 DOI: 10.1016/S1388-2481(02)00362-4
  88
  The potentials of zero charge of Pd(1 1 1) and thin Pd overlayers on Au(1 1 1)
  El-Aziz, A. M.; Kibler, L. A.; Kolb, D. M.
  Electrochemistry Communications (2002), 4 (7), 535-539CODEN: ECCMF9; ISSN:1388-2481. (Elsevier Science B.V.)
  The potential of zero charge (pzc) of Pd(1 1 1) was detd. in dil. NaF solns. by measuring the Gouy-Chapman min. of the double-layer capacity. For a massive Pd(1 1 1) single crystal electrode a pzc of -0.12 V vs. SCE was found. The corresponding values for thin Pd(1 1 1) overlayers on Au(1 1 1) also were detd. While the pzc of the 1st, pseudomorphic Pd layer on Au(1 1 1) is -0.09 V vs. SCE, the pzc of a five monolayers thick Pd film on Au(1 1 1) is practically identical to the pzc of the massive Pd(1 1 1) electrode. By comparing pzc's and work functions for Au(1 1 1) and Pd(1 1 1), the dipole contribution to the potential drop across the Pd(1 1 1)/H2O interface is estd.
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89. 89
  Attard, G. A.; Bennett, J. A.; Mikheenko, I.; Jenkins, P.; Guan, S.; Macaskie, L. E.; Wood, J.; Wain, A. J. Semi-Hydrogenation of Alkynes at Single Crystal, Nanoparticle and Biogenic Nanoparticle Surfaces: The Role of Defects in Lindlar-Type Catalysts and the Origin of Their Selectivity Faraday Discuss. 2013, 162, 57– 75 DOI: 10.1039/c3fd00007a
  89
  Semi-hydrogenation of alkynes at single crystal, nanoparticle and biogenic nanoparticle surfaces: the role of defects in Lindlar-type catalysts and the origin of their selectivity
  Attard, G. A.; Bennett, J. A.; Mikheenko, I.; Jenkins, P.; Guan, S.; Macaskie, L. E.; Wood, J.; Wain, A. J.
  Faraday Discussions (2013), 162 (Fabrication, Structure and Reactivity of Anchored Nanoparticles), 57-75CODEN: FDISE6; ISSN:1359-6640. (Royal Society of Chemistry)
  For the first time, the method of shell-isolated nanoparticle Raman spectroscopy (SHINERS) is used in combination with cyclic voltammetry (CV) and reactivity studies to study the adsorption behavior of three alkynes undergoing hydrogenation on nanoparticle, single crystal and bacteria/graphite-supported platinum surfaces. A strong assocn. of alkynes with defect sites to produce a long-lived di-sigma/pi-alkene surface complex allows for deep hydrogenation of this intermediate to the alkane product. But when platinum surface defect sites are blocked by either bismuth or polyvinylpyrrolidone (PVP) (and thus leaving behind only Pt{111} terrace adsorption sites), large increases in selectivity to the semi-hydrogenation product are obsd. for all three alkynes. This finding is consistent with SHINERS collected from both well-ordered and roughened Pt{111} electrodes which revealed that the di-sigma/pi-bonded surface intermediate is hardly formed at all on Pt{111} unless defect sites are introduced via electrochem. roughening. As a general method of producing selective catalysts, the elimination of toxic heavy metals from Lindlar-type catalyst, used commonly in org. chem., and their replacement by more benign, org. species adsorbed at defect sites is discussed.
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90. 90
  Porter, M. D.; Lipert, R. J.; Siperko, L. M.; Wang, G.; Narayanan, R. SERS as a Bioassay Platform: Fundamentals, Design, and Applications Chem. Soc. Rev. 2008, 37, 1001– 1011 DOI: 10.1039/b708461g
  90
  SERS as a bioassay platform: fundamentals, design, and applications
  Porter, Marc D.; Lipert, Robert J.; Siperko, Lorraine M.; Wang, Gufeng; Narayanan, Radha
  Chemical Society Reviews (2008), 37 (5), 1001-1011CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
  A review. Bioanal. science is experiencing a period of unprecedented growth. Drivers behind this growth include the need to detect markers central to human and veterinary diagnostics at ever-lower levels and greater speeds. A set of parallel arguments applies to pathogens with respect to bioterrorism prevention and food and water safety. This tutorial review outlines the authors' recent explorations on the use of surface enhanced Raman scattering (SERS) for detection of proteins, viruses, and microorganisms in heterogeneous immunoassays. It will detail the design and fabrication of the assay platform, including the capture substrate and nanoparticle-based labels. The latter, which is the cornerstone of the authors' strategy, relies on the construction of gold nanoparticles modified with both an intrinsically strong Raman scatterer and an antibody. This labeling motif, referred to as extrinsic Raman labels (ERLs), takes advantage of the well-established signal enhancement of scatterers when coated on nanometer-sized gold particles, whereas the antibody imparts antigenic specificity. The authors will also examine the role of plasmon coupling between the ERLs and capture substrate, and challenges related to particle stability, nonspecific adsorption, and assay speed.
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91. 91
  Li, J. F.; Huang, Y. F.; Ding, Y.; Yang, Z. L.; Li, S. B.; Zhou, X. S.; Fan, F. R.; Zhang, W.; Zhou, Z. Y.; Wu, D. Y.; Ren, B.; Wang, Z. L.; Tian, Z. Q. Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy Nature 2010, 464, 392– 395 DOI: 10.1038/nature08907
  91
  Shell-isolated nanoparticle-enhanced Raman spectroscopy
  Li, Jian Feng; Huang, Yi Fan; Ding, Yong; Yang, Zhi Lin; Li, Song Bo; Zhou, Xiao Shun; Fan, Feng Ru; Zhang, Wei; Zhou, Zhi You; Wu, De Yin; Ren, Bin; Wang, Zhong Lin; Tian, Zhong Qun
  Nature (London, United Kingdom) (2010), 464 (7287), 392-395CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
  Surface-enhanced Raman scattering (SERS) is a powerful spectroscopy technique that can provide non-destructive and ultra-sensitive characterization down to single mol. level, comparable to single-mol. fluorescence spectroscopy. However, generally substrates based on metals such as Ag, Au and Cu, either with roughened surfaces or in the form of nanoparticles, are required to realize a substantial SERS effect, and this has severely limited the breadth of practical applications of SERS. A no. of approaches have extended the technique to non-traditional substrates, most notably tip-enhanced Raman spectroscopy (TERS) where the probed substance (mol. or material surface) can be on a generic substrate and where a nanoscale gold tip above the substrate acts as the Raman signal amplifier. The drawback is that the total Raman scattering signal from the tip area is rather weak, thus limiting TERS studies to mols. with large Raman cross-sections. Here, we report an approach, which we name shell-isolated nanoparticle-enhanced Raman spectroscopy, in which the Raman signal amplification is provided by gold nanoparticles with an ultrathin silica or alumina shell. A monolayer of such nanoparticles is spread as 'smart dust' over the surface that is to be probed. The ultrathin coating keeps the nanoparticles from agglomerating, separates them from direct contact with the probed material and allows the nanoparticles to conform to different contours of substrates. High-quality Raman spectra were obtained on various mols. adsorbed at Pt and Au single-crystal surfaces and from Si surfaces with hydrogen monolayers. These measurements and our studies on yeast cells and citrus fruits with pesticide residues illustrate that our method significantly expands the flexibility of SERS for useful applications in the materials and life sciences, as well as for the inspection of food safety, drugs, explosives and environment pollutants.
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92. 92
  Li, X.; Liu, M.; Lee, J.; Ding, D.; Bottomley, L. A.; Park, S.; Liu, M. An Operando Surface Enhanced Raman Spectroscopy (SERS) Study of Carbon Deposition on SOFC Anodes Phys. Chem. Chem. Phys. 2015, 17, 21112– 21119 DOI: 10.1039/C4CP05176A
  92
  An operando surface enhanced Raman spectroscopy (SERS) study of carbon deposition on SOFC anodes
  Li, Xiaxi; Liu, Mingfei; Lee, Jung-pil; Ding, Dong; Bottomley, Lawrence A.; Park, Soojin; Liu, Meilin
  Physical Chemistry Chemical Physics (2015), 17 (33), 21112-21119CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
  Thermally robust and chem. inert Ag@SiO2 nanoprobes are employed to provide the surface enhanced Raman scattering (SERS) effect for an in situ/operando study of the early stage of carbon deposition on nickel-based solid oxide fuel cell (SOFC) anodes. The enhanced sensitivity to carbon enables the detection of different stages of coking, offering insights into intrinsic coking tolerance of material surfaces. Application of a thin coating of gadolinium doped ceria (GDC) enhances the resistance to coking of nickel surfaces. The electrochem. active Ni-YSZ interface appears to be more active for hydrocarbon reforming, resulting in the accumulation of different hydrocarbon mols., which can be readily removed upon the application of an anodic current. Operando SERS is a powerful tool for the mechanistic study of coking in SOFC systems. It is also applicable to the study of other catalytic and electrochem. processes in a wide range of conditions.
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93. 93
  Li, X.; Lee, J.-P.; Blinn, K. S.; Chen, D.; Yoo, S.; Kang, B.; Bottomley, L. A.; El-Sayed, M. A.; Park, S.; Liu, M.

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Surface- and Tip-Enhanced Raman Spectroscopy in Catalysis
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