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Formation and Characterization of 2D Closely Packed Arrays of Bare Gold Nanoparticles without Aggregation
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  • Takashi Fujita
    Takashi Fujita
    Department of Applied Chemistry, School of Engineering, Tokyo University of Technology, 1401-1 Katakura, Hachioji, Tokyo 192-0982, Japan
    More by Takashi Fujita
  • Kohei Shibamoto*
    Kohei Shibamoto
    Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo 192-0397 Japan
    *Email: [email protected]. Phone: +81-42-677-2531.
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    Orcidhttps://orcid.org/0000-0003-2559-6739
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Cite this: ACS Omega 2022, 7, 49, 44711–44719
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https://doi.org/10.1021/acsomega.2c04032
Published November 30, 2022

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Abstract

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Uniform 2D arrays of metal nanoparticles (NPs) have received significant attention in the field of molecular sensing using localized surface plasmon resonance. Generally, metal NPs bear organic surface-modifying molecules to prevent aggregation and form 2D metal NP arrays. However, surface-modifying molecules negatively affect molecular sensing. Previously, we developed a technique for forming a 2D bare metal NP array, denoted the sandwich (SW) technique. However, the formation mechanism of these 2D metal NP arrays remains unknown and therefore the experimental conditions of the SW technique are not optimized. Here, we observed the formation of a 2D Au NP (d: 60 nm) array using the SW technique with an optical microscope. Moderate drying conditions of the colloidal droplets sandwiched between two parallel substrates were necessary for forming 2D Au NP arrays. We then optimized the drying conditions and obtained a 2D Au NP array. This array was uniform, and the Au NPs were arranged at distances of 4.5 nm with hexagonal periodicity, without aggregation. Further, the 2D Au NP arrays exhibited excellent spot-to-spot reproducibility in surface-enhanced Raman scattering.

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Introduction

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Metal nanoparticle (NP) assemblies have attracted considerable interest because of their exceptional optical properties based on localized surface plasmon resonance (LSPR), which is a collective oscillation of free electrons within the NPs. (1,2) Under LSPR excitation, excited electrons are localized on the surfaces of metal NPs. A strong electromagnetic (EM) field is generated from the surface at a distance similar to the diameter of the metal NP. The EM field is particularly strong at an interparticle gap of several nanometers, denoted as a “hot spot”, owing to the coupling of LSPRs between adjacent NPs. (3) This large EM field significantly increases the spectroscopic signals of molecules in the vicinity of metal NPs. For example, Raman scattering light of molecules is significantly enhanced in the vicinity of metal NPs by several orders of magnitude compared to normal Raman scattering light, which is called surface-enhanced Raman scattering (SERS). SERS allows the label-free identification of ultra-trace molecules. Therefore, metal NP assemblies with high-density hot spots exhibit potential as highly sensitive molecular sensors. (4,5) However, high-density hot spots are likely to cause randomness in the strength of the EM field because the EM field strength at the hot spot is sensitive to the interparticle distance. This randomness due to the nanostructure significantly reduces the spot-to-spot reproducibility in molecular sensing. (6,7) Therefore, the fabrication of uniform metal NP assemblies is required.
2D metal NP arrays, wherein metal NPs are densely arranged at equal interparticle distances of several nanometers, are promising candidates for generating such uniform metal NP assemblies. Two approaches are proposed for the design of 2D metal NP arrays. A top-down approach such as electron or ion beam lithography yields precise metal NP arrays, (8,9) but a method of generating hot spots at interparticle gaps is physically and technically challenging due to their spatial resolution. In addition, this approach generally requires large equipment and is costly. The other approach is a bottom-up approach, wherein metal NPs are assembled using a colloidal solution at liquid–liquid, (10,11) air–liquid, (12,13) or liquid–solid (14,15) interfaces. In principle, this approach may form hot spots at interparticle gaps because the interaction length of interparticle repulsion between NPs in solution is of several nanometers. Moreover, it is a low-cost approach and is suitable for mass production. Hence, the bottom-up approach is promising for producing 2D metal NP arrays for use in molecular sensing, but forming a uniform 2D metal NP array remains quite challenging.
The difficulty in forming a uniform 2D metal NP array using a bottom-up approach is mainly due to the aggregation of metal NPs, which renders the interparticle distance uncontrollable. According to Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, the dispersion or aggregation of particles is determined by the energy potential expressed by the sum of van der Waals attraction and electrostatic repulsion, which depend on the interparticle distance. (16) Metal particles exhibit relatively strong van der Waals attractions compared to those of non-metal particles and thus easily aggregate. Relatively large metal NPs, in particular, with diameters of 50–100 nm, which exhibit relatively large SERS enhancement, (17,18) are more likely to aggregate because they display larger van der Waals attractions than those of small metal NPs. To prevent aggregation of metal NPs, their surfaces are generally modified using organic molecules, such as alkanethiol, (19−21) or cetyltrimethylammonium bromide. (22) However, their introduction on the metal NPs causes several disadvantages and degrades the NP properties, such as shortening the lifetimes of 2D metal NP arrays, inhibiting sample molecule entry into hot spots, and hindering sample identification due to their SERS signals. (23,24) Uniform 2D metal NP arrays without organic surface-modified molecules are desirable in molecular sensing; however, reports on bare uniform 2D metal NP arrays are limited.
To suppress the aggregation of bare metal NPs, the repulsion should dominate the van der Waals attraction until just prior to metal NP assembly. We previously suppressed the aggregation of bare Au NPs trapped at a liquid–liquid interface using the LSPR excitation of Au NPs to enhance the repulsion during the 2D Au NP array formation. (25) However, aggregation was not eliminated because a 3D fluctuation of the liquid–liquid interface interfered with the ordered assembly of the Au NPs. Thus, the key to forming a 2D bare metal NP array without aggregation is the assembly of metal NPs on a rigid surface as gently as possible without disturbing the attraction–repulsion balance between the metal NPs.
In addition, we developed another technique for assembling bare metal NPs at a liquid–solid interface, denoted as the “sandwich (SW) technique.” (26) The SW technique may yield 2D arrays of bare metal NPs with diameters of 5–200 nm by naturally drying the droplet of metal NP colloidal solution between two flat plates until complete evaporation. However, the formation mechanism of the 2D metal NP array remains unclear, and accordingly the experimental conditions of the SW technique are not optimized. Consequently, this technique exhibits low reproducibility in forming the 2D metal NP array, and the uniformity of the 2D metal NP array has not been evaluated. In this study, we initially determined the features of the formation of a 2D metal NP array by observing the formation via the SW technique using an optical microscope. Spherical Au NPs with diameters of 60 nm were used as the building blocks of the 2D metal NP array because of their excellent chemical stabilities and relatively high efficiencies of LSPR excitation. The drying conditions were then optimized. The 2D Au NP array was characterized using scanning electron microscopy (SEM) and ultraviolet–visible spectroscopy. Finally, to demonstrate the uniformity of the EM field generated on the 2D Au NP array and its potential as an optical molecular sensor, the spot-to-spot reproducibility of SERS was evaluated.

Experimental Section

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Preparations of Au NP Arrays

An aqueous colloidal solution of spherical Au NPs (diameter: 60 nm; density: 2.6 × 1010 particles/mL) with a narrow size distribution was purchased from British Biocell International (Cardiff, UK). Glass slides (thickness: 1 mm) were purchased from Matsunami Glass (Bellingham, WA, USA), and Si single crystals (100 μm) were purchased from Nilaco (Tokyo, Japan). These glass slides and Si single crystals were cleaned several times using acetone, methanol, and deionized water in an ultrasonic bath prior to use.
The colloidal solution of Au NPs (100 μL) was dropped onto a glass slide or Si single crystal. A glass slide was placed on top of the droplet, 1 mm from the bottom glass. The sandwiched droplet was placed in a thermo-hygrostat bath until the solution evaporated completely after ≤2 d. The substrate prepared using this technique is denoted as “SW substrate.” SW substrates were prepared under two sets of conditions: 60 ± 10% relative humidity at 298 K and 20 ± 5% relative humidity at 298 K for SW-substrates 1 and 2, respectively.
Two other substrates were prepared using oil–water trapping (OW) (10) and dried droplet (DD) techniques for comparison. In the OW technique, the colloidal Au NP solution (5 mL) was transferred into a 20 mL glass vial, and toluene (5 mL) was added. After an interface formed between the toluene and the Au NP colloidal solution, methanol (5 mL) was rapidly injected into the vial, inducing the 2D trapping of the Au NPs at the interface. Then, the trapped Au NP sheet was placed on a 5 × 5 mm glass slide by aspirating off the solvent. The prepared OW substrates were dried in a drying cabinet at 298 K. In the DD technique, the colloidal Au NP solution (400 μL) was dropped onto a glass slide, and it was dried in a drying cabinet at 298 K.
All substrates were rinsed with deionized water to eliminate inorganic surfactants and dried further in a drying cabinet at 298 K.

Characterizations of 2D Au NP Arrays

All the substrates were observed using SEM (VE-9800, Keyence, Itasca, IL, USA) at an accelerating voltage of 20 kV. Visible–near-infrared (vis–NIR) extinction spectroscopy was performed under normal incidence conditions using a custom-built optical system connected to a spectrometer combined with an optical microscope. The focal spot diameter was confirmed using an optical microscope as ∼100 μm.
A custom-built system was also used to conduct the Raman measurements using a 532 nm Nd:YAG laser as an excitation source. The laser power at the sample position was 5 mW, with a laser focal spot of ∼10 μm2. Raman spectroscopy was performed using a −15 °C air-cooled spectrometer (PMA-11, Hamamatsu Photonics, Hamamatsu, Japan) that was connected to a detector. Crystal violet (CV) was used as a test molecule to perform SERS investigations. Each prepared substrate was immersed in a 10–5 M CV aqueous solution for 10 min to achieve saturated adsorption of CV. The substrates were then rinsed with pure water to remove any non-chemisorbed CV molecules. The Raman spectra of the adsorbed CV molecules were recorded by integrating five spectra with an exposure time of 10 s. The difference in the focus of the different substrates was calibrated using a Si band (520 cm–1). The spectral signal representing CV is due to SERS light and fluorescence. The fluorescence component was removed from the raw data using the fluorescence spectrum of solid CV, and the intensity of the Raman scattered light was extracted.

Results and Discussion

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Formation of 2D Au NP Arrays Using the SW Technique

The formation of a 2D Au NP array using the SW technique was observed using an optical microscope. Figure 1a shows an optical microscopy image of the lateral meniscus formed by the SW technique. The meniscus exhibits a half-moon shape, which differs from those of simple droplets on a flat plate. The contact angle of the meniscus is 0°. Figure 1b shows the images of the contact line at 30 min intervals during the initial evaporation stages. At t = 45 min, the contact line is red due to the LSPR of the isolated Au NPs. The color of the contact line darkens with time until t = 45 min, with this color change corresponding to an increase in the concentration of the Au NP colloidal solution, that is, as the droplet evaporates, the Au NPs are concentrated at the edge of the contact line. From t = 45 to 105 min, the color of the contact line changes from red to deep purple. To observe this color change more clearly, the contact line at t = 45 min was observed using a reflection optical microscope, as shown in Figure 1c. A color gradation from red to gold is observed at the edge of the contact line. This gold color corresponds to an assembly of Au NPs, as confirmed by the SEM observations described below, indicating that the 2D Au NP array is formed at the edge of the contact line. At t = 105 min, the formation of a step-by-step structure is observed, corresponding to the structure observed using SEM (Figure 2a). This step-by-step structure indicates a gradual inward movement of the contact line because the 2D Au NP array is only formed at the edge of the contact line. Hence, the Au NP array is formed by an increase in the concentration of Au NPs at the contact line and the movement of the contact line during droplet evaporation. Therefore, the duration of the sandwiched droplet appears to determine the properties of the 2D Au NP array, such as the density of Au NPs, aggregation, and stacking. In subsequent studies, the sandwiched droplet was dried in a thermo-hygrostat bath to stabilize and control the evaporation rate.

Figure 1

Figure 1. (a) Optical microscopy image of the lateral meniscus image formed by the SW method at 0 min from the start. Dotted circle indicates a contact line. (b) Optical microscopy image of the contact line in the initial evaporation process (0, 45, 75, and 105 min from the start). (c) Reflection microscopy image of the contact line at t = 45 min.

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Figure 2

Figure 2. (a) SEM image at ×50 magnification of SW-substrate 1 on the Si wafer, which was prepared at a relative humidity of 60 ± 10% at 298 K. (b) SEM image at ×20,000 magnification of SW-substrate 1. (c) SEM image at ×20,000 magnification of SW-substrate 2, which was prepared at a relative humidity of 20 ± 5% at 298 K. These substrates were composed of spherical Au NPs (mean diameter: 60 nm). Corresponding FFT images and their brightness distribution are shown in the higher right and lower right, respectively.

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Optimization of the Drying Conditions during the SW Technique

To analyze the effect of the evaporation rate on the formation of the 2D Au NP array, we prepared Au NP arrays using the SW technique at different temperatures and humidities. First, we examined the effect of temperature on the formation of 2D Au NP arrays. Figure S1a–c show SEM images (×10,000) of 2D Au NP arrays formed at a relative humidity of 60 ± 10% and temperatures of 293, 298, and 303 K, respectively. These SEM images reveal magnified views of the outermost steps of the step-by-step structures. Figure S1a shows a 2D Au NP array formed at a relatively low temperature, with large voids and several Au NP aggregates observed. Moreover, the Au NPs appear to be stacked on the left of the black centerline. Figure S1c shows a 2D Au NP array formed at a relatively high temperature, with numerous large Au NP aggregates observed.
Conversely, in Figure S1b, the 2D Au NP arrays appear to be monolayer, with almost no aggregation. Subsequently, humidity conditions were examined. Two 2D Au NP arrays prepared using the SW technique at 298 K with relative humidity of 60 ± 10% (SW-substrate 1) and 20 ± 5% (SW-substrate 2) were observed. Figure 2b shows an SEM image (×20,000) of SW-substrate 1, with the Au NPs observed in a dense 2D arrangement. Figure 2c shows an SEM image (×20,000) of SW-substrate 2. At this humidity, the evaporation rate is double that observed at a relative humidity of 60%. Numerous small islands consisting of several Au NPs are observed, and the distances between each island are several tens of nanometers. The density of Au NPs in SW-substrate 2 is lower than that in SW-substrate 1. Therefore, the optimal temperature and relative humidity are 298 K and 60 ± 10%, respectively. Moreover, the quality of the 2D Au NP array is highly and sensitively dependent on the drying temperature and humidity.
For comparison,Two substrates were also prepared using the OW and DD methods . Figure 3a shows an SEM image (×2000) of the OW-substrate, with several defects and 3D aggregates observed. Figure 3b shows an SEM image (×20,000) of the DD-substrate, with isolated Au NPs and several Au NP aggregates scattered randomly.

Figure 3

Figure 3. (a) SEM image at ×20,000 magnification of the OW-substrate on the Si wafer. (b) SEM image at ×20,000 magnification of the DD-substrate on Si wafer. These substrates were composed of spherical Au NPs (mean diameter: 60 nm). Corresponding FFT images and their brightness distribution are shown in the higher right and lower right, respectively.

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Characterizations of 2D Au NP Arrays

The obtained SEM images were divided into 500 × 500 nm regions to evaluate the densities and uniformities of the 2D Au NP arrays. The packing densities in each region were determined using the areas of the Au NPs. Table 1 summarizes the packing densities and their relative standard deviations (RSDs, n = 96). The packing densities of the Au NPs are ordered as follows: SW-substrate 1 (78%) > SW-substrate 2 (73%) > OW-substrate (65%) > DD-substrate (16%). Their RSDs are ordered as follows: SW-substrate 1 (3.1%) < SW-substrate 2 (5.5%) < OW-substrate (6.1%) < DD-substrate (71%). Compared to those of OW and DD substrates, the SW substrates exhibit high Au NP densities and uniformities. Additionally, SW-substrate 1 exhibits a higher density and uniformity than those of SW-substrate 2 due to the effect of humidity on the evaporation rate of the Au NP colloidal solution.
Table 1. Packing Densities and Their RSDs of Four Substrates
substratepacking density (%)RSD (%)
SW-substrate 1783.1
SW-substrate 2735.5
OW-substrate656.1
DD-substrate1671
A highly uniform particle array likely exhibits a periodic array structure, and Fourier transform (FT) analyses were performed on SEM images to evaluate the periodicities of the arrangements. Figure 2b,c show the FTs of the SEM data of SW-substrates 1 and 2, respectively. Bright spots are observed in these two images at the vertices of hexagons. Therefore, SW-substrates 1 and 2 exhibit periodicities of six-fold symmetry. However, the packing density of 78% observed for SW-substrate 1 is smaller than that of 91% expected for an ideal 2D hexagonal close-packed structural configuration. The FT of SW-substrate 1 data was then analyzed to explain this difference. The hexagonal lattice constant of SW-substrate 1 is 64.5 nm. Because the Au NPs exhibit an average diameter of 60 nm, this indicates that the Au NPs in SW-substrate 1 are not in contact with each other, with an average interparticle distance of ∼4.5 nm. When the interparticle distance is 4.5 nm, the ideal packing density of a 2D hexagonal-packed configuration is 81%. The 3% difference in the recalculated (81%) and experimental (78%) packing densities of SW-substrate 1 may be attributed to minor defects. Conversely, as shown in Figure 3a,b, no such bright spots are observed in the FT images of the other substrates. These Au NP assemblies in the OW and DD substrates exhibit no periodicities.
Figure 4 shows the vis–NIR extinction spectra of SW-substrate 1 (black line), the OW and DD substrates (green and red lines, respectively), and Au NP colloidal solution (dotted line). The spectrum of SW-substrate 1 exhibits two peaks at 547 and 750 nm. The spectrum of the OW substrate exhibits a broad peak in the region 600–1000 nm, whereas that of the DD substrate exhibits a single peak at 540 nm. The spectrum of the Au NP colloidal solution exhibits a single peak at 537 nm, corresponding to the LSPR of isolated spherical Au NPs in water. The peaks at 547 and 540 nm in the spectra of SW-substrate 1 and the DD substrate, respectively, may be attributed to the red-shifted LSPR peak representing isolated spherical Au NPs. Therefore, either most Au NPs in SW-substrate 1 and the DD substrate are isolated from their neighbors or the numbers and sizes of the aggregated Au NPs are small. This is consistent with the SEM observations and the FT analyses. The red-shift distance from the isolated spherical Au NP LSPR peak to that observed for SW-substrate 1 is 10 nm, whereas the shift distance to that observed for the DD substrate is 3 nm. The LSPR peak wavelength depends on the plasmonic coupling of neighboring Au NPs. Therefore, the large red-shift observed for SW-substrate 1 is due to plasmonic coupling. For SW-substrate 1, a peak at 750 nm is also observed. When several Au NPs are close, with interparticle distances of several nanometers, an additional peak is observed at a longer wavelength in the vis–NIR extinction spectrum. Hentschel et al. showed that the extinction spectra of Au NP heptamers with interparticle gaps exhibited new extinction peaks in the NIR region when the gap distance was <60 nm. (27) They concluded that this additional extinction peak was caused by a plasmonic oligomer transition from isolated to collective modes. Although there are several differences between the experimental conditions in this study and those of other groups, the previously reported extinction spectra are similar to those of SW-substrate 1. Therefore, the peak in the spectrum of SW-substrate 1 at 750 nm is due to LSPR coupling. For the OW substrate, the LSPR peak representing the isolated Au NPs almost entirely disappears, with a broad peak emerging from 600 to 1000 nm. When Au NPs aggregate randomly, these aggregates exhibit broad, longer wavelength peaks due to their various plasmon modes. Therefore, the spectrum of the OW substrate indicates that almost all Au NPs are randomly aggregated.

Figure 4

Figure 4. Vis–NIR Extinction spectra of (a) SW-substrate 1, (b) OW-substrate, and (c) DD-substrate. These substrates were on glass slides. The dotted line indicates vis–NIR absorption spectra of spherical Au NP (mean diameter: 60 nm) colloidal solution, which was used for the preparation of these substrates.

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SERS Properties of 2D Au NP Arrays

To investigate the SERS properties of SW-substrate 1, CV was used as a test molecule because it is well studied in SERS. (28,29) Here, uniform adsorption of CV on the Au NP surfaces was required to evaluate the spot-to-spot reproducibility of SERS signals representing the nanostructures of the SERS substrates. CV molecules are chemically adsorbed on the surface of Au. Thus, by immersing the SERS substrate in the CV solution, the CV molecules may be chemically adsorbed on the surfaces of the Au NPs as a monolayer after washing and removing the physically adsorbed CV molecules. The immersion time was determined via SERS measurements using OW substrates (Figure S2), and the immersion time for saturation adsorption was set at 1000 s. Figure 5a shows the Raman spectrum of CV molecules chemically adsorbed on SW-substrate 1 at an excitation wavelength of 532 nm, and Table 2 shows the assignments of these peaks in previous studies. (30)

Figure 5

Figure 5. (a) Raman spectra of CV adsorbed on SW-substrate 1 and (b) Raman spectra of CV crystals. 532 nm lines of Nd:YAG laser was employed as the excitation laser.

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Table 2. Assignment of Raman Bands of CV Crystal and CV Adsorbed on SW-Substrate 1
band (cm–1) crystalband (cm–1) on SW substrate 1assignment
16201621C-phenyl in-plane antisymmetric stretching
15831584C-phenyl in-plane antisymmetric stretching
15321537phenyl-N antisymmetric stretching
13761380C–N, phenyl-C-phenyl antisymmetric stretching
11751179C-phenyl, C–H in-plane antisymmetric stretching
No signals other than those derived from CV molecules were observed. This result suggests that no molecules other than sample CV molecules are adsorbed on the Au NPs’ surface and that the Au NPs are bare, at least after substrate fabrication. In addition, we have previously reported that laser desorption/ionization mass spectrometry detects surface adsorbed species on the Au NPs with high sensitivity. (31) Like the present study, when CV molecules were adsorbed on gold NPs, no signals other than CV molecules were observed in either the positive or negative ion mode. This report also supports that the Au NPs are bare after washing with water.
To estimate the SERS enhancement factor (EF) of SW-substrate 1, the number of CV molecules adsorbed on the Au NPs was calculated using the surface area, packing density, irradiation area of the laser, and adsorption area of CV. The most prominent peak at 1621 cm–1 was used to perform the EF calculations. The laser irradiation area was 10 μm2, and the CV molecules were approximated as circles with diameters of ∼1 nm. Assuming that CV molecules were adsorbed to the upper half of an Au NP, 7200 CV molecules were adsorbed per Au NP. The number of CV molecules contributing to the Raman signal was 107–108 molecules per spot, or 1.7 × 10–16 mol. The typical Raman spectrum of the CV crystal (from 1012 to 1013 molecules per spot) was also measured, as shown in Figure 5b. Therefore, the average EF of SW-substrate 1 was 105–106. The EFs were within the range of average reported values for Au NPs on a solid substrate (104–108). (32,33) Furthermore, the OW and DD substrates exhibited sufficient SERS activities at certain points. However, the average EFs of these substrates were 1–2 orders of magnitude lower than that of SW-substrate 1.
The spot-to-spot reproducibility of SW-substrate 1 was then examined for three prominent bands at 1179, 1380, and 1621 cm–1. Figure 6a–c show the normalized peak intensity of each CV band in the SERS spectra measured at 32 different points on the same substrate, and Figure 6d shows their RSDs. The packing density is used as a uniformity index to compare the different substrates and is set as the horizontal axis. As the packing density increases, the variation in the peak intensity of each band decreases, and those observed for SW-substrate 1, with a packing density of 78%, exhibit the smallest value (3.1%). This RSD value is lower than previous SERS studies using Au NPs shown in Table S3, indicating very high spot-to-spot reproducibility, although simple comparisons are difficult due to the different experimental conditions. Surprisingly, the RSD of SW-substrate 1 is similar to that of a systematic error obtained by a spot-to-spot Raman measurement on a Si single crystal, as shown in Figure 6d. Therefore, a sufficiently uniform EM field is generated over the entire SW-substrate 1 for a spot area of ∼10 μm2. In addition, as the packing density increases, the RSD decreases significantly.

Figure 6

Figure 6. Normalized peak intensities of bands at (a) 1179 cm–1, (b) 1380 cm–1, and (c) 1621 cm–1 versus packing rates of four substrates. The mean value was normalized to 1 (dotted line). These peak intensities were obtained from different 25 spots in these substrates. (d) RSDs of SERS intensities at 1621 cm–1 versus packing rates of four substrates. The dotted line indicates the systematic error obtained from a silicon single crystal (100).

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The improvement in reproducibility due to the increased packing ratio varies according to the band. The improvement in reproducibility of the band at 1621 cm–1 is particularly remarkable. Although the cause of this remains unclear, these differences are likely caused by the adsorption states of the CV molecules and their associated charge transfer (CT) enhancement, (34) which is observed for molecules chemisorbed on a bare metal surface. According to previous reports, (35,36) these factors exhibit different effects on each vibration band associated with chemisorption. As shown in Table 2, shifts due to chemisorption are observed in several vibration bands, with varying degrees of shifting. However, the band at 1621 cm–1 is not significantly shifted. Thus, the effects of CV molecule adsorption and CT enhancement on the band at 1621 cm–1 are relatively small. The EM enhancement may be relatively high for the 1621 cm–1 band, and the high uniformity of SW-substrate 1 directly reflects the reproducibility. A more detailed study should be conducted to study the contribution of CT enhancement to the reproducibility of SERS measurements.

Mechanistic Considerations of the SW Technique

A series of studies revealed that SW-substrate 1 exhibits a uniform arrangement without Au NP aggregation, although organic surface-modifying molecules are not used to modify the Au NP surfaces. Furthermore, the high spot-to-spot reproducibility of the SERS measurements supports the high uniformity of the nanostructure of SW-substrate 1. We investigated the formation of this array by observing the formation of the 2D Au NP array and the final array structure using an optical microscope.
In the early stage of evaporation at t = 45 min, the Au NPs are concentrated on the contact line, as shown in Figure 1a. In general, the solute reaches equilibrium at a uniform concentration via diffusion within the solution. Therefore, this non-equilibrium state is due to a mechanism, such as convection, which supplies Au NPs to the edge of the contact line. In addition, as shown in Figure 1a, the contact angle is 0° at the edge of the contact line. This sharp contact line hinders the formation of 3D aggregates because the height of the droplet at the edge is insufficient for supplying Au NPs to the second layer at the edge of the contact line. No stacking is observed under the optimized drying conditions.
Au NPs concentrated at the edge of the contact line remain dispersed in the liquid before forming the 2D Au NP array, as shown in Figure 1c. According to calculations based on DLVO theory, the potential barriers of Au NPs dispersed in water are located at an interparticle distance of several nanometers, and they aggregate when they are closer than the potential barrier. Because no aggregation is observed in SW-substrate 1, the Au NPs may maintain a state wherein the repulsion between the particles dominates until the 2D Au NP array is formed, with the kinetic energy not exceeding the potential barrier. On the other hand, formation of numerous aggregates when the SW technique is performed at 303 K, a relatively high temperature, as shown in Figure S1. We considered that the kinetic energy exceeds the potential barrier at this temperature, thus causing aggregation.
Smooth movement of the contact line is observed with the formation of the 2D Au NP array, as shown in Figure 1b. Generally, the contact line of a simple droplet on a flat plate is pinned, maintaining its initial position when the solvent dries. In this case, the solute concentrates at the contact line, forming a ring, denoted the coffee-ring effect. (37) This causes a concentration of the solute at the edges of the droplet, leading to aggregation. However, during the SW technique, the pinning of the contact line is suppressed. The movement of the contact line is more likely to occur than the shape variation of the meniscus that is stabilized in the capillary bridge. This movement of the contact line prevents a supply of excess Au NPs to the contact line and suppresses the aggregation of the Au NPs.
In summary, we considered three factors contributing to the formation of a uniform 2D Au NP array using the SW technique. First, Au NPs were supplied to the edge of the sharp contact line. Second, the Au NPs were gently concentrated without energy addition. Third, the half-moon meniscus moved as the droplet dried, without pinning the contact line. These factors depended on the drying conditions, such as the temperature and humidity. Under suitable drying conditions, the Au NPs were concentrated at the edge of the contact line while maintaining the repulsion between particles. As a result, the Au NP arrangement was highly ordered, without aggregation, and without an organic surface modifier. The step-by-step structures observed in Figures 1b and 2a were formed due to the balance between the supply rate of Au NPs to the edge of the contact line and the rate of motion of the contact line.

Conclusions

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We investigated the SW technique to form uniform 2D bare Au NP arrays using colloidal dispersions of Au NPs. First, the formation of the 2D Au NP arrays using the SW technique was observed using an optical microscope to determine the effective synthetic parameters of a uniform 2D bare Au NP array. The supply of Au NPs to the edge of the contact line and the formation of the Au NP assembly were observed as the droplets dried. Based on these observations, we focused on and optimized the drying conditions. The most uniform 2D Au NP array was formed at 298 K and a relative humidity of 60%. SW-substrate 1 formed under the optimized conditions exhibited a hexagonal closely packed structure with an average interparticle distance of 4.5 nm without aggregation. Although the ideal densest packing ratio in this case was 81%, the packing ratio of SW-substrate 1 was 78%, indicating a very high packing ratio. In the extinction spectrum of SW-substrate 1, peaks due to the LSPR of the Au NPs and plasmon coupling were observed. Compared to those of conventional 2D Au NP arrays, such as the DD and OW substrates, the uniformity of the SW substrate was extremely high. Furthermore, the SW substrate showed excellent SERS enhancement, with an RSD of 3.1% for its signal intensity, which is comparable to the systematic error of the present Raman measurements, indicating a very high spot-to-spot reproducibility. To the best of our knowledge, the SW technique is the simplest method that enables the formation of a uniform 2D bare Au NP array with interparticle gaps. In the future, it may be possible to control the interparticle gap by controlling the repulsion between the NPs. Thus, use of the SW technique may lead to the development of molecular sensors and plasmonics..

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.2c04032.

  • SEM images of SW substrates, dependence of Raman peak intensity on the dipping time, and literature data for SERS substrates using Au NPs (DOCX)

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Author Information

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  • Corresponding Author
  • Author
    • Takashi Fujita - Department of Applied Chemistry, School of Engineering, Tokyo University of Technology, 1401-1 Katakura, Hachioji, Tokyo 192-0982, Japan
  • Author Contributions

    The manuscript was written through contributions of all authors. All authors have given their approval to the final version of the manuscript.

  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This work was supported by JSPS KAKENHI grant no. JP18K04730 (K.S.) and JSPS KAKENHI grant no. JP19K15410 (T.F.).

Abbreviations

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CT

charge transfer

CV

crystal violet

DD

dried droplet

DLVO

Derjaguin–Landau–Verwey–Overbeek

EF

enhancement factor

EM

electromagnetic

FT

Fourier transform

LSPR

localized surface plasmon resonance

NP

nanoparticle

OW

oil–water trapping

RSD,

relative standard deviation;

SEM

scanning electron microscopy

SERS

surface-enhanced Raman scattering

SW

sandwich

vis–NIR

visible–near-infrared

References

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This article references 37 other publications.

  1. 1
    Mayer, K. M.; Hafner, J. H. Localized Surface Plasmon Resonance Sensors. Chem. Rev. 2011, 111, 3828– 3857,  DOI: 10.1021/cr100313v
    Google Scholar
    1
    Localized surface plasmon resonance sensors
    Mayer, Kathryn M.; Hafner, Jason H.
    Chemical Reviews (Washington, DC, United States) (2011), 111 (6), 3828-3857CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. Topics include physics of localized surface plasmon resonance (LSPR); sensing with LSPR, effect of particle size, shape, and material; LSPR-based biol. and chem. sensors; technol. advances in LSPR sensing; maximizing the mol. detection sensitivity of LSPR; and future directions like mol. biol. or diagnostic tool application.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXntVenuro%253D&md5=d7c4707f001eb497bfb4945f35729e83
  2. 2
    Jiang, N.; Zhuo, X.; Wang, J. Active Plasmonics: Principles, Structures, and Applications. Chem. Rev. 2018, 118, 3054– 3099,  DOI: 10.1021/acs.chemrev.7b00252
    Google Scholar
    2
    Active Plasmonics: Principles, Structures, and Applications
    Jiang, Nina; Zhuo, Xiaolu; Wang, Jianfang
    Chemical Reviews (Washington, DC, United States) (2018), 118 (6), 3054-3099CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review. Active plasmonics is a burgeoning and challenging subfield of plasmonics. It exploits the active control of surface plasmon resonance. In this review, a first-ever in-depth description of the theor. relationship between surface plasmon resonance and its affecting factors, which forms the basis for active plasmon control, will be presented. Three categories of active plasmonic structures, consisting of plasmonic structures in tunable dielec. surroundings, plasmonic structures with tunable gap distances, and self-tunable plasmonic structures, will be proposed in terms of the modulation mechanism. The recent advances and current challenges for these three categories of active plasmonic structures will be discussed in detail. The flourishing development of active plasmonic structures opens access to new application fields. A significant part of this review will be devoted to the applications of active plasmonic structures in plasmonic sensing, tunable surface-enhanced Raman scattering, active plasmonic components, and electrochromic smart windows. This review will be concluded with a section on the future challenges and prospects for active plasmonics.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhsFOht7rO&md5=11b74d2e960d98218055db96d4b987b0
  3. 3
    Kleinman, S. L.; Frontiera, R. R.; Henry, A. I.; Dieringer, J. A.; Van Duyne, R. P. Creating, Characterizing, and Controlling Chemistry with SERS Hot Spots. Phys. Chem. Chem. Phys. 2013, 15, 21– 36,  DOI: 10.1039/c2cp42598j
    Google Scholar
    3
    Creating, characterizing, and controlling chemistry with SERS hot spots
    Kleinman, Samuel L.; Frontiera, Renee R.; Henry, Anne-Isabelle; Dieringer, Jon A.; Van Duyne, Richard P.
    Physical Chemistry Chemical Physics (2013), 15 (1), 21-36CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    A review. In this perspective the roles of hot spots in surface-enhanced Raman spectroscopy (SERS) are discussed. After giving background and defining the hot spot, the authors evaluate a variety of SERS substrates which often contain hot spots. The authors compare and discuss the differentiating properties of each substrate. The authors then provide a thorough anal. of the hot spot contribution to the obsd. SERS signal both in ensemble-averaged and single-mol. conditions. The authors also enumerate rules for detg. the SERS enhancement factor (EF) to clarify the use of this common metric. Finally, the authors present a forward-looking overview of applications and uses of hot spots for controlling chem. on the nanoscale. Although not exhaustive, this perspective is a review of some of the most interesting and promising methodologies for creating, controlling, and using hot spots for electromagnetic amplification.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhvVSmtbbE&md5=11207d7bf20e11694586b92baf29e183
  4. 4
    Sharma, B.; Frontiera, R. R.; Henry, A. I.; Ringe, E.; Van Duyne, R. P. SERS: Materials, Applications, and the Future. Mater. Today 2012, 15, 16– 25,  DOI: 10.1016/S1369-7021(12)70017-2
    Google Scholar
    4
    SERS: Materials, applications, and the future
    Sharma, Bhavya; Frontiera, Renee R.; Henry, Anne-Isabelle; Ringe, Emilie; Van Duyne, Richard P.
    Materials Today (Oxford, United Kingdom) (2012), 15 (1-2), 16-25CODEN: MTOUAN; ISSN:1369-7021. (Elsevier Ltd.)
    A review. Surface enhanced Raman spectroscopy (SERS) is a powerful vibrational spectroscopy technique that allows for highly sensitive structural detection of low concn. analytes through the amplification of electromagnetic fields generated by the excitation of localized surface plasmons. SERS has progressed from studies of model systems on roughened electrodes to highly sophisticated studies, such as single mol. spectroscopy. We summarize the current state of knowledge concerning the mechanism of SERS and new substrate materials. We highlight recent applications of SERS including sensing, spectroelectrochem., single mol. SERS, and real-world applications. We also discuss contributions to the field from the Van Duyne group. This review concludes with a discussion of future directions for this field including biol. probing with UV-SERS, tip-enhanced Raman spectroscopy, and ultrafast SERS.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XivV2gur0%253D&md5=e98456c30aac49486c41e9c5ac960369
  5. 5
    Huang, Z.; Zhang, A.; Zhang, Q.; Cui, D.; Nanomaterial-Based, S. E. R. S. Nanomaterial-Based SERS Sensing Technology for Biomedical Application. J. Mater. Chem. B 2019, 7, 3755– 3774,  DOI: 10.1039/C9TB00666D
    Google Scholar
    5
    Nanomaterial-based SERS sensing technology for biomedical application
    Huang, Zhicheng; Zhang, Amin; Zhang, Qian; Cui, Daxiang
    Journal of Materials Chemistry B: Materials for Biology and Medicine (2019), 7 (24), 3755-3774CODEN: JMCBDV; ISSN:2050-7518. (Royal Society of Chemistry)
    Over the past few years, nanomaterial-based surface-enhanced Raman scattering (SERS) detection has emerged as a new exciting field in which theor. and exptl. studies of the structure and function of nanomaterials have become a focus. The importance of different dimensional nanomaterials has begun to be recognized, esp. in the fundamental development of SERS sensing detection for biomedical application. Great advances have been and are being made in different dimensional nanomaterial-based SERS technol. with enormous prospects in clin. medicine applications. Herein we review some of the main advances in this field over the past few years, explore the application prospects, and discuss the concepts, issues, approaches and challenges, with the aim of stimulating broader interest in developing nanomaterial-based SERS sensing applications for medical theranostics.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtVegur%252FK&md5=72bc6274a36c959d5dd4f8af1e838328
  6. 6
    Sackmann, M.; Materny, A. Surface Enhanced Raman Scattering (SERS) – A Quantitative Analytical Tool?. J. Raman Spectrosc. 2006, 37, 305– 310,  DOI: 10.1002/jrs.1443
    Google Scholar
    6
    Surface enhanced Raman scattering (SERS) - a quantitative analytical tool?
    Sackmann, M.; Materny, A.
    Journal of Raman Spectroscopy (2006), 37 (1-3), 305-310CODEN: JRSPAF; ISSN:0377-0486. (John Wiley & Sons Ltd.)
    Raman spectroscopy is a widely used anal. tool capable of providing valuable information about the chem. structure and compn. of mols. In order to detect substances also at a very low concn. levels, Surface Enhanced Raman Scattering (SERS) was introduced. The different amplification mechanisms result in extreme sensitivity, however, a quant. use of SERS appears to be problematic. Esp., when deploying silver sols as SERS substrates, the reproducibility of the signal intensities for a given substance concn. is questionable. Exptl. results of an investigation of this problem for low concns. of adenine are presented. Comparison with results obtained for different SERS substrates by other authors reveals clearly different dependencies. Only in a very limited concn. range reproducible and therefore quant. utilizable data could be obtained.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhsFWgsLg%253D&md5=ce363b0eaa67784fba7e97a704a4382f
  7. 7
    De Rosa, C.; Auriemma, F.; Diletto, C.; Di Girolamo, R.; Malafronte, A.; Morvillo, P.; Zito, T.; Rusciano, G.; Pesce, G.; Sasso, A. Toward hyperuniform disordered plasmonic nanostructures for reproducible surface-enhanced Raman spectroscopy. Phys. Chem. Chem. Phys. 2015, 17, 8061– 8069,  DOI: 10.1039/c4cp06024e
    Google Scholar
    7
    Toward hyperuniform disordered plasmonic nanostructures for reproducible surface-enhanced Raman spectroscopy
    De Rosa, C.; Auriemma, F.; Diletto, C.; Di Girolamo, R.; Malafronte, A.; Morvillo, P.; Zito, G.; Rusciano, G.; Pesce, G.; Sasso, A.
    Physical Chemistry Chemical Physics (2015), 17 (12), 8061-8069CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    The authors report on the self-assembling of clusters of Au-nanoparticles (Au-NPs) directed by the phase sepn. of poly(styrene)-b-poly(methylmethacrylate) (PS-b-PMMA) block-copolymer (BCP) on In Sn oxide coated glass, which induces the onset of vertical lamellar domains. After thermal evapn. of Au on BCP, Au-NPs of 4 nm are selectively included into PS-nanodomains by thermal annealing, and then clustered with large d. of hot spots (> 104 μm2) in a random 2-dimensional pattern. The resulting nanostructure exhibits near-hyperuniform long-range correlations. The consequent large degree of homogeneity of this isotropic plasmonic pattern gives rise to a highly reproducible Surface-Enhanced Raman Scattering (SERS) enhancement factor over the centimeter scale (std. dev. ∼10% over 0.25 cm2). The authors also discuss the application of a static elec. field for modulating the BCP host morphol. The elec. field induces an alignment of Au-NP clusters into ordered linear chains, exhibiting a stronger SERS activity, but reduced SERS spatial reproducibility.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXjtFCjtL4%253D&md5=8fcc715fb235afd2285a3e16f07bf63d
  8. 8
    Le Ru, E. C.; Etchegoin, P. G.; Grand, J.; Félidj, N.; Aubard, J.; Lévi, G.; Hohenau, A.; Krenn, J. R. Surface Enhanced Raman Spectroscopy on Nanolithography-Prepared Substrates. Curr. Appl. Phys. 2008, 8, 467– 470,  DOI: 10.1016/j.cap.2007.10.073
    Google Scholar
    There is no corresponding record for this reference.
  9. 9
    Das, G.; Mecarini, F.; Gentile, F.; De Angelis, F.; Mohan Kumar, M.; Candeloro, P.; Liberale, C.; Cuda, G.; Di Fabrizio, E. Nano-patterned SERS substrate: Application for protein analysis vs. temperature. Biosens. Bioelectron. 2009, 24, 1693– 1699,  DOI: 10.1016/j.bios.2008.08.050
    Google Scholar
    9
    Nano-patterned SERS substrate: application for protein analysis vs. temperature
    Das, Gobind; Mecarini, Federico; Gentile, Francesco; De Angelis, Francesco; Mohan, Kumar H. G.; Candeloro, Patrizio; Liberale, Carlo; Cuda, Giovanni; Di Fabrizio, Enzo
    Biosensors & Bioelectronics (2009), 24 (6), 1693-1699CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)
    The authors have illustrated the fabrication of nano-structures as a surface enhanced Raman scattering (SERS) substrate using electro-plating and electron-beam lithog. techniques to obtain an array of gold nanograin-aggregate structures of diam. ranging between 80 and 100 nm with interstitial gap of 10-30 nm. The nanostructure based SERS substrate permits us to have better control and reproducibility on generation of plasmon polaritons. The calcn. shows the possible detection of myoglobin concn. down to attomole. This SERS substrate is used to investigate the structural changes of different proteins; lysozyme, RNase-B, bovine serum albumin and myoglobin in the temp. range between -65° and 90°. The in-depth anal. even for small conformational changes is performed using 2D Raman correlation anal. and difference Raman anal. to gain straightforward understanding of proteins undergoing thermodynamical perturbation.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXltV2rtLg%253D&md5=dc743fef86e2e2bc950392ef00e70adb
  10. 10
    Reincke, F.; Hickey, S. G.; Kegel, W. K.; Vanmaekelbergh, D. Spontaneous Assembly of a Monolayer of Charged Gold Nanocrystals at the Water/Oil Interface. Angew. Chem., Int. Ed. Engl. 2004, 43, 458– 462,  DOI: 10.1002/anie.200352339
    Google Scholar
    10
    Spontaneous assembly of a monolayer of charged gold nanocrystals at the water/oil interface
    Reincke Francois; Hickey Stephen G; Kegel Willem K; Vanmaekelbergh Daniel
    Angewandte Chemie (International ed. in English) (2004), 43 (4), 458-62 ISSN:1433-7851.
    There is no expanded citation for this reference.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD2c%252FntFSjtQ%253D%253D&md5=d6405530ff37d812f58f879f432d5816
  11. 11
    Pienpinijtham, P.; Han, X. X.; Ekgasit, S.; Ozaki, Y. An Ionic Surfactant-Mediated Langmuir – Blodgett Method to Construct Gold Nanoparticle Films for Surface-Enhanced Raman Scattering. Phys. Chem. Chem. Phys. 2012, 14, 10132– 10139,  DOI: 10.1039/c2cp41419h
    Google Scholar
    11
    An ionic surfactant-mediated Langmuir-Blodgett method to construct gold nanoparticle films for surface-enhanced Raman scattering
    Pienpinijtham, Prompong; Han, Xiao Xia; Ekgasit, Sanong; Ozaki, Yukihiro
    Physical Chemistry Chemical Physics (2012), 14 (29), 10132-10139CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    A gold nanoparticle film for surface-enhanced Raman scattering (SERS) was successfully constructed by an ionic surfactant-mediated Langmuir-Blodgett (LB) method. The gold film was formed by adding ethanol to a gold colloid/hexane mixt. in the presence of dodecyltrimethylammonium bromide (DTAB). Consequently, gold nanoparticles (AuNPs) assembled at the water/hexane interface due to the decrease in surface charge d. of AuNPs. Since DTAB binds the gold surface by a Coulombic force, rather than a chem. bonding, it is easily replaced by target mols. for SERS purposes. The SERS enhancement factor of the 80 nm gold nanoparticle film was approx. 1.2 × 106 using crystal violet (CV) as a Raman dye. The SERS signal from the proposed DTAB-mediated film was approx. 10 times higher than that from the octanethiol-modified gold film, while the reproducibility and stability of this film compared to an octanethiol-modified film were similar. This method can also be applied to other metal nanostructures to fabricate metal films for use as a sensitive SERS substrate with a higher enhancement factor.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XpvVarur4%253D&md5=9f60f2ac2a72dc6dc22d149e152cb3d0
  12. 12
    Guo, Q.; Xu, M.; Yuan, Y.; Gu, R.; Yao, J. Self-Assembled Large-Scale Monolayer of Au Nanoparticles at the Air/Water Interface Used as a SERS Substrate. Langmuir 2016, 32, 4530– 4537,  DOI: 10.1021/acs.langmuir.5b04393
    Google Scholar
    12
    Self-Assembled Large-Scale Monolayer of Au Nanoparticles at the Air/Water Interface Used as a SERS Substrate
    Guo, Qinghua; Xu, Minmin; Yuan, Yaxian; Gu, Renao; Yao, Jianlin
    Langmuir (2016), 32 (18), 4530-4537CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    A facial approach for fabricating a monolayer film of Au nanoparticles is reported. Using the surfactant polyvinylpyrrolidone (PVP), a large-scale monolayer film of well-ordered, uniform-sized Au nanoparticles was fabricated at the air/water interface. The film exhibited a two-dimensional (2D) hcp. (HCP) structure having interparticle gaps smaller than 2 nm. These gaps generated numerous uniform "hot spots" for surface-enhanced Raman scattering (SERS) activity. The as-prepd. monolayer film could be transferred to a solid substrate for use as a suitable SERS substrate with high activity, high uniformity, and high stability. The low spot-to-spot and substrate-to-substrate variations of intensity ( < 10%), the large surface enhancement factor (∼106), and the high stability (∼45 days) make the substrate suitable for SERS measurements. Transfer of the monolayer film onto a glassy carbon electrode produced an Au electrode with clean, well-defined nanostructure suitable for electrochem. SERS measurements. The adsorption process of ionic liqs. on the electrode with the monolayer film is similar to that on bulk metal electrodes. The present strategy provides an effective way for self-assembly of Au nanoparticles into well-defined nanostructures that may form optimal reproducible SERS substrates for quant. anal. It also provides an electrode with clean, well-defined nanostructure for electrochem. investigations.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XmsVKktLc%253D&md5=0c961ff8829e4288cd4b00eeb0e7e3e6
  13. 13
    Liu, D.; Li, C.; Zhou, F.; Zhang, T.; Liu, G.; Cai, W.; Li, Y. Capillary Gradient-Induced Self-Assembly of Periodic Au Spherical Nanoparticle Arrays on an Ultralarge Scale via a Bisolvent System at Air/Water Interface. Adv. Mater. Interfaces 2017, 4, 1600976,  DOI: 10.1002/admi.201600976
    Google Scholar
    There is no corresponding record for this reference.
  14. 14
    Liu, S.; Zhu, T.; Hu, R.; Liu, Z. Evaporation-Induced Self-Assembly of Gold Nanoparticles into a Highly Organized Two-Dimensional Array. Phys. Chem. Chem. Phys. 2002, 4, 6059– 6062,  DOI: 10.1039/b208520h
    Google Scholar
    14
    Evaporation-induced self-assembly of gold nanoparticles into a highly organized two-dimensional array
    Liu, Shantang; Zhu, Tao; Hu, Ruisheng; Liu, Zhongfan
    Physical Chemistry Chemical Physics (2002), 4 (24), 6059-6062CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    This paper provides a convenient and simple method for fabricating a self-organized two-dimensional (2D) array of gold nanoparticles on a silicon substrate. The silicon substrate, modified with an aminopropyltriethoxysilane (APTES) monolayer, was first exposed to a gold colloidal suspension to deposit the gold particles and form a submonolayer of gold nanoparticles. This was followed by treatment with an alkanethiol soln., and then this randomly scattered submonolayer of nanosized gold particles on the silicon substrate was organized into small patches of 2D nanoparticle aggregates. Finally an alc. solvent was used to drive these small patches of gold nanoparticle aggregates to self-organize together and form continuous ordered arrays on the silicon surface. The SEM images of the samples show that ordered two-dimensional arrays of gold nanoparticles are formed over a very large area and that the nanoparticles are highly organized and formed hexagonally closed packed structured arrays. This highly organized structure of gold nanoparticles can be reproduced over a large area by these effective procedures. Therefore, it is believed such procedures hold promise as an advanced new approach to construct ordered mesoscopic structural materials or for the controlled self-assembly of nanoparticles and could provide the possibility of detecting the collective phys. properties of the ensemble.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XptFWmur4%253D&md5=ad20cf251e8da4b5348001a445931f1a
  15. 15
    Yang, G.; Nanda, J.; Wang, B.; Chen, G.; Hallinan, D. T., Jr. Self-Assembly of Large Gold nanoparticles for Surface-Enhanced Raman Spectroscopy. ACS Appl. Mater. Interfaces 2017, 9, 13457– 13470,  DOI: 10.1021/acsami.7b01121
    Google Scholar
    15
    Self-Assembly of Large Gold Nanoparticles for Surface-Enhanced Raman Spectroscopy
    Yang, Guang; Nanda, Jagjit; Wang, Boya; Chen, Gang; Hallinan, Daniel T.
    ACS Applied Materials & Interfaces (2017), 9 (15), 13457-13470CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    Performance of portable technologies from mobile phones to elec. vehicles is currently limited by the energy d. and lifetime of lithium batteries. Expanding the limits of battery technol. requires in situ detection of trace components at electrode-electrolyte interphases. Surface-enhance Raman spectroscopy could satisfy this need if a robust and reproducible substrate were available. Gold nanoparticles (Au NPs) larger than 20 nm diam. are expected to greatly enhance Raman intensity if they can be assembled into ordered monolayers. A three-phase self-assembly method is presented that successfully results in ordered Au NP monolayers for particle diams. ranging from 13 to 90 nm. The monolayer structure and Raman enhancement factors (EFs) are reported for a model analyte, rhodamine, as well as the best performing polymer electrolyte salt, lithium bis(trifluoromethane)sulfonimide. Exptl. EFs for the most part correlate with predictions based on monolayer geometry and with numerical simulations that identify local electromagnetic field enhancements. The EFs for the best performing Au NP monolayer are between 106 and 108 and give quant. signal response when analyte concn. is changed.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXkslKms7c%253D&md5=7a04ebae025331db6a69e980367a19ab
  16. 16
    Israelachvili, J. N.; Intermolecular and Surface Forces, 3rd ed.; Academic Press, 2011.
    Google Scholar
    There is no corresponding record for this reference.
  17. 17
    Njoki, P. N.; Lim, I. S.; Mott, D.; Park, H.; Khan, B.; Mishra, S.; Sujakumar, R.; Luo, J.; Zhong, C. Size Correlation of Optical and Spectroscopic Properties for Gold Nanoparticles. J. Phys. Chem. C 2007, 111, 14664– 14669,  DOI: 10.1021/jp074902z
    Google Scholar
    17
    Size Correlation of Optical and Spectroscopic Properties for Gold Nanoparticles
    Njoki, Peter N.; Lim, I-Im S.; Mott, Derrick; Park, Hye-Young; Khan, Bilal; Mishra, Suprav; Sujakumar, Ravishanker; Luo, Jin; Zhong, Chuan-Jian
    Journal of Physical Chemistry C (2007), 111 (40), 14664-14669CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    While the optical and spectroscopic properties of Au nanoparticles are widely used for chem., bioanal., and biomedical applications, the study of the size correlation with these properties for nanoparticles in solns. is rather limited. This paper describes the results of a systematic study of such a correlation for Au nanoparticles with diams. ranging from 10 to 100 nm in aq. solns. The high monodispersity of these nanoparticles permitted a meaningful correlation of the particle size with the surface plasmon (SP) resonance band properties and the surface-enhanced Raman scattering (SERS) spectroscopic properties. This correlation is compared to the results from the simulation based on Mie theory. The close agreement between the exptl. and the theor. results provides insight into the validity of detg. the wavelength of the SP resonance band as a measure of the particle size. The size correlation with the SERS intensity from the adsorption of 4-mercaptobenzoic acid on the nanoparticles in aq. solns. reveals the existence of a crit. size of the nanoparticles in the soln. beyond which the particle-particle interaction is operative and responsible for the SERS effect. These findings serve as the basis of size correlations for exploiting the optical and spectroscopic properties of Au nanoparticles of different sizes in aq. solns. in anal. or bioanal. applications.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXhtVChs7zI&md5=7127c1d91b6678f569d8066fced8017e
  18. 18
    Zhang, P.; Li, Y.; Wang, D.; Xia, H. High–Yield Production of Uniform Gold Nanoparticles with Sizes from 31 to 577 nm via One-Pot Seeded Growth and Size-Dependent SERS Property. Part. Part. Syst. Charact. 2016, 33, 924– 932,  DOI: 10.1002/ppsc.201600188
    Google Scholar
    18
    High-Yield Production of Uniform Gold Nanoparticles with Sizes from 31 to 577 nm via One-Pot Seeded Growth and Size-Dependent SERS Property
    Zhang, Peina; Li, Yijing; Wang, Dayang; Xia, Haibing
    Particle & Particle Systems Characterization (2016), 33 (12), 924-932CODEN: PPCHEZ; ISSN:1521-4117. (Wiley-VCH Verlag GmbH & Co. KGaA)
    In this work, uniform, quasi-spherical gold nanoparticles (Au NPs) with sizes of 31-577 nm are prepd. via one-pot seeded growth with the aid of tris-base (TB). Distinct from the seeded growth methods available in literature, the present method can be simply implemented by subsequently adding the aq. dispersion of the 17 nm Au-NP seeds and the aq. soln. of HAuCl4 into the boiling aq. TB soln. It is found that at the optimal pH range, the sizes of the final Au NPs and their concns. are simply controlled by either the particle no. of the Au seed dispersion or the concn. of the HAuCl4 soln., while the latter enables us to produce large Au NPs at very high concn. Moreover, as-prepd. Au NPs of various sizes are coated on glass substrates to test their surface-enhanced Raman scattering (SERS) activities by using 4-aminothiophenol (4-ATP) mols. as probes, which exhibit "volcano type" dependence on the Au NP sizes at fixed excitation wavelength. Furthermore, the Au NPs with sizes of ≈97 and 408 nm exhibit the largest SERS enhancement at the excitation wavelength of 633 and 785 nm, resp.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVOls7jK&md5=12305f7bd132355fb7ac915ecb649860
  19. 19
    Park, Y. K.; Yoo, S. H.; Park, S. Assembly of Highly Ordered Nanoparticle Monolayers at a Water/Hexane Interface. Langmuir 2007, 23, 10505– 10510,  DOI: 10.1021/la701445a
    Google Scholar
    19
    Assembly of Highly Ordered Nanoparticle Monolayers at a Water/Hexane Interface
    Park, Yong-Kyun; Yoo, Sang-Hoon; Park, Sungho
    Langmuir (2007), 23 (21), 10505-10510CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    This paper reports a methodol. for prepg. ordering hydrophilic metal nanoparticles into close-packed 2-dimensional arrays at a hexane-water interface with alkanethiol in the hexane layer. The destabilization of metal nanoparticles by the addn. of alc. caused the nanoparticles to adsorb to an interface where the surface of entrapped Au nanoparticle was in situ coated with the long-chain alkanethiols present in a hexane layer. The adsorption of alkanethiol to the nanoparticle surface caused the conversion of the electrostatic repulsive force to a van der Waals interaction, which is a key feature in forming highly ordered close-packed nanoparticle arrays.
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  20. 20
    Kim, B.; Tripp, S. L.; Wei, A. Self-Organization of Large Gold Nanoparticle Arrays. J. Am. Chem. Soc. 2001, 123, 7955– 7956,  DOI: 10.1021/ja0160344
    Google Scholar
    20
    Self-organization of large gold nanoparticle arrays
    Kim, Beomseok; Tripp, Steven L.; Wei, Alexander
    Journal of the American Chemical Society (2001), 123 (32), 7955-7956CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Conditions are described that enable large (16-170 nm) Au particles to self-organize at an air-water interface into monoparticulate films which can be subsequently transferred onto substrates as 2D hcp. arrays. The surfactant chosen was resorcinarene tetrathiol which is ideal for promoting the formation of the arrays with periodicities >170 nm. The self-assembly of large Au particles was achieved with structural precision and has excellent potential for the fabrication of nanostructured films with tunable optical and optoelectronic properties. The large Au nanoparticle arrays are esp. promising as substrates for surface-enhanced Raman scattering (SERS).
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  21. 21
    Ishida, T.; Tachikiri, Y.; Sako, T.; Takahashi, Y.; Yamada, S. Structural Characterization and Plasmonic Properties of Two-Dimensional Arrays of Hydrophobic Large Gold Nanoparticles Fabricated by Langmuir-Blodgett Technique. Appl. Surf. Sci. 2017, 404, 350– 356,  DOI: 10.1016/j.apsusc.2017.01.304
    Google Scholar
    21
    Structural characterization and plasmonic properties of two-dimensional arrays of hydrophobic large gold nanoparticles fabricated by Langmuir-Blodgett technique
    Ishida, Takuya; Tachikiri, Yuki; Sako, Takayuki; Takahashi, Yukina; Yamada, Sunao
    Applied Surface Science (2017), 404 (), 350-356CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
    The authors have succeeded in fabricating two-dimensional (2D) arrays of larger gold nanoparticles (AuNPs) (diams. 17, 28, and 48 nm) by Langmuir-Blodgett (LB) method. Although the particle size of AuNPs is one of the most important factors to control the optical properties of 2D arrays, there have been reported only the size of .ltorsim.20 nm. This is a first report on the bottom-up fabrication of 2D arrays consisting of hydrophobic AuNP with the diam. of ∼50 nm, of which the size is expected to obtain max. near-field effects. Octadecylthiolate-capped AuNPs (ODT-AuNPs) which were prepd. by the authors' method could be re-dispersed in chloroform even after drying completely, realizing the spreading of the colloidal chloroform soln. onto the water surface. Accordingly, densely-packed 2D LB films of ODT-AuNPs could be fabricated on an indium-tin-oxide substrate, when water as the subphase and polyethylene glycol (PEG) as an amphiphilic agent were used. PEG played an important role to form a densely packed film uniformly due to increasing affinity between hydrophobic AuNP and water. Absorption spectra of the films revealed that the resonance wavelengths of plasmon oscillation through interparticle plasmon coupling were clearly correlated with the particle sizes rather than deposition densities.
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  22. 22
    Wang, H.; Levin, C. S.; Halas, N. J. Nanosphere Arrays with Controlled Sub-10-Nm Gaps as Surface-Enhanced Raman Spectroscopy Substrates. J. Am. Chem. Soc. 2005, 127, 14992– 14993,  DOI: 10.1021/ja055633y
    Google Scholar
    22
    Nanosphere Arrays with Controlled Sub-10-nm Gaps as Surface-Enhanced Raman Spectroscopy Substrates
    Wang, Hui; Levin, Carly J.; Halas, Naomi J.
    Journal of the American Chemical Society (2005), 127 (43), 14992-14993CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    We demonstrate a convenient and cost-effective chem. approach for fabricating highly ordered Au nanoparticle arrays with sub-10-nm interparticle gaps. Near-field enhancements inside the interparticle gaps create uniform periodic arrays of well-defined "hot spots" exploitable for large surface-enhanced Raman spectroscopy (SERS) enhancements. A cetyltrimethylammonium bromide (CTAB) bilayer surrounding each individual nanoparticle upon array crystn. is responsible for this periodic gap structure; displacement of the CTAB by smaller thiolated mols. does not affect the structural integrity of the arrays. As SERS substrates, the as-fabricated Au nanoparticle arrays exhibit high SERS sensitivity, long-term stability, and consistent reproducibility.
    >> More from SciFinder ®
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  23. 23
    Wei, A.; Kim, B.; Pusztay, S. V.; Tripp, S. L.; Balasubramanian, R. Resorcinarene-Encapsulated Nanoparticles Building Blocks Self-Assembled Nanostructures. J. Inclusion Phenom. 2001, 41. DOI:  DOI: 10.1023/A:1014472212238
    Google Scholar
    There is no corresponding record for this reference.
  24. 24
    Smith, S. R.; Lipkowski, J. Guided Assembly of Two-Dimensional Arrays of Gold Nanoparticles on a Polycrystalline Gold Electrode for Electrochemical Surface- Enhanced Raman Spectroscopy. J. Phys. Chem. C 2018, 122, 7303– 7311,  DOI: 10.1021/acs.jpcc.8b01309
    Google Scholar
    24
    Guided Assembly of Two-Dimensional Arrays of Gold Nanoparticles on a Polycrystalline Gold Electrode for Electrochemical Surface-Enhanced Raman Spectroscopy
    Smith, Scott R.; Lipkowski, Jacek
    Journal of Physical Chemistry C (2018), 122 (13), 7303-7311CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Development of a reproducible two-dimensional array of gold nanoparticles (AuNPs) through a guided assembly approach and sequentially using an electrochem. cleaning procedure to remove all capping ligands and surface contaminants for studying gluconate, a weak Raman scatterer, with electrochem. surface-enhanced Raman spectroscopy (SERS) is discussed. Here, a unique use of shell-isolated nanoparticles (NPs) is presented by employing a thin-cell configuration during NP deposition to obtain a highly reproducible monolayer of AuNPs with spacing by 2× the SiO2 shell thickness. Upon SiO2 dissoln. and electrochem. cleaning, a well-ordered arrangement of bare AuNPs was achieved. The SERS active electrode modified with NP arrays was used for the characterization of gluconate adsorption. Enhanced spot-to-spot reproducibility of the SERS signal was achieved, allowing for significant redn. in the acquisition time needed for recording SERS spectra and investigation of gluconate adsorption on gold surfaces at short times. The results collected suggest that gluconate has undergone some electrooxidn. but remains well-hydrated in the interfacial region.
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  25. 25
    Shibamoto, K.; Yasumuro, S.; Horiuchi, K.; Teraoka, T.; Fujita, T. Study of Two-dimensional Highly-ordering of Gold Nanoparticles for an Optical Sensor Using Surface Plasmon Excitation as an Assistance Effect. Bunseki Kagaku 2014, 63, 293– 298,  DOI: 10.2116/bunsekikagaku.63.293
    Google Scholar
    25
    Study of two-dimensional highly-ordering of gold nanoparticles for an optical sensor using surface plasmon excitation as an assistance effect
    Shibamoto, Kohei; Yasumuro, Syunsuke; Horiuchi, Kentaro; Teraoka, Takuma; Fujita, Takashi
    Bunseki Kagaku (2014), 63 (4), 293-298CODEN: BNSKAK; ISSN:0525-1931. (Nippon Bunseki Kagakkai)
    The authors succeeded to fabricate a two-dimensional array of gold nanoparticles with high-ordering by using the surface plasmon excitation of gold nanoparticles for enhancing the repulsive force and controlling the aggregation through the process of fabrication. From SEM observations and spectroscopic measurements, we evaluated the order of the two-dimensional array of gold nanoparticles while taking account of particle isolation. Moreover, the high-ordering of the two-dimensional array provides higher sensitivity and higher reproducibility of Raman measurements. From these results, it is expected that the fabricated two-dimensional array of gold nanoparticles will lead to applications for a mol. sensor.
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  26. 26
    Shibamoto, K.; Kitajima, M.; Mohammad, K. H.; Patent, K. I. Fabrication of single layer array structure of surface unmodified metal nanoparticles. JP 4900550 B2, 2012.
    Google Scholar
    There is no corresponding record for this reference.
  27. 27
    Hentschel, M.; Dregely, D.; Vogelgesang, R.; Giessen, H.; Liu, N. Plasmonic Oligomers: The Role of Individual Particles in Collective Behavior. ACS Nano 2011, 5, 2042– 2050,  DOI: 10.1021/nn103172t
    Google Scholar
    27
    Plasmonic Oligomers: The Role of Individual Particles in Collective Behavior
    Hentschel, Mario; Dregely, Daniel; Vogelgesang, Ralf; Giessen, Harald; Liu, Na
    ACS Nano (2011), 5 (3), 2042-2050CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    A comprehensive exptl. study is presented of the optical properties of plasmonic oligomers. Both the constitution and configuration of plasmonic oligomers have a large influence on their resonant behavior, which draws a compelling analogy to mol. theory in chem. To elucidate the constitution influence, the size of individual nanoparticles were varied and the role identified of the target nanoparticle from the spectral change. To illustrate the configuration influence, the positions and nos. of nanoparticles in a plasmonic oligomer was varied. A large spectral red shift at the transition from displaced nanoparticles to touching ones was demonstrate exptl. The oligomeric design strategy opens up a rich pathway for the implementation of optimized optical properties into complex plasmonic nanostructures for specific applications.
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  28. 28
    Kneipp, K.; Kneipp, H.; Itzkan, I.; Dasari, R. R.; Feld, M. S. Single Molecule Detection Using near Infrared Surface-Enhanced Raman Scattering. Single Molecule Spectroscopy; Series in Chemical Physics; Springer, 2001; pp 144– 160.
    Google Scholar
    There is no corresponding record for this reference.
  29. 29
    Jiang, J. D.; Burstein, E.; Kobayashi, H. Resonant Raman Scattering by Crystal-Violet Molecules Adsorbed on a Smooth Gold Surface: Evidence for a Charge-Transfer Excitation. Phys. Rev. Lett. 1986, 57, 1793– 1796,  DOI: 10.1103/PhysRevLett.57.1793
    Google Scholar
    29
    Resonant Raman scattering by crystal-violet molecules adsorbed on a smooth gold surface: evidence for a charge-transfer excitation
    Jiang, J. D.; Burstein, E.; Kobayashi, H.
    Physical Review Letters (1986), 57 (14), 1793-6CODEN: PRLTAO; ISSN:0031-9007.
    Measurements are reported of excitation-profile spectra for Raman scattering from the central-C breathing mode of crystal violet adsorbed on a smooth Au surface. For polarization configurations that involve the xx (or yy) component of the Raman tensor, the spectra exhibit a resonance peak corresponding to the 1st singlet π-π* electronic excitation of adsorbed crystal-violet ions. The spectrum for the zz component does not exhibit this feature, but rather exhibits a steadily increasing scattering intensity with wavelength, that is attributed to an intermol. charge-transfer electronic excitation.
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  30. 30
    Cañamares, M. V.; Chenal, C.; Birke, R. L.; Lombardi, J. R. DFT, SERS, and Single-Molecule SERS of Crystal Violet. J. Phys. Chem. C 2008, 112, 20295– 20300,  DOI: 10.1021/jp807807j
    Google Scholar
    There is no corresponding record for this reference.
  31. 31
    Shibamoto, K.; Sakata, K.; Nagoshi, K.; Korenaga, T. Laser Desorption Ionization Mass Spectrometry by Using Surface Plasmon Excitation on Gold Nanoparticle. J. Phys. Chem. C 2009, 113, 17774– 17779,  DOI: 10.1021/jp9020432
    Google Scholar
    31
    Laser Desorption Ionization Mass Spectrometry by Using Surface Plasmon Excitation on Gold Nanoparticle
    Shibamoto, K.; Sakata, K.; Nagoshi, K.; Korenaga, T.
    Journal of Physical Chemistry C (2009), 113 (41), 17774-17779CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    The authors show development of a laser desorption/ionization (LDI) method with ultrahigh sensitivity by adding Au nanoparticles with a diam. of several tens of nanometers into a sample soln. The authors succeeded in detection of an ultratrace amt. of sample mols., which is less than several hundred zeptomoles. Probably the charge interaction based on surface plasmon (SP) excitation is very effective for ultrahigh sensitivity in LDI method.
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  32. 32
    Vinod, M.; Gopchandran, K. G. Au, Ag and Au:Ag Colloidal Nanoparticles Synthesized by Pulsed Laser Ablation as SERS Substrates. Prog. Nat. Sci.: Mater. Int. 2014, 24, 569– 578,  DOI: 10.1016/j.pnsc.2014.10.003
    Google Scholar
    32
    Au, Ag and Au:Ag colloidal nanoparticles synthesized by pulsed laser ablation as SERS substrates
    Vinod, M.; Gopchandran, K. G.
    Progress in Natural Science: Materials International (2014), 24 (6), 569-578CODEN: PNSMBB ISSN:. (Elsevier B.V.)
    CP colloidal suspensions of gold and silver nanoparticles were synthesized using pulsed laser ablation. The dependence of laser fluence on the surface plasmon characteristics of the nanoparticles was investigated. Au:Ag colloidal suspensions were prepd. by mixing highly monodisperse Au and Ag nanocolloids. The plasmon band of these mixts. was found to be highly sensitive to Au:Ag concn. ratio and wavelength of the laser beam used in the ablation process. The Au:Ag mixt. consists of almost spherical shaped nanostructures with a tendency to join with adjacent ones. The surface enhanced Raman scattering activity of the Au, Ag and Au:Ag colloidal suspensions was tested using crystal violet as probe mols. Enhancement in Raman signal obtained with Au:Ag substrates was found to be promising and strongly depends on its plasmon characteristics.
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  33. 33
    Lin, S.; Lin, X.; Song, X.; Han, S.; Wang, L.; Hasi, W. Fabrication of Flexible Paper - Based Surface - Enhanced Raman Scattering Substrate from Au Nanocubes Monolayer for Trace Detection of Crystal Violet on Shell. J. Raman Spectrosc. 2019, 50, 1074– 1084,  DOI: 10.1002/jrs.5620
    Google Scholar
    33
    Fabrication of flexible paper-based Surface-enhanced Raman scattering substrate from Au nanocubes monolayer for trace detection of crystal violet on shell
    Lin, Shuang; Lin, Xiang; Song, Xueying; Han, Siqingaowa; Wang, Li; Hasi, Wuliji
    Journal of Raman Spectroscopy (2019), 50 (8), 1074-1084CODEN: JRSPAF; ISSN:0377-0486. (John Wiley & Sons Ltd.)
    Surface-enhanced Raman scattering (SERS) substrate is the key to SERS technol. and it is still a basic focus to fabricate desirable SERS substrates offering multiple advantages of strong Raman enhancement and good reproducibility and portability. A flexible paper-based SERS substrate were fabricated involving the use of Au nanocubes (NCs) monolayer. Au NCs were generated with tunable size in the range of 24 to 63 nm through seed-mediated growth method. The effect of support on SERS properties of Au NCs-assembled monolayer was systemically explored. As a result, more excellent SERS performance could be obtained by assembling Au NCs on the filter paper. Besides, the influence of Au NCs' size on SERS-enhanced effect of paper-based substrate was also investigated. Our results clearly indicated that paper-based substrate with 39 nm Au NCs possessed the optimal SERS enhancement. This SERS substrate exhibited high sensitivity with enhancement factor (EF) up to 9.75 ×107 and demonstrated good uniformity and time stability. Furthermore, based on this superior paper-based SERS substrate with advantage of powerful sample extn. performance, the measurement of crystal violet (CV) on shell surface were successfully carried out with detection limit down to 2.17 × 10-7 M. And linear quantification were achieved in the range from 5 × 10-5 to 5 × 10-7 M. To sum up, the as-prepd. SERS substrate is applicable for on-site detection and anal. of CV on various shell surfaces.
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  34. 34
    Kneipp, K.; Kneipp, H.; Itzkan, I.; Dasari, R. R.; Feld, M. S. Ultrasensitive Chemical Analysis by Raman Spectroscopy. Chem. Rev. 1999, 99, 2957– 2976,  DOI: 10.1021/cr980133r
    Google Scholar
    34
    Ultrasensitive chemical analysis by Raman spectroscopy
    Kneipp, Katrin; Kneipp, Harald; Itzkan, Irving; Dasari, Ramachandra R.; Feld, Michael S.
    Chemical Reviews (Washington, D. C.) (1999), 99 (10), 2957-2975CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
    A review with 133 refs. is given on surface-enhanced Raman scattering, single-mol. Raman spectroscopy, crit. anal. and prospects of single-mol. Raman spectroscopy.
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  35. 35
    Shibamoto, K.; Katayama, K.; Sawada, T. Fundamental Processes of Surface Enhanced Raman Scattering Detected by Transient Reflecting Grating Spectroscopy. J. Photochem. Photobiol., A 2003, 158, 105– 110,  DOI: 10.1016/S1010-6030(03)00023-6
    Google Scholar
    35
    Fundamental processes of surface enhanced Raman scattering detected by transient reflecting grating spectroscopy
    Shibamoto, Kohei; Katayama, Kenji; Sawada, Tsuguo
    Journal of Photochemistry and Photobiology, A: Chemistry (2003), 158 (2-3), 105-110CODEN: JPPCEJ; ISSN:1010-6030. (Elsevier Science B.V.)
    Ultrafast charge transfer (CT) between gold and crystal violet (CV) mols. in relation with the surface enhanced Raman scattering (SERS) activation was investigated using the transient reflecting grating (TRG) spectroscopic method. A charge transfer between gold and crystal violet was obsd. only for the SERS-active substrate and it occurred within 200 fs. Since the adsorbed dyes had electronic overlap with the metal substrate at the point of central carbon, considering the difference of the Raman spectra between adsorbed and free dyes, it was suggested that the charge transfer occurred through the central carbon of crystal violet. Furthermore, it was shown that the surface morphol. of the substrates is in close correlation with the charge transfer process from its dependence on the prepn. method of substrates.
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  36. 36
    Shibamoto, K.; Katayama, K.; Sawada, T. Ultrafast Charge Transfer in Surface-Enhanced Raman Scattering (SERS) Processes Using Transient Reflecting Grating (TRG) Spectroscopy. Chem. Phys. Lett. 2007, 433, 385– 389,  DOI: 10.1016/j.cplett.2006.11.036
    Google Scholar
    36
    Ultrafast charge transfer in surface-enhanced Raman scattering (SERS) processes using transient reflecting grating (TRG) spectroscopy
    Shibamoto, Kohei; Katayama, Kenji; Sawada, Tsuguo
    Chemical Physics Letters (2007), 433 (4-6), 385-389CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
    Ultrafast dynamics was studied for photoexcited electrons between a SERS-active Au substrate and several kinds of adsorbed dyes by using TRG spectroscopy. A charge transfer (CT) within 200 fs between them was obsd. for a SERS-active sample and the no. of CT electrons had a strong correlation to both the relative adsorption energy states (AESs) of dyes and the enhancement factors of their SERS band. To increase the no. of CT electrons, the AESs should be closer to the excited energy state of Au. A larger no. of CT electrons are considered to make the enhancement of SERS band larger.
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  37. 37
    Deegan, R. D.; Bakajin, O.; Dupont, T. F.; Huber, G.; Nagel, S. R.; Witten, T. A. Capillary Flow as the Cause of Ring Stains from Dried Liquid Drops. Nature 1997, 389, 827– 829,  DOI: 10.1038/39827
    Google Scholar
    37
    Capillary flow as the cause of ring stains from dried liquid drops
    Deegan, Robert D.; Bakajin, Olgica; Dupont, Todd F.; Huber, Greg; Nagel, Sidney R.; Witten, Thomas A.
    Nature (London) (1997), 389 (6653), 827-829CODEN: NATUAS; ISSN:0028-0836. (Macmillan Magazines)
    When a spilled drop of coffee dries on a solid surface, it leaves a dense, ring-like deposit along the perimeter. The coffee - initially dispersed over the entire drop - becomes concd. into a tiny fraction of it. Such ring deposits are common wherever drops contg. dispersed solids evap. on a surface, and they influence processes such as printing, washing and coating. Ring deposits also provide a potential means to write or deposit a fine pattern onto a surface. Here we ascribe the characteristic pattern of the deposition to a form of capillary flow in which pinning of the contact line of the drying drop ensures that liq. evapg. from the edge is replenished by liq. from the interior. The resulting outward flow can carry virtually all the dispersed material to the edge. This mechanism predicts a distinctive power-law growth of the ring mass with time - a law independent of the particular substrate, carrier fluid or deposited solids. We have verified this law by microscopic observations of colloidal fluids.
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  1. Kohei Shibamoto, Takashi Fujita. Surface-Assisted Laser Desorption/Ionization Mass Spectrometry with a Two-Dimensional Au Nanoparticle Array for Soft Ionization. ACS Omega 2024, 9 (20) , 21822-21828. https://doi.org/10.1021/acsomega.3c08648
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  • Abstract

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    Figure 1

    Figure 1. (a) Optical microscopy image of the lateral meniscus image formed by the SW method at 0 min from the start. Dotted circle indicates a contact line. (b) Optical microscopy image of the contact line in the initial evaporation process (0, 45, 75, and 105 min from the start). (c) Reflection microscopy image of the contact line at t = 45 min.

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    Figure 2

    Figure 2. (a) SEM image at ×50 magnification of SW-substrate 1 on the Si wafer, which was prepared at a relative humidity of 60 ± 10% at 298 K. (b) SEM image at ×20,000 magnification of SW-substrate 1. (c) SEM image at ×20,000 magnification of SW-substrate 2, which was prepared at a relative humidity of 20 ± 5% at 298 K. These substrates were composed of spherical Au NPs (mean diameter: 60 nm). Corresponding FFT images and their brightness distribution are shown in the higher right and lower right, respectively.

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    Figure 3

    Figure 3. (a) SEM image at ×20,000 magnification of the OW-substrate on the Si wafer. (b) SEM image at ×20,000 magnification of the DD-substrate on Si wafer. These substrates were composed of spherical Au NPs (mean diameter: 60 nm). Corresponding FFT images and their brightness distribution are shown in the higher right and lower right, respectively.

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    Figure 4

    Figure 4. Vis–NIR Extinction spectra of (a) SW-substrate 1, (b) OW-substrate, and (c) DD-substrate. These substrates were on glass slides. The dotted line indicates vis–NIR absorption spectra of spherical Au NP (mean diameter: 60 nm) colloidal solution, which was used for the preparation of these substrates.

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    Figure 5

    Figure 5. (a) Raman spectra of CV adsorbed on SW-substrate 1 and (b) Raman spectra of CV crystals. 532 nm lines of Nd:YAG laser was employed as the excitation laser.

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    Figure 6

    Figure 6. Normalized peak intensities of bands at (a) 1179 cm–1, (b) 1380 cm–1, and (c) 1621 cm–1 versus packing rates of four substrates. The mean value was normalized to 1 (dotted line). These peak intensities were obtained from different 25 spots in these substrates. (d) RSDs of SERS intensities at 1621 cm–1 versus packing rates of four substrates. The dotted line indicates the systematic error obtained from a silicon single crystal (100).

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  • References

    This article references 37 other publications.

    1. 1
      Mayer, K. M.; Hafner, J. H. Localized Surface Plasmon Resonance Sensors. Chem. Rev. 2011, 111, 3828– 3857,  DOI: 10.1021/cr100313v
      1
      Localized surface plasmon resonance sensors
      Mayer, Kathryn M.; Hafner, Jason H.
      Chemical Reviews (Washington, DC, United States) (2011), 111 (6), 3828-3857CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. Topics include physics of localized surface plasmon resonance (LSPR); sensing with LSPR, effect of particle size, shape, and material; LSPR-based biol. and chem. sensors; technol. advances in LSPR sensing; maximizing the mol. detection sensitivity of LSPR; and future directions like mol. biol. or diagnostic tool application.
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    2. 2
      Jiang, N.; Zhuo, X.; Wang, J. Active Plasmonics: Principles, Structures, and Applications. Chem. Rev. 2018, 118, 3054– 3099,  DOI: 10.1021/acs.chemrev.7b00252
      2
      Active Plasmonics: Principles, Structures, and Applications
      Jiang, Nina; Zhuo, Xiaolu; Wang, Jianfang
      Chemical Reviews (Washington, DC, United States) (2018), 118 (6), 3054-3099CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review. Active plasmonics is a burgeoning and challenging subfield of plasmonics. It exploits the active control of surface plasmon resonance. In this review, a first-ever in-depth description of the theor. relationship between surface plasmon resonance and its affecting factors, which forms the basis for active plasmon control, will be presented. Three categories of active plasmonic structures, consisting of plasmonic structures in tunable dielec. surroundings, plasmonic structures with tunable gap distances, and self-tunable plasmonic structures, will be proposed in terms of the modulation mechanism. The recent advances and current challenges for these three categories of active plasmonic structures will be discussed in detail. The flourishing development of active plasmonic structures opens access to new application fields. A significant part of this review will be devoted to the applications of active plasmonic structures in plasmonic sensing, tunable surface-enhanced Raman scattering, active plasmonic components, and electrochromic smart windows. This review will be concluded with a section on the future challenges and prospects for active plasmonics.
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    3. 3
      Kleinman, S. L.; Frontiera, R. R.; Henry, A. I.; Dieringer, J. A.; Van Duyne, R. P. Creating, Characterizing, and Controlling Chemistry with SERS Hot Spots. Phys. Chem. Chem. Phys. 2013, 15, 21– 36,  DOI: 10.1039/c2cp42598j
      3
      Creating, characterizing, and controlling chemistry with SERS hot spots
      Kleinman, Samuel L.; Frontiera, Renee R.; Henry, Anne-Isabelle; Dieringer, Jon A.; Van Duyne, Richard P.
      Physical Chemistry Chemical Physics (2013), 15 (1), 21-36CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      A review. In this perspective the roles of hot spots in surface-enhanced Raman spectroscopy (SERS) are discussed. After giving background and defining the hot spot, the authors evaluate a variety of SERS substrates which often contain hot spots. The authors compare and discuss the differentiating properties of each substrate. The authors then provide a thorough anal. of the hot spot contribution to the obsd. SERS signal both in ensemble-averaged and single-mol. conditions. The authors also enumerate rules for detg. the SERS enhancement factor (EF) to clarify the use of this common metric. Finally, the authors present a forward-looking overview of applications and uses of hot spots for controlling chem. on the nanoscale. Although not exhaustive, this perspective is a review of some of the most interesting and promising methodologies for creating, controlling, and using hot spots for electromagnetic amplification.
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    4. 4
      Sharma, B.; Frontiera, R. R.; Henry, A. I.; Ringe, E.; Van Duyne, R. P. SERS: Materials, Applications, and the Future. Mater. Today 2012, 15, 16– 25,  DOI: 10.1016/S1369-7021(12)70017-2
      4
      SERS: Materials, applications, and the future
      Sharma, Bhavya; Frontiera, Renee R.; Henry, Anne-Isabelle; Ringe, Emilie; Van Duyne, Richard P.
      Materials Today (Oxford, United Kingdom) (2012), 15 (1-2), 16-25CODEN: MTOUAN; ISSN:1369-7021. (Elsevier Ltd.)
      A review. Surface enhanced Raman spectroscopy (SERS) is a powerful vibrational spectroscopy technique that allows for highly sensitive structural detection of low concn. analytes through the amplification of electromagnetic fields generated by the excitation of localized surface plasmons. SERS has progressed from studies of model systems on roughened electrodes to highly sophisticated studies, such as single mol. spectroscopy. We summarize the current state of knowledge concerning the mechanism of SERS and new substrate materials. We highlight recent applications of SERS including sensing, spectroelectrochem., single mol. SERS, and real-world applications. We also discuss contributions to the field from the Van Duyne group. This review concludes with a discussion of future directions for this field including biol. probing with UV-SERS, tip-enhanced Raman spectroscopy, and ultrafast SERS.
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    5. 5
      Huang, Z.; Zhang, A.; Zhang, Q.; Cui, D.; Nanomaterial-Based, S. E. R. S. Nanomaterial-Based SERS Sensing Technology for Biomedical Application. J. Mater. Chem. B 2019, 7, 3755– 3774,  DOI: 10.1039/C9TB00666D
      5
      Nanomaterial-based SERS sensing technology for biomedical application
      Huang, Zhicheng; Zhang, Amin; Zhang, Qian; Cui, Daxiang
      Journal of Materials Chemistry B: Materials for Biology and Medicine (2019), 7 (24), 3755-3774CODEN: JMCBDV; ISSN:2050-7518. (Royal Society of Chemistry)
      Over the past few years, nanomaterial-based surface-enhanced Raman scattering (SERS) detection has emerged as a new exciting field in which theor. and exptl. studies of the structure and function of nanomaterials have become a focus. The importance of different dimensional nanomaterials has begun to be recognized, esp. in the fundamental development of SERS sensing detection for biomedical application. Great advances have been and are being made in different dimensional nanomaterial-based SERS technol. with enormous prospects in clin. medicine applications. Herein we review some of the main advances in this field over the past few years, explore the application prospects, and discuss the concepts, issues, approaches and challenges, with the aim of stimulating broader interest in developing nanomaterial-based SERS sensing applications for medical theranostics.
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    6. 6
      Sackmann, M.; Materny, A. Surface Enhanced Raman Scattering (SERS) – A Quantitative Analytical Tool?. J. Raman Spectrosc. 2006, 37, 305– 310,  DOI: 10.1002/jrs.1443
      6
      Surface enhanced Raman scattering (SERS) - a quantitative analytical tool?
      Sackmann, M.; Materny, A.
      Journal of Raman Spectroscopy (2006), 37 (1-3), 305-310CODEN: JRSPAF; ISSN:0377-0486. (John Wiley & Sons Ltd.)
      Raman spectroscopy is a widely used anal. tool capable of providing valuable information about the chem. structure and compn. of mols. In order to detect substances also at a very low concn. levels, Surface Enhanced Raman Scattering (SERS) was introduced. The different amplification mechanisms result in extreme sensitivity, however, a quant. use of SERS appears to be problematic. Esp., when deploying silver sols as SERS substrates, the reproducibility of the signal intensities for a given substance concn. is questionable. Exptl. results of an investigation of this problem for low concns. of adenine are presented. Comparison with results obtained for different SERS substrates by other authors reveals clearly different dependencies. Only in a very limited concn. range reproducible and therefore quant. utilizable data could be obtained.
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    7. 7
      De Rosa, C.; Auriemma, F.; Diletto, C.; Di Girolamo, R.; Malafronte, A.; Morvillo, P.; Zito, T.; Rusciano, G.; Pesce, G.; Sasso, A. Toward hyperuniform disordered plasmonic nanostructures for reproducible surface-enhanced Raman spectroscopy. Phys. Chem. Chem. Phys. 2015, 17, 8061– 8069,  DOI: 10.1039/c4cp06024e
      7
      Toward hyperuniform disordered plasmonic nanostructures for reproducible surface-enhanced Raman spectroscopy
      De Rosa, C.; Auriemma, F.; Diletto, C.; Di Girolamo, R.; Malafronte, A.; Morvillo, P.; Zito, G.; Rusciano, G.; Pesce, G.; Sasso, A.
      Physical Chemistry Chemical Physics (2015), 17 (12), 8061-8069CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      The authors report on the self-assembling of clusters of Au-nanoparticles (Au-NPs) directed by the phase sepn. of poly(styrene)-b-poly(methylmethacrylate) (PS-b-PMMA) block-copolymer (BCP) on In Sn oxide coated glass, which induces the onset of vertical lamellar domains. After thermal evapn. of Au on BCP, Au-NPs of 4 nm are selectively included into PS-nanodomains by thermal annealing, and then clustered with large d. of hot spots (> 104 μm2) in a random 2-dimensional pattern. The resulting nanostructure exhibits near-hyperuniform long-range correlations. The consequent large degree of homogeneity of this isotropic plasmonic pattern gives rise to a highly reproducible Surface-Enhanced Raman Scattering (SERS) enhancement factor over the centimeter scale (std. dev. ∼10% over 0.25 cm2). The authors also discuss the application of a static elec. field for modulating the BCP host morphol. The elec. field induces an alignment of Au-NP clusters into ordered linear chains, exhibiting a stronger SERS activity, but reduced SERS spatial reproducibility.
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    8. 8
      Le Ru, E. C.; Etchegoin, P. G.; Grand, J.; Félidj, N.; Aubard, J.; Lévi, G.; Hohenau, A.; Krenn, J. R. Surface Enhanced Raman Spectroscopy on Nanolithography-Prepared Substrates. Curr. Appl. Phys. 2008, 8, 467– 470,  DOI: 10.1016/j.cap.2007.10.073
      There is no corresponding record for this reference.
    9. 9
      Das, G.; Mecarini, F.; Gentile, F.; De Angelis, F.; Mohan Kumar, M.; Candeloro, P.; Liberale, C.; Cuda, G.; Di Fabrizio, E. Nano-patterned SERS substrate: Application for protein analysis vs. temperature. Biosens. Bioelectron. 2009, 24, 1693– 1699,  DOI: 10.1016/j.bios.2008.08.050
      9
      Nano-patterned SERS substrate: application for protein analysis vs. temperature
      Das, Gobind; Mecarini, Federico; Gentile, Francesco; De Angelis, Francesco; Mohan, Kumar H. G.; Candeloro, Patrizio; Liberale, Carlo; Cuda, Giovanni; Di Fabrizio, Enzo
      Biosensors & Bioelectronics (2009), 24 (6), 1693-1699CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)
      The authors have illustrated the fabrication of nano-structures as a surface enhanced Raman scattering (SERS) substrate using electro-plating and electron-beam lithog. techniques to obtain an array of gold nanograin-aggregate structures of diam. ranging between 80 and 100 nm with interstitial gap of 10-30 nm. The nanostructure based SERS substrate permits us to have better control and reproducibility on generation of plasmon polaritons. The calcn. shows the possible detection of myoglobin concn. down to attomole. This SERS substrate is used to investigate the structural changes of different proteins; lysozyme, RNase-B, bovine serum albumin and myoglobin in the temp. range between -65° and 90°. The in-depth anal. even for small conformational changes is performed using 2D Raman correlation anal. and difference Raman anal. to gain straightforward understanding of proteins undergoing thermodynamical perturbation.
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    10. 10
      Reincke, F.; Hickey, S. G.; Kegel, W. K.; Vanmaekelbergh, D. Spontaneous Assembly of a Monolayer of Charged Gold Nanocrystals at the Water/Oil Interface. Angew. Chem., Int. Ed. Engl. 2004, 43, 458– 462,  DOI: 10.1002/anie.200352339
      10
      Spontaneous assembly of a monolayer of charged gold nanocrystals at the water/oil interface
      Reincke Francois; Hickey Stephen G; Kegel Willem K; Vanmaekelbergh Daniel
      Angewandte Chemie (International ed. in English) (2004), 43 (4), 458-62 ISSN:1433-7851.
      There is no expanded citation for this reference.
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    11. 11
      Pienpinijtham, P.; Han, X. X.; Ekgasit, S.; Ozaki, Y. An Ionic Surfactant-Mediated Langmuir – Blodgett Method to Construct Gold Nanoparticle Films for Surface-Enhanced Raman Scattering. Phys. Chem. Chem. Phys. 2012, 14, 10132– 10139,  DOI: 10.1039/c2cp41419h
      11
      An ionic surfactant-mediated Langmuir-Blodgett method to construct gold nanoparticle films for surface-enhanced Raman scattering
      Pienpinijtham, Prompong; Han, Xiao Xia; Ekgasit, Sanong; Ozaki, Yukihiro
      Physical Chemistry Chemical Physics (2012), 14 (29), 10132-10139CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      A gold nanoparticle film for surface-enhanced Raman scattering (SERS) was successfully constructed by an ionic surfactant-mediated Langmuir-Blodgett (LB) method. The gold film was formed by adding ethanol to a gold colloid/hexane mixt. in the presence of dodecyltrimethylammonium bromide (DTAB). Consequently, gold nanoparticles (AuNPs) assembled at the water/hexane interface due to the decrease in surface charge d. of AuNPs. Since DTAB binds the gold surface by a Coulombic force, rather than a chem. bonding, it is easily replaced by target mols. for SERS purposes. The SERS enhancement factor of the 80 nm gold nanoparticle film was approx. 1.2 × 106 using crystal violet (CV) as a Raman dye. The SERS signal from the proposed DTAB-mediated film was approx. 10 times higher than that from the octanethiol-modified gold film, while the reproducibility and stability of this film compared to an octanethiol-modified film were similar. This method can also be applied to other metal nanostructures to fabricate metal films for use as a sensitive SERS substrate with a higher enhancement factor.
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    12. 12
      Guo, Q.; Xu, M.; Yuan, Y.; Gu, R.; Yao, J. Self-Assembled Large-Scale Monolayer of Au Nanoparticles at the Air/Water Interface Used as a SERS Substrate. Langmuir 2016, 32, 4530– 4537,  DOI: 10.1021/acs.langmuir.5b04393
      12
      Self-Assembled Large-Scale Monolayer of Au Nanoparticles at the Air/Water Interface Used as a SERS Substrate
      Guo, Qinghua; Xu, Minmin; Yuan, Yaxian; Gu, Renao; Yao, Jianlin
      Langmuir (2016), 32 (18), 4530-4537CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      A facial approach for fabricating a monolayer film of Au nanoparticles is reported. Using the surfactant polyvinylpyrrolidone (PVP), a large-scale monolayer film of well-ordered, uniform-sized Au nanoparticles was fabricated at the air/water interface. The film exhibited a two-dimensional (2D) hcp. (HCP) structure having interparticle gaps smaller than 2 nm. These gaps generated numerous uniform "hot spots" for surface-enhanced Raman scattering (SERS) activity. The as-prepd. monolayer film could be transferred to a solid substrate for use as a suitable SERS substrate with high activity, high uniformity, and high stability. The low spot-to-spot and substrate-to-substrate variations of intensity ( < 10%), the large surface enhancement factor (∼106), and the high stability (∼45 days) make the substrate suitable for SERS measurements. Transfer of the monolayer film onto a glassy carbon electrode produced an Au electrode with clean, well-defined nanostructure suitable for electrochem. SERS measurements. The adsorption process of ionic liqs. on the electrode with the monolayer film is similar to that on bulk metal electrodes. The present strategy provides an effective way for self-assembly of Au nanoparticles into well-defined nanostructures that may form optimal reproducible SERS substrates for quant. anal. It also provides an electrode with clean, well-defined nanostructure for electrochem. investigations.
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    13. 13
      Liu, D.; Li, C.; Zhou, F.; Zhang, T.; Liu, G.; Cai, W.; Li, Y. Capillary Gradient-Induced Self-Assembly of Periodic Au Spherical Nanoparticle Arrays on an Ultralarge Scale via a Bisolvent System at Air/Water Interface. Adv. Mater. Interfaces 2017, 4, 1600976,  DOI: 10.1002/admi.201600976
      There is no corresponding record for this reference.
    14. 14
      Liu, S.; Zhu, T.; Hu, R.; Liu, Z. Evaporation-Induced Self-Assembly of Gold Nanoparticles into a Highly Organized Two-Dimensional Array. Phys. Chem. Chem. Phys. 2002, 4, 6059– 6062,  DOI: 10.1039/b208520h
      14
      Evaporation-induced self-assembly of gold nanoparticles into a highly organized two-dimensional array
      Liu, Shantang; Zhu, Tao; Hu, Ruisheng; Liu, Zhongfan
      Physical Chemistry Chemical Physics (2002), 4 (24), 6059-6062CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      This paper provides a convenient and simple method for fabricating a self-organized two-dimensional (2D) array of gold nanoparticles on a silicon substrate. The silicon substrate, modified with an aminopropyltriethoxysilane (APTES) monolayer, was first exposed to a gold colloidal suspension to deposit the gold particles and form a submonolayer of gold nanoparticles. This was followed by treatment with an alkanethiol soln., and then this randomly scattered submonolayer of nanosized gold particles on the silicon substrate was organized into small patches of 2D nanoparticle aggregates. Finally an alc. solvent was used to drive these small patches of gold nanoparticle aggregates to self-organize together and form continuous ordered arrays on the silicon surface. The SEM images of the samples show that ordered two-dimensional arrays of gold nanoparticles are formed over a very large area and that the nanoparticles are highly organized and formed hexagonally closed packed structured arrays. This highly organized structure of gold nanoparticles can be reproduced over a large area by these effective procedures. Therefore, it is believed such procedures hold promise as an advanced new approach to construct ordered mesoscopic structural materials or for the controlled self-assembly of nanoparticles and could provide the possibility of detecting the collective phys. properties of the ensemble.
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    15. 15
      Yang, G.; Nanda, J.; Wang, B.; Chen, G.; Hallinan, D. T., Jr. Self-Assembly of Large Gold nanoparticles for Surface-Enhanced Raman Spectroscopy. ACS Appl. Mater. Interfaces 2017, 9, 13457– 13470,  DOI: 10.1021/acsami.7b01121
      15
      Self-Assembly of Large Gold Nanoparticles for Surface-Enhanced Raman Spectroscopy
      Yang, Guang; Nanda, Jagjit; Wang, Boya; Chen, Gang; Hallinan, Daniel T.
      ACS Applied Materials & Interfaces (2017), 9 (15), 13457-13470CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Performance of portable technologies from mobile phones to elec. vehicles is currently limited by the energy d. and lifetime of lithium batteries. Expanding the limits of battery technol. requires in situ detection of trace components at electrode-electrolyte interphases. Surface-enhance Raman spectroscopy could satisfy this need if a robust and reproducible substrate were available. Gold nanoparticles (Au NPs) larger than 20 nm diam. are expected to greatly enhance Raman intensity if they can be assembled into ordered monolayers. A three-phase self-assembly method is presented that successfully results in ordered Au NP monolayers for particle diams. ranging from 13 to 90 nm. The monolayer structure and Raman enhancement factors (EFs) are reported for a model analyte, rhodamine, as well as the best performing polymer electrolyte salt, lithium bis(trifluoromethane)sulfonimide. Exptl. EFs for the most part correlate with predictions based on monolayer geometry and with numerical simulations that identify local electromagnetic field enhancements. The EFs for the best performing Au NP monolayer are between 106 and 108 and give quant. signal response when analyte concn. is changed.
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    16. 16
      Israelachvili, J. N.; Intermolecular and Surface Forces, 3rd ed.; Academic Press, 2011.
      There is no corresponding record for this reference.
    17. 17
      Njoki, P. N.; Lim, I. S.; Mott, D.; Park, H.; Khan, B.; Mishra, S.; Sujakumar, R.; Luo, J.; Zhong, C. Size Correlation of Optical and Spectroscopic Properties for Gold Nanoparticles. J. Phys. Chem. C 2007, 111, 14664– 14669,  DOI: 10.1021/jp074902z
      17
      Size Correlation of Optical and Spectroscopic Properties for Gold Nanoparticles
      Njoki, Peter N.; Lim, I-Im S.; Mott, Derrick; Park, Hye-Young; Khan, Bilal; Mishra, Suprav; Sujakumar, Ravishanker; Luo, Jin; Zhong, Chuan-Jian
      Journal of Physical Chemistry C (2007), 111 (40), 14664-14669CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      While the optical and spectroscopic properties of Au nanoparticles are widely used for chem., bioanal., and biomedical applications, the study of the size correlation with these properties for nanoparticles in solns. is rather limited. This paper describes the results of a systematic study of such a correlation for Au nanoparticles with diams. ranging from 10 to 100 nm in aq. solns. The high monodispersity of these nanoparticles permitted a meaningful correlation of the particle size with the surface plasmon (SP) resonance band properties and the surface-enhanced Raman scattering (SERS) spectroscopic properties. This correlation is compared to the results from the simulation based on Mie theory. The close agreement between the exptl. and the theor. results provides insight into the validity of detg. the wavelength of the SP resonance band as a measure of the particle size. The size correlation with the SERS intensity from the adsorption of 4-mercaptobenzoic acid on the nanoparticles in aq. solns. reveals the existence of a crit. size of the nanoparticles in the soln. beyond which the particle-particle interaction is operative and responsible for the SERS effect. These findings serve as the basis of size correlations for exploiting the optical and spectroscopic properties of Au nanoparticles of different sizes in aq. solns. in anal. or bioanal. applications.
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    18. 18
      Zhang, P.; Li, Y.; Wang, D.; Xia, H. High–Yield Production of Uniform Gold Nanoparticles with Sizes from 31 to 577 nm via One-Pot Seeded Growth and Size-Dependent SERS Property. Part. Part. Syst. Charact. 2016, 33, 924– 932,  DOI: 10.1002/ppsc.201600188
      18
      High-Yield Production of Uniform Gold Nanoparticles with Sizes from 31 to 577 nm via One-Pot Seeded Growth and Size-Dependent SERS Property
      Zhang, Peina; Li, Yijing; Wang, Dayang; Xia, Haibing
      Particle & Particle Systems Characterization (2016), 33 (12), 924-932CODEN: PPCHEZ; ISSN:1521-4117. (Wiley-VCH Verlag GmbH & Co. KGaA)
      In this work, uniform, quasi-spherical gold nanoparticles (Au NPs) with sizes of 31-577 nm are prepd. via one-pot seeded growth with the aid of tris-base (TB). Distinct from the seeded growth methods available in literature, the present method can be simply implemented by subsequently adding the aq. dispersion of the 17 nm Au-NP seeds and the aq. soln. of HAuCl4 into the boiling aq. TB soln. It is found that at the optimal pH range, the sizes of the final Au NPs and their concns. are simply controlled by either the particle no. of the Au seed dispersion or the concn. of the HAuCl4 soln., while the latter enables us to produce large Au NPs at very high concn. Moreover, as-prepd. Au NPs of various sizes are coated on glass substrates to test their surface-enhanced Raman scattering (SERS) activities by using 4-aminothiophenol (4-ATP) mols. as probes, which exhibit "volcano type" dependence on the Au NP sizes at fixed excitation wavelength. Furthermore, the Au NPs with sizes of ≈97 and 408 nm exhibit the largest SERS enhancement at the excitation wavelength of 633 and 785 nm, resp.
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    19. 19
      Park, Y. K.; Yoo, S. H.; Park, S. Assembly of Highly Ordered Nanoparticle Monolayers at a Water/Hexane Interface. Langmuir 2007, 23, 10505– 10510,  DOI: 10.1021/la701445a
      19
      Assembly of Highly Ordered Nanoparticle Monolayers at a Water/Hexane Interface
      Park, Yong-Kyun; Yoo, Sang-Hoon; Park, Sungho
      Langmuir (2007), 23 (21), 10505-10510CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      This paper reports a methodol. for prepg. ordering hydrophilic metal nanoparticles into close-packed 2-dimensional arrays at a hexane-water interface with alkanethiol in the hexane layer. The destabilization of metal nanoparticles by the addn. of alc. caused the nanoparticles to adsorb to an interface where the surface of entrapped Au nanoparticle was in situ coated with the long-chain alkanethiols present in a hexane layer. The adsorption of alkanethiol to the nanoparticle surface caused the conversion of the electrostatic repulsive force to a van der Waals interaction, which is a key feature in forming highly ordered close-packed nanoparticle arrays.
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    20. 20
      Kim, B.; Tripp, S. L.; Wei, A. Self-Organization of Large Gold Nanoparticle Arrays. J. Am. Chem. Soc. 2001, 123, 7955– 7956,  DOI: 10.1021/ja0160344
      20
      Self-organization of large gold nanoparticle arrays
      Kim, Beomseok; Tripp, Steven L.; Wei, Alexander
      Journal of the American Chemical Society (2001), 123 (32), 7955-7956CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Conditions are described that enable large (16-170 nm) Au particles to self-organize at an air-water interface into monoparticulate films which can be subsequently transferred onto substrates as 2D hcp. arrays. The surfactant chosen was resorcinarene tetrathiol which is ideal for promoting the formation of the arrays with periodicities >170 nm. The self-assembly of large Au particles was achieved with structural precision and has excellent potential for the fabrication of nanostructured films with tunable optical and optoelectronic properties. The large Au nanoparticle arrays are esp. promising as substrates for surface-enhanced Raman scattering (SERS).
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    21. 21
      Ishida, T.; Tachikiri, Y.; Sako, T.; Takahashi, Y.; Yamada, S. Structural Characterization and Plasmonic Properties of Two-Dimensional Arrays of Hydrophobic Large Gold Nanoparticles Fabricated by Langmuir-Blodgett Technique. Appl. Surf. Sci. 2017, 404, 350– 356,  DOI: 10.1016/j.apsusc.2017.01.304
      21
      Structural characterization and plasmonic properties of two-dimensional arrays of hydrophobic large gold nanoparticles fabricated by Langmuir-Blodgett technique
      Ishida, Takuya; Tachikiri, Yuki; Sako, Takayuki; Takahashi, Yukina; Yamada, Sunao
      Applied Surface Science (2017), 404 (), 350-356CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
      The authors have succeeded in fabricating two-dimensional (2D) arrays of larger gold nanoparticles (AuNPs) (diams. 17, 28, and 48 nm) by Langmuir-Blodgett (LB) method. Although the particle size of AuNPs is one of the most important factors to control the optical properties of 2D arrays, there have been reported only the size of .ltorsim.20 nm. This is a first report on the bottom-up fabrication of 2D arrays consisting of hydrophobic AuNP with the diam. of ∼50 nm, of which the size is expected to obtain max. near-field effects. Octadecylthiolate-capped AuNPs (ODT-AuNPs) which were prepd. by the authors' method could be re-dispersed in chloroform even after drying completely, realizing the spreading of the colloidal chloroform soln. onto the water surface. Accordingly, densely-packed 2D LB films of ODT-AuNPs could be fabricated on an indium-tin-oxide substrate, when water as the subphase and polyethylene glycol (PEG) as an amphiphilic agent were used. PEG played an important role to form a densely packed film uniformly due to increasing affinity between hydrophobic AuNP and water. Absorption spectra of the films revealed that the resonance wavelengths of plasmon oscillation through interparticle plasmon coupling were clearly correlated with the particle sizes rather than deposition densities.
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    22. 22
      Wang, H.; Levin, C. S.; Halas, N. J. Nanosphere Arrays with Controlled Sub-10-Nm Gaps as Surface-Enhanced Raman Spectroscopy Substrates. J. Am. Chem. Soc. 2005, 127, 14992– 14993,  DOI: 10.1021/ja055633y
      22
      Nanosphere Arrays with Controlled Sub-10-nm Gaps as Surface-Enhanced Raman Spectroscopy Substrates
      Wang, Hui; Levin, Carly J.; Halas, Naomi J.
      Journal of the American Chemical Society (2005), 127 (43), 14992-14993CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      We demonstrate a convenient and cost-effective chem. approach for fabricating highly ordered Au nanoparticle arrays with sub-10-nm interparticle gaps. Near-field enhancements inside the interparticle gaps create uniform periodic arrays of well-defined "hot spots" exploitable for large surface-enhanced Raman spectroscopy (SERS) enhancements. A cetyltrimethylammonium bromide (CTAB) bilayer surrounding each individual nanoparticle upon array crystn. is responsible for this periodic gap structure; displacement of the CTAB by smaller thiolated mols. does not affect the structural integrity of the arrays. As SERS substrates, the as-fabricated Au nanoparticle arrays exhibit high SERS sensitivity, long-term stability, and consistent reproducibility.
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    23. 23
      Wei, A.; Kim, B.; Pusztay, S. V.; Tripp, S. L.; Balasubramanian, R. Resorcinarene-Encapsulated Nanoparticles Building Blocks Self-Assembled Nanostructures. J. Inclusion Phenom. 2001, 41. DOI:  DOI: 10.1023/A:1014472212238
      There is no corresponding record for this reference.
    24. 24
      Smith, S. R.; Lipkowski, J. Guided Assembly of Two-Dimensional Arrays of Gold Nanoparticles on a Polycrystalline Gold Electrode for Electrochemical Surface- Enhanced Raman Spectroscopy. J. Phys. Chem. C 2018, 122, 7303– 7311,  DOI: 10.1021/acs.jpcc.8b01309
      24
      Guided Assembly of Two-Dimensional Arrays of Gold Nanoparticles on a Polycrystalline Gold Electrode for Electrochemical Surface-Enhanced Raman Spectroscopy
      Smith, Scott R.; Lipkowski, Jacek
      Journal of Physical Chemistry C (2018), 122 (13), 7303-7311CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Development of a reproducible two-dimensional array of gold nanoparticles (AuNPs) through a guided assembly approach and sequentially using an electrochem. cleaning procedure to remove all capping ligands and surface contaminants for studying gluconate, a weak Raman scatterer, with electrochem. surface-enhanced Raman spectroscopy (SERS) is discussed. Here, a unique use of shell-isolated nanoparticles (NPs) is presented by employing a thin-cell configuration during NP deposition to obtain a highly reproducible monolayer of AuNPs with spacing by 2× the SiO2 shell thickness. Upon SiO2 dissoln. and electrochem. cleaning, a well-ordered arrangement of bare AuNPs was achieved. The SERS active electrode modified with NP arrays was used for the characterization of gluconate adsorption. Enhanced spot-to-spot reproducibility of the SERS signal was achieved, allowing for significant redn. in the acquisition time needed for recording SERS spectra and investigation of gluconate adsorption on gold surfaces at short times. The results collected suggest that gluconate has undergone some electrooxidn. but remains well-hydrated in the interfacial region.
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    25. 25
      Shibamoto, K.; Yasumuro, S.; Horiuchi, K.; Teraoka, T.; Fujita, T. Study of Two-dimensional Highly-ordering of Gold Nanoparticles for an Optical Sensor Using Surface Plasmon Excitation as an Assistance Effect. Bunseki Kagaku 2014, 63, 293– 298,  DOI: 10.2116/bunsekikagaku.63.293
      25
      Study of two-dimensional highly-ordering of gold nanoparticles for an optical sensor using surface plasmon excitation as an assistance effect
      Shibamoto, Kohei; Yasumuro, Syunsuke; Horiuchi, Kentaro; Teraoka, Takuma; Fujita, Takashi
      Bunseki Kagaku (2014), 63 (4), 293-298CODEN: BNSKAK; ISSN:0525-1931. (Nippon Bunseki Kagakkai)
      The authors succeeded to fabricate a two-dimensional array of gold nanoparticles with high-ordering by using the surface plasmon excitation of gold nanoparticles for enhancing the repulsive force and controlling the aggregation through the process of fabrication. From SEM observations and spectroscopic measurements, we evaluated the order of the two-dimensional array of gold nanoparticles while taking account of particle isolation. Moreover, the high-ordering of the two-dimensional array provides higher sensitivity and higher reproducibility of Raman measurements. From these results, it is expected that the fabricated two-dimensional array of gold nanoparticles will lead to applications for a mol. sensor.
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    26. 26
      Shibamoto, K.; Kitajima, M.; Mohammad, K. H.; Patent, K. I. Fabrication of single layer array structure of surface unmodified metal nanoparticles. JP 4900550 B2, 2012.
      There is no corresponding record for this reference.
    27. 27
      Hentschel, M.; Dregely, D.; Vogelgesang, R.; Giessen, H.; Liu, N. Plasmonic Oligomers: The Role of Individual Particles in Collective Behavior. ACS Nano 2011, 5, 2042– 2050,  DOI: 10.1021/nn103172t
      27
      Plasmonic Oligomers: The Role of Individual Particles in Collective Behavior
      Hentschel, Mario; Dregely, Daniel; Vogelgesang, Ralf; Giessen, Harald; Liu, Na
      ACS Nano (2011), 5 (3), 2042-2050CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      A comprehensive exptl. study is presented of the optical properties of plasmonic oligomers. Both the constitution and configuration of plasmonic oligomers have a large influence on their resonant behavior, which draws a compelling analogy to mol. theory in chem. To elucidate the constitution influence, the size of individual nanoparticles were varied and the role identified of the target nanoparticle from the spectral change. To illustrate the configuration influence, the positions and nos. of nanoparticles in a plasmonic oligomer was varied. A large spectral red shift at the transition from displaced nanoparticles to touching ones was demonstrate exptl. The oligomeric design strategy opens up a rich pathway for the implementation of optimized optical properties into complex plasmonic nanostructures for specific applications.
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    28. 28
      Kneipp, K.; Kneipp, H.; Itzkan, I.; Dasari, R. R.; Feld, M. S. Single Molecule Detection Using near Infrared Surface-Enhanced Raman Scattering. Single Molecule Spectroscopy; Series in Chemical Physics; Springer, 2001; pp 144– 160.
      There is no corresponding record for this reference.
    29. 29
      Jiang, J. D.; Burstein, E.; Kobayashi, H. Resonant Raman Scattering by Crystal-Violet Molecules Adsorbed on a Smooth Gold Surface: Evidence for a Charge-Transfer Excitation. Phys. Rev. Lett. 1986, 57, 1793– 1796,  DOI: 10.1103/PhysRevLett.57.1793
      29
      Resonant Raman scattering by crystal-violet molecules adsorbed on a smooth gold surface: evidence for a charge-transfer excitation
      Jiang, J. D.; Burstein, E.; Kobayashi, H.
      Physical Review Letters (1986), 57 (14), 1793-6CODEN: PRLTAO; ISSN:0031-9007.
      Measurements are reported of excitation-profile spectra for Raman scattering from the central-C breathing mode of crystal violet adsorbed on a smooth Au surface. For polarization configurations that involve the xx (or yy) component of the Raman tensor, the spectra exhibit a resonance peak corresponding to the 1st singlet π-π* electronic excitation of adsorbed crystal-violet ions. The spectrum for the zz component does not exhibit this feature, but rather exhibits a steadily increasing scattering intensity with wavelength, that is attributed to an intermol. charge-transfer electronic excitation.
      >> More from SciFinder ®
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    30. 30
      Cañamares, M. V.; Chenal, C.; Birke, R. L.; Lombardi, J. R. DFT, SERS, and Single-Molecule SERS of Crystal Violet. J. Phys. Chem. C 2008, 112, 20295– 20300,  DOI: 10.1021/jp807807j
      There is no corresponding record for this reference.
    31. 31
      Shibamoto, K.; Sakata, K.; Nagoshi, K.; Korenaga, T. Laser Desorption Ionization Mass Spectrometry by Using Surface Plasmon Excitation on Gold Nanoparticle. J. Phys. Chem. C 2009, 113, 17774– 17779,  DOI: 10.1021/jp9020432
      31
      Laser Desorption Ionization Mass Spectrometry by Using Surface Plasmon Excitation on Gold Nanoparticle
      Shibamoto, K.; Sakata, K.; Nagoshi, K.; Korenaga, T.
      Journal of Physical Chemistry C (2009), 113 (41), 17774-17779CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      The authors show development of a laser desorption/ionization (LDI) method with ultrahigh sensitivity by adding Au nanoparticles with a diam. of several tens of nanometers into a sample soln. The authors succeeded in detection of an ultratrace amt. of sample mols., which is less than several hundred zeptomoles. Probably the charge interaction based on surface plasmon (SP) excitation is very effective for ultrahigh sensitivity in LDI method.
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    32. 32
      Vinod, M.; Gopchandran, K. G. Au, Ag and Au:Ag Colloidal Nanoparticles Synthesized by Pulsed Laser Ablation as SERS Substrates. Prog. Nat. Sci.: Mater. Int. 2014, 24, 569– 578,  DOI: 10.1016/j.pnsc.2014.10.003
      32
      Au, Ag and Au:Ag colloidal nanoparticles synthesized by pulsed laser ablation as SERS substrates
      Vinod, M.; Gopchandran, K. G.
      Progress in Natural Science: Materials International (2014), 24 (6), 569-578CODEN: PNSMBB ISSN:. (Elsevier B.V.)
      CP colloidal suspensions of gold and silver nanoparticles were synthesized using pulsed laser ablation. The dependence of laser fluence on the surface plasmon characteristics of the nanoparticles was investigated. Au:Ag colloidal suspensions were prepd. by mixing highly monodisperse Au and Ag nanocolloids. The plasmon band of these mixts. was found to be highly sensitive to Au:Ag concn. ratio and wavelength of the laser beam used in the ablation process. The Au:Ag mixt. consists of almost spherical shaped nanostructures with a tendency to join with adjacent ones. The surface enhanced Raman scattering activity of the Au, Ag and Au:Ag colloidal suspensions was tested using crystal violet as probe mols. Enhancement in Raman signal obtained with Au:Ag substrates was found to be promising and strongly depends on its plasmon characteristics.
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    33. 33
      Lin, S.; Lin, X.; Song, X.; Han, S.; Wang, L.; Hasi, W. Fabrication of Flexible Paper - Based Surface - Enhanced Raman Scattering Substrate from Au Nanocubes Monolayer for Trace Detection of Crystal Violet on Shell. J. Raman Spectrosc. 2019, 50, 1074– 1084,  DOI: 10.1002/jrs.5620
      33
      Fabrication of flexible paper-based Surface-enhanced Raman scattering substrate from Au nanocubes monolayer for trace detection of crystal violet on shell
      Lin, Shuang; Lin, Xiang; Song, Xueying; Han, Siqingaowa; Wang, Li; Hasi, Wuliji
      Journal of Raman Spectroscopy (2019), 50 (8), 1074-1084CODEN: JRSPAF; ISSN:0377-0486. (John Wiley & Sons Ltd.)
      Surface-enhanced Raman scattering (SERS) substrate is the key to SERS technol. and it is still a basic focus to fabricate desirable SERS substrates offering multiple advantages of strong Raman enhancement and good reproducibility and portability. A flexible paper-based SERS substrate were fabricated involving the use of Au nanocubes (NCs) monolayer. Au NCs were generated with tunable size in the range of 24 to 63 nm through seed-mediated growth method. The effect of support on SERS properties of Au NCs-assembled monolayer was systemically explored. As a result, more excellent SERS performance could be obtained by assembling Au NCs on the filter paper. Besides, the influence of Au NCs' size on SERS-enhanced effect of paper-based substrate was also investigated. Our results clearly indicated that paper-based substrate with 39 nm Au NCs possessed the optimal SERS enhancement. This SERS substrate exhibited high sensitivity with enhancement factor (EF) up to 9.75 ×107 and demonstrated good uniformity and time stability. Furthermore, based on this superior paper-based SERS substrate with advantage of powerful sample extn. performance, the measurement of crystal violet (CV) on shell surface were successfully carried out with detection limit down to 2.17 × 10-7 M. And linear quantification were achieved in the range from 5 × 10-5 to 5 × 10-7 M. To sum up, the as-prepd. SERS substrate is applicable for on-site detection and anal. of CV on various shell surfaces.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXptFKmt74%253D&md5=149ce154178968de655cab6132507bee
    34. 34
      Kneipp, K.; Kneipp, H.; Itzkan, I.; Dasari, R. R.; Feld, M. S. Ultrasensitive Chemical Analysis by Raman Spectroscopy. Chem. Rev. 1999, 99, 2957– 2976,  DOI: 10.1021/cr980133r
      34
      Ultrasensitive chemical analysis by Raman spectroscopy
      Kneipp, Katrin; Kneipp, Harald; Itzkan, Irving; Dasari, Ramachandra R.; Feld, Michael S.
      Chemical Reviews (Washington, D. C.) (1999), 99 (10), 2957-2975CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
      A review with 133 refs. is given on surface-enhanced Raman scattering, single-mol. Raman spectroscopy, crit. anal. and prospects of single-mol. Raman spectroscopy.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXmt12nt7Y%253D&md5=8b8a874a1f9d7494d5568ac1921d459b
    35. 35
      Shibamoto, K.; Katayama, K.; Sawada, T. Fundamental Processes of Surface Enhanced Raman Scattering Detected by Transient Reflecting Grating Spectroscopy. J. Photochem. Photobiol., A 2003, 158, 105– 110,  DOI: 10.1016/S1010-6030(03)00023-6
      35
      Fundamental processes of surface enhanced Raman scattering detected by transient reflecting grating spectroscopy
      Shibamoto, Kohei; Katayama, Kenji; Sawada, Tsuguo
      Journal of Photochemistry and Photobiology, A: Chemistry (2003), 158 (2-3), 105-110CODEN: JPPCEJ; ISSN:1010-6030. (Elsevier Science B.V.)
      Ultrafast charge transfer (CT) between gold and crystal violet (CV) mols. in relation with the surface enhanced Raman scattering (SERS) activation was investigated using the transient reflecting grating (TRG) spectroscopic method. A charge transfer between gold and crystal violet was obsd. only for the SERS-active substrate and it occurred within 200 fs. Since the adsorbed dyes had electronic overlap with the metal substrate at the point of central carbon, considering the difference of the Raman spectra between adsorbed and free dyes, it was suggested that the charge transfer occurred through the central carbon of crystal violet. Furthermore, it was shown that the surface morphol. of the substrates is in close correlation with the charge transfer process from its dependence on the prepn. method of substrates.
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    36. 36
      Shibamoto, K.; Katayama, K.; Sawada, T. Ultrafast Charge Transfer in Surface-Enhanced Raman Scattering (SERS) Processes Using Transient Reflecting Grating (TRG) Spectroscopy. Chem. Phys. Lett. 2007, 433, 385– 389,  DOI: 10.1016/j.cplett.2006.11.036
      36
      Ultrafast charge transfer in surface-enhanced Raman scattering (SERS) processes using transient reflecting grating (TRG) spectroscopy
      Shibamoto, Kohei; Katayama, Kenji; Sawada, Tsuguo
      Chemical Physics Letters (2007), 433 (4-6), 385-389CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
      Ultrafast dynamics was studied for photoexcited electrons between a SERS-active Au substrate and several kinds of adsorbed dyes by using TRG spectroscopy. A charge transfer (CT) within 200 fs between them was obsd. for a SERS-active sample and the no. of CT electrons had a strong correlation to both the relative adsorption energy states (AESs) of dyes and the enhancement factors of their SERS band. To increase the no. of CT electrons, the AESs should be closer to the excited energy state of Au. A larger no. of CT electrons are considered to make the enhancement of SERS band larger.
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    37. 37
      Deegan, R. D.; Bakajin, O.; Dupont, T. F.; Huber, G.; Nagel, S. R.; Witten, T. A. Capillary Flow as the Cause of Ring Stains from Dried Liquid Drops. Nature 1997, 389, 827– 829,  DOI: 10.1038/39827
      37
      Capillary flow as the cause of ring stains from dried liquid drops
      Deegan, Robert D.; Bakajin, Olgica; Dupont, Todd F.; Huber, Greg; Nagel, Sidney R.; Witten, Thomas A.
      Nature (London) (1997), 389 (6653), 827-829CODEN: NATUAS; ISSN:0028-0836. (Macmillan Magazines)
      When a spilled drop of coffee dries on a solid surface, it leaves a dense, ring-like deposit along the perimeter. The coffee - initially dispersed over the entire drop - becomes concd. into a tiny fraction of it. Such ring deposits are common wherever drops contg. dispersed solids evap. on a surface, and they influence processes such as printing, washing and coating. Ring deposits also provide a potential means to write or deposit a fine pattern onto a surface. Here we ascribe the characteristic pattern of the deposition to a form of capillary flow in which pinning of the contact line of the drying drop ensures that liq. evapg. from the edge is replenished by liq. from the interior. The resulting outward flow can carry virtually all the dispersed material to the edge. This mechanism predicts a distinctive power-law growth of the ring mass with time - a law independent of the particular substrate, carrier fluid or deposited solids. We have verified this law by microscopic observations of colloidal fluids.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.2c04032.

    • SEM images of SW substrates, dependence of Raman peak intensity on the dipping time, and literature data for SERS substrates using Au NPs (DOCX)


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