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Physical Insights into Materials and Molecular Properties

Oppositely Charged Nanoparticles Precipitate Not Only at the Point of Overall Electroneutrality
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  • Masaki Itatani
    Masaki Itatani
    Department of Physics, Institute of Physics, Budapest University of Technology and Economics, Műegyetem rkp. 3, Budapest H-1111, Hungary
    More by Masaki Itatani
    Orcidhttps://orcid.org/0000-0003-1025-0452
  • Gábor Holló
    Gábor Holló
    ELKH-BME Condensed Matter Research Group, Műegyetem rkp. 3, Budapest H-1111, Hungary
    Department of Fundamental Microbiology, University of Lausanne, Biophore Building, CH-1015 Lausanne, Switzerland
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  • Dániel Zámbó
    Dániel Zámbó
    Centre for Energy Research, Institute of Technical Physics and Materials Science, Konkoly-Thege út 29-33, Budapest H-1120, Hungary
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  • Hideyuki Nakanishi
    Hideyuki Nakanishi
    Department of Macromolecular Science and Engineering, Graduate School of Science and Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
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    Orcidhttps://orcid.org/0000-0001-8065-6373
  • András Deák*
    András Deák
    Centre for Energy Research, Institute of Technical Physics and Materials Science, Konkoly-Thege út 29-33, Budapest H-1120, Hungary
    *(A.D.) Email: [email protected]
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  • István Lagzi*
    István Lagzi
    Department of Physics, Institute of Physics, Budapest University of Technology and Economics, Műegyetem rkp. 3, Budapest H-1111, Hungary
    ELKH-BME Condensed Matter Research Group, Műegyetem rkp. 3, Budapest H-1111, Hungary
    *(I.L.) Email: [email protected]
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    Orcidhttps://orcid.org/0000-0002-2303-5965
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The Journal of Physical Chemistry Letters

Cite this: J. Phys. Chem. Lett. 2023, 14, 40, 9003–9010
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https://doi.org/10.1021/acs.jpclett.3c01857
Published October 2, 2023

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Abstract

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Precipitation of oppositely charged entities is a common phenomenon in nature and laboratories. Precipitation and crystallization of oppositely charged ions are well-studied and understood processes in chemistry. However, much less is known about the precipitation properties of oppositely charged nanoparticles. Recently, it was demonstrated that oppositely charged gold nanoparticles (AuNPs), also called nanoions, decorated with positively or negatively charged thiol groups precipitate only at the point of electroneutrality of the sample (i.e., the charges on the particles are balanced). Here we demonstrate that the precipitation of oppositely AuNPs can occur not only at the point of electroneutrality. The width of the precipitation window depends on the size and concentration of the nanoparticles. This behavior can be explained by the aggregation of partially stabilized clusters reaching the critical size for their sedimentation in the gravitational field.

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Understanding the self-assembly of nanoscopic building blocks is one of the essential challenges in nanoscience and nanotechnology. (1−5) Answering the related questions raised is important not only from the fundamental but also from the applied science point of view. Untangling the general processes and exploring the main interactions existing between the building blocks allow us to control and drive the assembly, generating various hierarchical and higher-order structures. (6−9)

There are several governing forces at the nanoscale that order the self-assembly. Among them, two interactions, the attractive van der Waals (VdW) and electric double-layer interactions, are dominant. (10−13) Competition between these two interactions can generate various equilibrium and out-of-equilibrium structures ranging from one to three dimensions. (14−18) These two interactions regulate the aggregation and precipitation of the oppositely charged nanoparticles (NPs) as well. (19) Precipitation, including nucleation and growth processes from ions, is a well-understood phenomenon from the thermodynamic as well as kinetic points of view. (20−23) However, much less is known about the precipitation of oppositely charged spherical nanoparticles (NPs), also called nanoions.

Previous studies in the past two decades showed that oppositely charged NPs precipitate rapidly only at the point of electroneutrality, wherein their charges are macroscopically compensated. (24−31) Later this empirical statement was extended with the statement that the oppositely charged NPs exhibit this behavior at the point of overall electroneutrality only if the concentration of NPs exceeds a threshold concentration (termed precipitation threshold concentration). (32)

It has been shown earlier that very small (a few nanometers in diameter), oppositely charged nanoparticles show ionic-like behavior during their aggregation, and large, ordered nanoparticle crystals are formed at the point of the overall electroneutrality, where the aggregate formation can be qualitatively described considering the free-energy change associated with the ordered nanoparticle-crystal formation. (33) As for these “nanoions”, the electric double-layer interaction has an effective range comparable to that of the particle diameter. The solubility of the precipitate of nanoions can be considered to be zero, and when one polarity of nanoions is in excess, the formation of core–shell structures can be anticipated; that is, the minority component is shielded by the majority of NPs, resulting in small nanoparticle clusters that can remain stable over time without significant sedimentation. (24) For larger particle diameters, similar behavior can be expected, but as their concentrations become similar, an earlier onset of sedimentation might occur.

Here we show that this empirical law of the precipitation of oppositely charged NPs should be extended further with the fact that the precipitation occurs not only at the point of the electroneutrality, but rather there is a certain precipitation window around the electroneutrality, enabling the particle–particle assembly. The width of this precipitation window depends on the size of the NPs and the concentration of the NP solutions. In our study, we follow the definition suggested by the International Union of Pure and Applied Chemistry (IUPAC) for chemical precipitation, namely, precipitation is the process in which a solid material sediments from a liquid solution. (34)

To investigate the precipitation behavior of oppositely charged AuNPs, we used three different sizes of AuNPs (2.2, 4.6, and 9.1 nm) and sample concentrations (0.56 and 0.26 mM in terms of gold atoms, corresponding to extinction values at the peak of the surface plasmon resonance of 1.7 and 0.8, respectively). Before the precipitation experiments, we verified that the precipitation point when a rapid (on the time scale of several ten seconds) precipitation occurred─expressed as a ratio of the amount of the negatively (n–) and all charged (n– + n+) NPs (χ = n–/(n–+ n+))─was close to 0.5 within an experimental error of 5% by an electrostatic titration using the solutions of oppositely charged AuNPs of 0.56 mM. This procedure was described in detail in our previous study. (32) Our finding indicated that the numbers of positively and negatively charged thiols attached to the surfaces of AuNPs were equal on average, which is consistent with the findings published in other studies. (24,32) The details of the experiments can be found in the Supporting Information.

In the experiments (Figure 1), two solutions of oppositely charged AuNPs with various volume ratios were mixed in a plastic cuvette, keeping the overall particle concentration constant. This procedure differed from the method used in previous studies in which the authors titrated the solution of one polarity with the solution of oppositely charged AuNPs. (24,25) Whereas the individual samples are stable, both the electric double layer and dispersion interactions are attractive between the oppositely charged particle types, resulting in a net attractive interaction on the order of several tens of kT (Figure S1) that leads to their rapid heteroaggregation. (35) It has to be emphasized that the applied volume ratio also corresponds to the ratio of the total charges introduced into the samples. After mixing, the solutions were left undisturbed at room temperature. After 1 h, the extinction of the samples was measured by UV–vis spectrophotometry, and the values were extracted at λ = 523 nm, corresponding to the initial plasmon resonance peak as well as at λ = 400 nm, where the absorption is solely determined by the interband transitions in gold and hence can be used to assess the amount of Au0 in the light path. (36−38) We chose 1 h for the precipitation experiments because it was reported that the electrostatic precipitation occurred in a few ten seconds at the point of electroneutrality. (24,29,32) Therefore, 1 h (which is around 2 orders of magnitude greater than the time scale of the precipitation at the point of electroneutrality) was a reasonable choice to investigate the colloidal stability of the samples. The precipitation consists of two distinct, consecutive, and well-separated steps that can be easily followed by UV–vis spectroscopy. The first step is the aggregation of AuNPs into clusters, which can be resolved by a red-shift in the spectrum and an increase of the peak of the extinction, consistent with the plasmon coupling upon particle clustering. (39) The cluster growth or eventual cluster-to-cluster aggregation leads to the loss of dispersion stability, which is manifested in the sedimentation of the sample. Further, these clusters lose their colloidal stability upon being merged into larger clusters and sediment from the solution. This process leads to a decreasing sample extinction. In other words, the formation of clusters and their destabilization (sedimentation) can be monitored and distinguished by measuring the extinction of the samples.

Figure 1

Figure 1. (a) TEM micrographs and (b) size distribution of the AuNPs used in the precipitation experiments of the oppositely charged NPs. (c) The precipitation process of the oppositely charged AuNPs consists of two consecutive steps: (1) aggregation of NPs into clusters manifested in a red-shift of the spectrum (due to an increase of the particle size) and an increase of the extinction (because the red-shifted mode has a larger extinction cross section) and (2) coagulation of these clusters which sediment from the solution manifested in a decrease of the extinction.

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Figure 2 shows the results of the electrostatic precipitation of oppositely charged AuNPs. In all mixing ratios, the aggregation of AuNPs into clusters occurred, and the dispersion stability is partially or completely lost. Further away χ = 0.5 (i.e., from the overall electroneutrality), clusters are still formed but remained in the solution. The former can be inferred from the slight increase in the extinction of the samples measured at λ = 523 nm and the pronounced color change from red to purple (Figure 2a,b). Closer to macroscopic electroneutrality, the generated clusters coagulated and formed larger aggregates that sedimented from the liquid phase of the samples. This process manifests in a significant decrease in the extent of extinction and the appearance of the sediments at the bottom of the cuvettes. It has to be pointed out that the width of the symmetric precipitation “window” near χ = 0.5 depends on the size and the concentration of the solutions (Figure 2b). The size effect can be explained by considering the net colloidal interaction between the spheres. In the present system, both the electric double layer and van der Waals interactions promote particle aggregation as a result of attraction. It has to be emphasized, however, that the van der Waals interaction scales with the second order of the radius; hence, a small increase in particle size can result in larger attraction, especially if one considers that the Hamaker coefficient for the gold/water/gold system is a factor larger than usual (∼2.5 × 10–19 J) due to the polarizability of the particles. (40) Thus, the extent of colloidal stability of nanoparticle clusters consisting of the same number of NPs depends on the size of the building blocks: the smaller the NP size, the larger the cluster stability. This dependency is further explained via our model calculations (vide infra). At a lower concentration of the AuNPs (0.26 mM), the size of the formed clusters was smaller, improving the stability of the small aggregates in a larger mixing ratio range (the precipitation window shrank (Figures 2c and S2).

Figure 2

Figure 2. (a) Photographs of the mixtures of the oppositely charged AuNPs applying various mixing ratios after 1 h, starting the experiments using (i) large, (ii) medium, and (iii) small AuNPs with the concentration of 0.56 mM (in terms of gold atoms). (b) Extinction of oppositely charged AuNP mixtures at various mixing ratios after 1 h starting the experiments using AuNPs with the concentration of (b) 0.56 mM and (c) 0.26 mM (measured at λ = 523 nm). The red, green, and blue colors correspond to the small, medium, and large NPs, respectively.

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To support the experimental observations, we performed DLS and zeta potential measurements (Figures 3 and S3). In these experiments, the measurements were started immediately after the mixing of solutions of the oppositely charged AuNPs. These measurements confirmed that at χ = 0.5, the precipitation process is the fastest because in this case the formed clusters have the largest size with close to zero zeta potential. Farther from the overall electroneutrality, the size of the clusters decreased and approached the average size of ∼100 nm, where clusters were stable in the water phase as their zeta potential magnitude was ∼40 mV. Interestingly, in small mixing ratios (mixing ratio below 0.3 and above 0.7) the magnitude of the zeta potential slightly increased, which is more expressed in the case of small NPs. This effect can be explained based on the heteroaggregation in the presence of large excess of one of the components: the minority components are effectively shielded by the majority particles, preventing excessive aggregation and consequent sedimentation. Simultaneously, in the same mixing ratio range, the size increases compared to the free particles, confirming heteroaggregation, but remains fairly constant and increases further only as the mixing ratio approaches the value of 0.5. This indicates that a certain limit in terms of the cluster size must be exceeded to observe the overall loss of colloidal stability in the solutions.

Figure 3

Figure 3. Dependence of (a) the hydrodynamic size (measured by DLS and calculated as an average of the population) and (b) the zeta potential of the clusters formed in the interaction of the oppositely charged NPs on the mixing ratio (χ). The red, green, and blue colors correspond to the small, medium, and large NPs, respectively. The concentration of the solutions of oppositely charged AuNPs was 0.75 mM.

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Whereas the observations above are restricted to the behavior right after mixing, the clustering was further investigated for 1 h to create a connection between the instantaneous behavior of the system and the dispersion stability-related sedimentation as a function of time (Figure 4). As heteroaggregation and sedimentation might proceed simultaneously, different quantities have been monitored both during DLS and spectroscopy measurements. Figure 4a shows the intensity-based size evolution of the medium sample at a composition (χ = 0.6), which is inside the precipitation window (see Figure 2a(ii)). It is clear that the initial ca. 100 nm cluster size mentioned earlier right after mixing further increased up to the micrometer range after 1 h. In contrast, for a sample outside the precipitation window (χ = 0.7) the cluster size remains constant at around 100 nm (Figure S4). At the same time, the count rate measured during this 1 h time period starts high and decreases monotonically in the case of χ = 0.6, indicating rapid aggregation followed by steady sedimentation. In contrast, at χ = 0.7 a small count rate increase in the first 10 min shows an ever slowing aggregation leading to stable clusters. This is corroborated by the spectral data of the same systems. The plasmon shift (Figure 4c) changes rapidly within our time resolution (1 min), and the peak position remains almost constant for χ = 0.7, whereas a more pronounced shift is found for χ = 0.6 with similar kinetics as observed for the size change in Figure 4a. The extinction measured at 400 nm related to the Au0 content in the light path (Figure 4d) confirms the continuous removal of the particles because of sedimentation when the composition is inside the precipitation window (χ = 0.6), whereas clearly higher dispersion stability is found for the χ = 0.7 composition.

Figure 4

Figure 4. Time-dependent parameters of the medium-sized (4.6 nm) system corresponding to compositions inside (χ = 0.6) and outside (χ = 0.7) of the sedimentation window. The intensity size distribution showing the inside case (a) and overall count rates (b) have been obtained from dynamic light scattering measurements, while the plasmon peak position shift (c) and extinction measured at 400 nm have been extracted from the optical spectra (d).

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The same was found for the other two particle sizes (Figures S5 and S6); when χ lies outside the precipitation window, a stable cluster size of around 100 nm is obtained (Figure S4). Inside the window, on the other hand, larger aggregates are formed, leading to sedimentation (for the small-sized sample, the cluster size remains fairly constant though), and the corresponding plasmon peak shifts scale with the particle size as expected (larger particles provide larger shifts). At the same time, the count rate and extinction values are consistent in effectively capturing the sample sedimentation.

To further support the experimental observations, we can construct a mathematical model. The measurements have shown that even if the sample composition is not fulfilling the overall electroneutrality (that is, χ differs from 0.5), clusters are still formed, and the mobility is determined by the charge of the excess particle type. Accordingly, in our simplified model, we assume that at any composition in the internal part of the aggregates the charges are balanced, i.e., the numbers of the oppositely charged NPs are the same, and they form a face-centered cubic crystal lattice. The surface of the aggregates is, however, completely covered by the excess, like charged NPs, which generate a net charge for them. In our model, if the radius of the aggregate (R) reaches a critical value (Rc), the formed aggregates sediment from the solution.

Because the lattice constant of a face-centered cubic (FCC) grid is 22r and it contains two particles, the unit cell area of a single NP on the cluster surface (composed of the excess particles) can be expressed as

A^=4r2
(1)
where r is the radius of the NPs. As the volume fraction in the lattice is given by π32, the volume taken by a single NP in the aggregate is
V^=43πr3π32=42r3
(2)
The volume and surface area of the aggregates can be expressed as
V=43πR3=n++n−NV^
(3)
A=4πR2=|n+−n−|NA^
(4)
where n+ and n– are the initial numbers of the positively and negatively charged AuNPs in the sample, respectively, and N is the number of aggregates in the sample. In the equations (n+ + n–)/N gives the number of particles the clusters consist of while |n+ – n–|/N is the excess on the surface of the aggregates. It has to be emphasized that the cluster surface is covered by the excess particles; hence, their number can be used to derive the surface area of the aggregate. The radius of the cluster (R) and the number of the aggregates (N) can be expressed from eqs 3 and 4 combining with eqs 1 and 2
R=32n++n−|n+−n−|r
(5)
N=118π|n+−n−|3(n++n−)2
(6)
Analyzing the results of this model (eqs 5 and 6, Figure 5), one can conclude the following findings. The size of the aggregates increases with the size of the NPs (eq 5); thus, in the case of larger NPs the critical radius for sedimentation is reached faster (i.e., the precipitation window is wider for larger NPs). The radius of the aggregates is proportional to the amount (concentration) of the oppositely charged NPs (eq 5; i.e., the precipitation window is wider at higher concentrations of NPs). These two conclusions are in good accordance with the experimental results. The model also implies that the number (concentration) of aggregates does not depend on the size of the NPs (eq 6). Additionally, by increasing the number of the oppositely charged NPs, the number of aggregates decreases in the samples. It should be noted that this model has a singularity at n+ = n–, and if n+ approaches n– (or vice versa), the size and number of the aggregates go to infinity and zero (i.e., having only one large aggregate at n+ = n–). The model calculations also point out the governing role of the particle size in the cluster stability at different mixing ratios: while the concentration of the clusters does not change upon increasing the size of the building blocks, the dimension of the clusters dictates the stability of the colloidal solutions. The observed mixing-ratio-dependent instability, thus, is a consequence of the increasing interparticle attraction upon increasing the size of the building blocks within the formed clusters.

Figure 5

Figure 5. Results of the equilibrium model simulations on the precipitation window using smaller (r = 1) and larger (r = 5) oppositely charged NPs. The red color corresponds to the size of the clusters that reach the critical size (Rc = 100) and sediment from the solution. nmax is the highest initial number of like charged AuNPs.

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Here the aim was to develop a minimal model for a qualitative description (with the least possible number of variables) that can highlight the driving force of the phenomena, namely, a simple geometrical arrangement of the NPs. In this approach, to calculate the precipitation window, only the ratio of the oppositely charged NPs and their radii was necessary. To develop such a minimal model, some strong assumptions were required. However, in the Supporting Information, an extended model is presented, which shows that one can observe the same qualitative results with more realistic assumptions introducing further additional parameters, namely, there are free oppositely charged NPs in the system during the precipitation (Figures S7 and S8).

Finally, it is an important issue of how the dispersity of the sample affects the precipitation behavior of the oppositely charged AuNPs. To investigate this effect, polydisperse samples of the oppositely charged AuNPs were created by mixing the like-charged solutions of small, medium, and large AuNPs, keeping the concentration of samples at 0.56 mM in terms of gold atoms in a way that samples contained 10%, 80%, and 10% and 30%, 40%, and 30% small, medium, and large AuNPs in terms of number of NPs, respectively. In the polydisperse samples, the average size of AuNPs increased only by 6% and 15% (from 4.6 to 4.9 and 5.3 nm), respectively. However, the standard deviation was doubled and tripled (from 0.7 to 1.4 and 2.5 nm, Figure S9a–c). The precipitation experiments were performed using these polydisperse samples of oppositely charged AuNPs at various χ values, and the results were compared with those obtained in the case of medium-sized AuNPs (Figures S9d and S10). It can be concluded that the results were similar to that of the medium-sized AuNPs even though the dispersity of the AuNPs samples increased significantly. Based on the photographs and UV–vis measurements of the samples, one can draw the conclusion that mainly the average size of the oppositely charged AuNPs governs the precipitation of NPs, and the dispersity of the sample plays a less significant role. This implies that the size of the major population of the nanoparticles is the crucial parameter in terms of the threshold cluster size, above which the aggregates start to precipitate at the investigated χ resolution.

A detailed understanding of the precipitation of oppositely charged NPs is a key issue not only from the fundamental point of view but also for designing and generating nanostructured materials for various applications. In this study, we present that the oppositely charged and like-sized AuNPs precipitate not only at the point of electroneutrality in the solutions. Based on our findings, the empirical law of precipitation can be revised by the fact that the precipitation process can also occur near the point of electroneutrality. We observed that in all cases when the oppositely charged AuNPs were mixed, irrespective of the ratio, stable clusters were formed with the size of ∼100 nm. Near the point of electroneutrality, these partially stabilized clusters could aggregate and sediment from the solution. We also showed that the precipitation behavior depends rather on the average size of the NPs than the dispersity of the samples. This knowledge can help in the engineering and design of nanostructured and hierarchical materials comprising oppositely charged particles with sizes ranging from nano- to micrometers.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpclett.3c01857.

  • Synthesis of gold nanoparticles and description of the measurements, description of the extended mathematical model, and Figures S1–S10 showing the calculated overall potentials, the precipitation of oppositely charged gold nanoparticles with the concentration of 0.26 mM; results of the extended mathematical model, and the effect of the dispersity of the sample on the precipitation window (PDF)

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Author Information

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  • Corresponding Authors
    • András Deák - Centre for Energy Research, Institute of Technical Physics and Materials Science, Konkoly-Thege út 29-33, Budapest H-1120, Hungary;  Email: [email protected]
    • István Lagzi - Department of Physics, Institute of Physics, Budapest University of Technology and Economics, Műegyetem rkp. 3, Budapest H-1111, Hungary;  ELKH-BME Condensed Matter Research Group, Műegyetem rkp. 3, Budapest H-1111, Hungary;  Orcidhttps://orcid.org/0000-0002-2303-5965;  Email: [email protected]
  • Authors
    • Masaki Itatani - Department of Physics, Institute of Physics, Budapest University of Technology and Economics, Műegyetem rkp. 3, Budapest H-1111, Hungary;  Orcidhttps://orcid.org/0000-0003-1025-0452
    • Gábor Holló - ELKH-BME Condensed Matter Research Group, Műegyetem rkp. 3, Budapest H-1111, Hungary;  Department of Fundamental Microbiology, University of Lausanne, Biophore Building, CH-1015 Lausanne, Switzerland
    • Dániel Zámbó - Centre for Energy Research, Institute of Technical Physics and Materials Science, Konkoly-Thege út 29-33, Budapest H-1120, Hungary
    • Hideyuki Nakanishi - Department of Macromolecular Science and Engineering, Graduate School of Science and Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan;  Orcidhttps://orcid.org/0000-0001-8065-6373
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This work was supported by the JSPS Postdoctoral Fellowship Program for Overseas Researchers (Identification Number 202260298), the National Research, Development and Innovation Office of Hungary (K131425, FK128327, and FK142148), and the National Research, Development, and Innovation Fund of Hungary under Grants of TKP2021-EGA-02 and TKP2021-NKTA-05.

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    A review. The creation of matter with varying degrees of complexities and desired functions is one of the ultimate targets of self-assembly. The ability to regulate the complex interactions between the individual components is essential in achieving this target. In this direction, the initial success of controlling the pathways and final thermodn. states of a self-assembly process is promising. Despite the progress made in the field, there has been a growing interest in pushing the limits of self-assembly processes. The main inception of this interest is that the intended self-assembled state, with varying complexities, may not be "at equil. (or at global min.)", rendering free energy minimization unsuitable to form the desired product. Thus, we believe that a thorough understanding of the design principles as well as the ability to predict the outcome of a self-assembly process is essential to form a collection of the next generation of complex matter. The present review highlights the potent role of finely tuned interparticle interactions in nanomaterials to achieve the preferred self-assembled structures with the desired properties. We believe that bringing the design and prediction to nanoparticle self-assembly processes will have a similar effect as retrosynthesis had on the logic of chem. synthesis. Along with the guiding principles, the review gives a summary of the different types of products created from nanoparticle assemblies and the functional properties emerging from them. Finally, we highlight the reasonable expectations from the field and the challenges lying ahead in the creation of complex and evolvable matter.
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    Huang, C.; Chen, X.; Xue, Z.; Wang, T. Effect of Structure: A New Insight into Nanoparticle Assemblies from Inanimate to Animate. Sci. Adv. 2020, 6 (20), eaba1321  DOI: 10.1126/sciadv.aba1321
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    Gu, Z.; Atherton, J. J.; Xu, Z. P. Hierarchical Layered Double Hydroxide Nanocomposites: Structure, Synthesis and Applications. Chem. Commun. 2015, 51 (15), 3024– 3036,  DOI: 10.1039/C4CC07715F
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    Hierarchical layered double hydroxide nanocomposites: structure, synthesis and applications
    Gu, Zi; Atherton, John James; Xu, Zhi Ping
    Chemical Communications (Cambridge, United Kingdom) (2015), 51 (15), 3024-3036CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    A review. Layered double hydroxide (LDH)-based nanocomposites, constructed by interacting LDH nanoparticles with other nanomaterials (e.g. silica nanoparticles and magnetic nanoparticles) or polymeric mols. (e.g. proteins), are an emerging yet active area in healthcare, environmental remediation, energy conversion and storage. Combining advantages of each component in the structure and functions, hierarchical LDH-based nanocomposites showed great potential in biomedicine, water purifn., and energy storage and conversion. This feature article summarizes the recent advances in LDH-based nanocomposites, focusing on their synthesis, structure, and application in drug delivery, bio-imaging, water purifn., supercapacitors, and catalysis.
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    Grötsch, R. K.; Wanzke, C.; Speckbacher, M.; Angı, A.; Rieger, B.; Boekhoven, J. Pathway Dependence in the Fuel-Driven Dissipative Self-Assembly of Nanoparticles. J. Am. Chem. Soc. 2019, 141 (25), 9872– 9878,  DOI: 10.1021/jacs.9b02004
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    Pathway Dependence in the Fuel-Driven Dissipative Self-Assembly of Nanoparticles
    Grotsch Raphael K; Wanzke Caren; Boekhoven Job; Speckbacher Maximilian; Angi Arzu; Rieger Bernhard
    Journal of the American Chemical Society (2019), 141 (25), 9872-9878 ISSN:.
    We describe the self-assembly of gold and iron oxide nanoparticles regulated by a chemical reaction cycle that hydrolyzes a carbodiimide-based fuel. In a reaction with the chemical fuel, the nanoparticles are chemically activated to a state that favors assembling into clusters. The activated state is metastable and decays to the original precursor reversing the assembly. The dynamic interplay of activation and deactivation results in a material of which the behavior is regulated by the amount of fuel added to the system; they either did not assemble, assembled transiently, or assembled permanently in kinetically trapped clusters. Because of the irreversibility of the kinetically trapped clusters, we found that the behavior of the self-assembly was prone to hysteresis effects. The final state of the system in the energy landscape depended on the pathway of preparation. For example, when a large amount of fuel was added at once, the material would end up kinetically trapped in a local minimum. When the same amount of fuel was added in small batches with sufficient time for the system to re-equilibrate, the final state would be the global minimum. A better understanding of pathway complexity in the energy landscape is crucial for the development of fuel-driven supramolecular materials.
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    van Ravensteijn, B. G. P.; Voets, I. K.; Kegel, W. K.; Eelkema, R. Out-of-Equilibrium Colloidal Assembly Driven by Chemical Reaction Networks. Langmuir 2020, 36 (36), 10639– 10656,  DOI: 10.1021/acs.langmuir.0c01763
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    Out-of-Equilibrium Colloidal Assembly Driven by Chemical Reaction Networks
    van Ravensteijn, Bas G. P.; Voets, Ilja K.; Kegel, Willem K.; Eelkema, Rienk
    Langmuir (2020), 36 (36), 10639-10656CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    A review. Transient assembled structures play an indispensable role in a wide variety of processes fundamental to living organisms including cellular transport, cell motility, and proliferation. Typically, the formation of these transient structures is driven by the consumption of mol. fuels via dissipative reaction networks. In these networks, building blocks are converted from inactive precursor states to active (assembling) states by (a set of) irreversible chem. reactions. Since the activated state is intrinsically unstable and can be maintained only in the presence of sufficient fuel, fuel depletion results in the spontaneous disintegration of the formed superstructures. Consequently, the properties and behavior of these assembled structures are governed by the kinetics of fuel consumption rather than by their thermodn. stability. This fuel dependency endows biol. systems with unprecedented spatiotemporal adaptability and inherent self-healing capabilities. Fascinated by these unique material characteristics, coupling the assembly behavior to mol. fuel or light-driven reaction networks was recently implemented in synthetic (supra)mol. systems. In this invited feature article, we discuss recent studies demonstrating that dissipative assembly is not limited to the mol. world but can also be translated to building blocks of colloidal dimensions. We highlight crucial guiding principles for the successful design of dissipative colloidal systems and illustrate these with the current state of the art. Finally, we present our vision on the future of the field and how marrying nonequil. self-assembly with the functional properties assocd. with colloidal building blocks presents a promising route for the development of next-generation materials.
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    Bishop, K. J. M.; Wilmer, C. E.; Soh, S.; Grzybowski, B. A. Nanoscale Forces and Their Uses in Self-Assembly. Small 2009, 5 (14), 1600– 1630,  DOI: 10.1002/smll.200900358
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    Nanoscale forces and their uses in self-assembly
    Bishop, Kyle J. M.; Wilmer, Christopher E.; Soh, Siowling; Grzybowski, Bartosz A.
    Small (2009), 5 (14), 1600-1630CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. The ability to assemble nanoscopic components into larger structures and materials depends crucially on the ability to understand in quant. detail and subsequently "engineer" the interparticle interactions. This Review provides a crit. examn. of the various interparticle forces (van der Waals, electrostatic, magnetic, mol., and entropic) that can be used in nanoscale self-assembly. For each type of interaction, the magnitude and the length scale are discussed, as well as the scaling with particle size and interparticle distance. In all cases, the discussion emphasizes characteristics unique to the nanoscale. These theor. considerations are accompanied by examples of recent exptl. systems, in which specific interaction types were used to drive nanoscopic self-assembly. Overall, this Review aims to provide a comprehensive yet easily accessible resource of nanoscale-specific interparticle forces that can be implemented in models or simulations of self-assembly processes at this scale.
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    Luo, Y.; Zhao, R.; Pendry, J. B. Van Der Waals Interactions at the Nanoscale: The Effects of Nonlocality. Proc. Natl. Acad. Sci. U. S. A. 2014, 111 (52), 18422– 18427,  DOI: 10.1073/pnas.1420551111
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    Van der Waals interactions at the nanoscale: The effects of nonlocality
    Luo, Yu; Zhao, Rongkuo; Pendry, John B.
    Proceedings of the National Academy of Sciences of the United States of America (2014), 111 (52), 18422-18427CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
    Calcd. using classical electromagnetism, the van der Waals force increases without limit as two surfaces approach. In reality, the force sats. because the electrons cannot respond to fields of very short wavelength: polarization charges are always smeared out to some degree and in consequence the response is nonlocal. Nonlocality also plays an important role in the optical spectrum and distribution of the modes but introduces complexity into calcns., hindering an anal. soln. for interactions at the nanometer scale. Here, taking as an example the case of two touching nanospheres, the authors show for the 1st time, to the authors' knowledge, that nonlocality in 3-dimensional plasmonic systems can be accurately analyzed using the transformation optics approach. The effects of nonlocality dramatically weaken the field enhancement between the spheres and hence the van der Waals interaction and to modify the spectral shifts of plasmon modes.
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    Walker, D. A.; Kowalczyk, B.; de la Cruz, M. O.; Grzybowski, B. A. Electrostatics at the Nanoscale. Nanoscale 2011, 3 (4), 1316– 1344,  DOI: 10.1039/C0NR00698J
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    Electrostatics at the nanoscale
    Walker, David A.; Kowalczyk, Bartlomiej; Olvera de la Cruz, Monica; Grzybowski, Bartosz A.
    Nanoscale (2011), 3 (4), 1316-1344CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
    A review. Electrostatic forces are amongst the most versatile interactions to mediate the assembly of nanostructured materials. Depending on exptl. conditions, these forces can be long- or short-ranged, can be either attractive or repulsive, and their directionality can be controlled by the shapes of the charged nano-objects. This Review is intended to serve as a primer for experimentalists curious about the fundamentals of nanoscale electrostatics and for theorists wishing to learn about recent exptl. advances in the field. Accordingly, the first portion introduces the theor. models of electrostatic double layers and derives electrostatic interaction potentials applicable to particles of different sizes and/or shapes and under different exptl. conditions. This discussion is followed by the review of the key exptl. systems in which electrostatic interactions are operative. Examples include electroactive and "switchable" nanoparticles, mixts. of charged nanoparticles, nanoparticle chains, sheets, coatings, crystals, and crystals-within-crystals. Applications of these and other structures in chem. sensing and amplification are also illustrated.
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    Ambrosetti, A.; Subashchandrabose, S.; Liu, B.; Silvestrelli, P. L. Tunable van Der Waals Interactions in Low-Dimensional Nanostructures. J. Chem. Phys. 2021, 154 (22), 224105,  DOI: 10.1063/5.0051235
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    Tunable van der Waals interactions in low-dimensional nanostructures
    Ambrosetti, Alberto; Subashchandrabose, S.; Liu, B.; Silvestrelli, Pier Luigi
    Journal of Chemical Physics (2021), 154 (22), 224105CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
    Non-covalent van der Waals interactions play a major role at the nanoscale, and even a slight change in their asymptotic decay could produce a major impact on surface phenomena, self-assembly of nanomaterials, and biol. systems. By a full many-body description of vdW interactions in coupled carbyne-like chains and graphenic structures, here, we demonstrate that both modulus and a range of interfragment forces can be effectively tuned, introducing mech. strain and doping (or polarizability change). This result contrasts with conventional pairwise vdW predictions, where the two-body approxn. essentially fixes the asymptotic decay of interfragment forces. The present results provide viable pathways for detailed exptl. control of nanoscale systems that could be exploited both in static geometrical configurations and in dynamical processes. (c) 2021 American Institute of Physics.
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    Xu, Q.; Zhao, X. Electrostatic Interactions versus van Der Waals Interactions in the Self-Assembly of Dispersed Nanodiamonds. J. Mater. Chem. 2012, 22 (32), 16416– 16421,  DOI: 10.1039/c2jm32918b
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    Electrostatic interactions versus van der Waals interactions in the self-assembly of dispersed nanodiamonds
    Xu, Qian; Zhao, Xiang
    Journal of Materials Chemistry (2012), 22 (32), 16416-16421CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
    4-5 Nm nanodiamonds tend to self-assemble into 100-200 nm nanodiamond aggregations and furthermore nanodiamonds in the early stages of the detonation process present fantastic twinned morphologies, indicating that there are strong interactions among these nanodiamonds. Herein, electrostatic interactions and van der Waals interactions between two nanodiamonds are explored using DFT computations in conjunction with Monte Carlo mol. simulations. It is indicated that the van der Waals forces are much stronger than the electrostatic forces for the unsatd. nanodiamonds. More importantly, two assembly features are exposed as follows: assembly has a preferential face-to-face orientation; assembly has a strong binding energy comparable to the dissocn. energy of C-C bonding, which is -116.1 kcal mol-1 for a 2.48 nm truncated octahedral nanodiamond. The results suggest that the strong forces holding the nanodiamond aggregation almost certainly attribute to the proposed strong van der Waals forces, which is of great importance in understanding the aggregative properties of nanodiamond.
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    Li, Y.; Li, H.; He, X. Self-Assembly of Binary Particles with Electrostatic and van Der Waals Interactions. Chin. J. Chem. Phys. 2014, 27 (4), 419– 427,  DOI: 10.1063/1674-0068/27/04/419-427
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    Self-assembly of Binary Particles with Electrostatic and van der Waals Interactions
    Li, Yan; Li, Hua-ping; He, Xue-hao
    Chinese Journal of Chemical Physics (2014), 27 (4), 419-427CODEN: CJCPA6; ISSN:1674-0068. (Chinese Physical Society)
    Nanoparticles with competitive interactions in soln. can aggregate into complex structures. In this work, the synergistic self-assembles of binary particles with electrostatic and van der Waals interactions are studied with the particle Langevin dynamics simulation using a simple coarse-grained particle model. Various aggregations such as spherical, stacking-disk and tube structures are obsd. by varying the particles size and the interaction strength. The aggregation structures are explained with the packing theories of amphiphilic mols. in soln. and diblock copolymers in bulk. When the opposite ions are introduced into soln., the distribution of structures in the phase diagram appears an obvious offset. The simulation result is helpful to deeply understand the formation mechanism of complex nanostructures of multicomponent particles in soln.
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    Bian, T.; Gardin, A.; Gemen, J.; Houben, L.; Perego, C.; Lee, B.; Elad, N.; Chu, Z.; Pavan, G. M.; Klajn, R. Electrostatic Co-Assembly of Nanoparticles with Oppositely Charged Small Molecules into Static and Dynamic Superstructures. Nat. Chem. 2021, 13 (10), 940– 949,  DOI: 10.1038/s41557-021-00752-9
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    Electrostatic co-assembly of nanoparticles with oppositely charged small molecules into static and dynamic superstructures
    Bian, Tong; Gardin, Andrea; Gemen, Julius; Houben, Lothar; Perego, Claudio; Lee, Byeongdu; Elad, Nadav; Chu, Zonglin; Pavan, Giovanni M.; Klajn, Rafal
    Nature Chemistry (2021), 13 (10), 940-949CODEN: NCAHBB; ISSN:1755-4330. (Nature Portfolio)
    Coulombic interactions can be used to assemble charged nanoparticles into higher-order structures, but the process requires oppositely charged partners that are similarly sized. The ability to mediate the assembly of such charged nanoparticles using structurally simple small mols. would greatly facilitate the fabrication of nanostructured materials and harnessing their applications in catalysis, sensing and photonics. Here we show that small mols. with as few as three elec. charges can effectively induce attractive interactions between oppositely charged nanoparticles in water. These interactions can guide the assembly of charged nanoparticles into colloidal crystals of a quality previously only thought to result from their co-crystn. with oppositely charged nanoparticles of a similar size. Transient nanoparticle assemblies can be generated using pos. charged nanoparticles and multiply charged anions that are enzymically hydrolyzed into mono- and/or dianions. Our findings demonstrate an approach for the facile fabrication, manipulation and further investigation of static and dynamic nanostructured materials in aq. environments.
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    Grzelczak, M.; Liz-Marzán, L. M.; Klajn, R. Stimuli-Responsive Self-Assembly of Nanoparticles. Chem. Soc. Rev. 2019, 48 (5), 1342– 1361,  DOI: 10.1039/C8CS00787J
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    Stimuli-responsive self-assembly of nanoparticles
    Grzelczak, Marek; Liz-Marzan, Luis M.; Klajn, Rafal
    Chemical Society Reviews (2019), 48 (5), 1342-1361CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    The capacity to respond or adapt to environmental changes is an intrinsic property of living systems that comprise highly-connected subcomponents communicating through chem. networks. The development of responsive synthetic systems is a relatively new research area that covers different disciplines, among which nanochem. brings conceptually new demonstrations. Esp. attractive are ligand-protected gold nanoparticles, which have been extensively used over the last decade as building blocks in constructing superlattices or dynamic aggregates, under the effect of an applied stimulus. To reflect the importance of surface chem. and nanoparticle core compn. in the dynamic self-assembly of nanoparticles, we provide here an overview of various available stimuli, as tools for synthetic chemists to exploit. Along with this task, the review starts with the use of chem. stimuli such as solvent, pH, gases, metal ions or biomols. It then focuses on phys. stimuli: temp., magnetic and elec. fields, as well as light. To reflect on the increasing complexity of current architectures, we discuss systems that are responsive to more than one stimulus, to finally encourage further research by proposing future challenges.
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    Deng, K.; Luo, Z.; Tan, L.; Quan, Z. Self-Assembly of Anisotropic Nanoparticles into Functional Superstructures. Chem. Soc. Rev. 2020, 49 (16), 6002– 6038,  DOI: 10.1039/D0CS00541J
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    Self-assembly of anisotropic nanoparticles into functional superstructures
    Deng, Kerong; Luo, Zhishan; Tan, Li; Quan, Zewei
    Chemical Society Reviews (2020), 49 (16), 6002-6038CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
    A review. Self-assembly of colloidal nanoparticles (NPs) into superstructures offers a flexible and promising pathway to manipulate the nanometer-sized particles and thus make full use of their unique properties. This bottom-up strategy builds a bridge between the NP regime and a new class of transformative materials across multiple length scales for technol. applications. In this field, anisotropic NPs with size- and shape-dependent phys. properties as self-assembly building blocks have long fascinated scientists. Self-assembly of anisotropic NPs not only opens up exciting opportunities to engineer a variety of intriguing and complex superlattice architectures, but also provides access to discover emergent collective properties that stem from their ordered arrangement. Thus, this has stimulated enormous research interests in both fundamental science and technol. applications. This present review comprehensively summarizes the latest advances in this area, and highlights their rich packing behaviors from the viewpoint of NP shape. We provide the basics of the exptl. techniques to produce NP superstructures and structural characterization tools, and detail the delicate assembled structures. Then the current understanding of the assembly dynamics is discussed with the assistance of in situ studies, followed by emergent collective properties from these NP assemblies. Finally, we end this article with the remaining challenges and outlook, hoping to encourage further research in this field.
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    Lagzi, I.; Kowalczyk, B.; Grzybowski, B. A. Liesegang Rings Engineered from Charged Nanoparticles. J. Am. Chem. Soc. 2010, 132 (1), 58– 60,  DOI: 10.1021/ja906890v
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    Liesegang Rings Engineered from Charged Nanoparticles
    Lagzi, Istvan; Kowalczyk, Bartlomiej; Grzybowski, Bartosz A.
    Journal of the American Chemical Society (2010), 132 (1), 58-60CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Functionalized nanoparticles (NPs) serve as building blocks of self-organizing chem. patterns comprising periodic zones of nanoparticle pptn. In contrast to ions, which underlie most pattern-forming chem. systems and whose properties cannot be readily modified, NPs allow for flexible adjustment of particle charges and/or material properties. In particular, changes in the particle charges control the pptn. behavior and ultimately the morphologies of the emerging patterns. The phenomenon of NP-based periodic pptn. is explained by reaction-diffusion modeling and can be used for the fractionation of NPs of different sizes.
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    Nabika, H.; Itatani, M.; Lagzi, I. Pattern Formation in Precipitation Reactions: The Liesegang Phenomenon. Langmuir 2020, 36 (2), 481– 497,  DOI: 10.1021/acs.langmuir.9b03018
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    Pattern Formation in Precipitation Reactions: The Liesegang Phenomenon
    Nabika, Hideki; Itatani, Masaki; Lagzi, Istvan
    Langmuir (2020), 36 (2), 481-497CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
    A review. Pattern formation is a frequent phenomenon in physics, chem., biol. and material science. Bottom-up pattern formation occurs usually in the interaction of the transport phenomena of chem. species with their chem. reaction. The oldest pattern formation is the Liesegang phenomenon (or periodic pptn.), which was discovered and described by Raphael Edward Liesegang in 1896, who was a German chemist and photographer, and he was born 150 years ago. The purpose of this review is to provide a comprehensive overview of this type of pattern formation. Liesegang banding occurs due to the coupling of the diffusion process of the reagents to their chem. reactions in solid hydrogels. We will discuss several phenomena obsd. and discovered in the past century including reverse patterns, pptn. patterns with dissoln. (due to complex formation), helicoidal patterns, and pptn. waves. Addnl., we will review all existing models of the Liesegang phenomenon including pre- and post-nucleation scenarios. Finally, we will highlight several applications of periodic pptn.
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    Binsbergen, F. L. Heterogeneous Nucleation of Crystallization. Prog. Solid State Chem. 1973, 8, 189– 238,  DOI: 10.1016/0079-6786(73)90007-1
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    Heterogeneous nucleation of crystallization
    Binsbergen, F. L.
    Progress in Solid State Chemistry (1973), 8 (), 189-238CODEN: PSSTAW; ISSN:0079-6786.
    A review with 195 refs. on types, causes and inhibition of nucleation, theory of heterogeneous nucleation, and exptl. observations and measurements.
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    Erdemir, D.; Lee, A. Y.; Myerson, A. S. Nucleation of Crystals from Solution: Classical and Two-Step Models. Acc. Chem. Res. 2009, 42 (5), 621– 629,  DOI: 10.1021/ar800217x
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    Nucleation of Crystals from Solution: Classical and Two-Step Models
    Erdemir, Deniz; Lee, Alfred Y.; Myerson, Allan S.
    Accounts of Chemical Research (2009), 42 (5), 621-629CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
    A review. Crystn. is vital to many processes occurring in nature and in the chem., pharmaceutical, and food industries. Notably, crystn. is an attractive isolation step for manufg. because this single process combines both particle formation and purifn. Almost all of the products based on fine chems., such as dyes, explosives, and photog. materials, require crystn. in their manuf., and more than 90% of all pharmaceutical products contain bioactive drug substances and excipients in the cryst. solid state. Hence control over the crystn. process allows manufacturers to obtain products with desired and reproducible properties. We judge the quality of a cryst. product based on four main properties: size, purity, morphol., and crystal structure. The pharmaceutical industry in particular requires prodn. of the desired crystal form (polymorph) to assure the bioavailability and stability of the drug substance. In soln. crystn., nucleation plays a decisive role in detg. the crystal structure and size distribution. Therefore, understanding the fundamentals of nucleation is crucial to achieve control over these properties. Because of its anal. simplicity, researchers have widely applied classical nucleation theory to soln. crystn. However, a no. of differences between theor. predictions and exptl. results suggest that nucleation of solids from soln. does not proceed via the classical pathway but follows more complex routes. In this Account, we discuss the shortcomings of classical nucleation theory and review studies contributing to the development of the modern two-step model. In the two-step model that was initially proposed for protein crystn., a sufficient-sized cluster of solute mols. forms first, followed by reorganization of that cluster into an ordered structure. In recent exptl. and theor. studies, we and other researchers have demonstrated the applicability of the two-step mechanism to both macromols. and small org. mols., suggesting that this mechanism may underlie most crystn. processes from solns. Because we have obsd. an increase in the organization time of appropriate lattice structures with greater mol. complexity, we propose that organization is the rate-detg. step. Further development of a clearer picture of nucleation may help det. the optimum conditions necessary for the effective organization within the clusters. In addn., greater understanding of these processes may lead to the design of auxiliaries that can increase the rate of nucleation and avoid the formation of undesired solid forms, allowing researchers to obtain the final product in a timely and reproducible manner.
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    Nakamuro, T.; Sakakibara, M.; Nada, H.; Harano, K.; Nakamura, E. Capturing the Moment of Emergence of Crystal Nucleus from Disorder. J. Am. Chem. Soc. 2021, 143 (4), 1763– 1767,  DOI: 10.1021/jacs.0c12100
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    Capturing the Moment of Emergence of Crystal Nucleus from Disorder
    Nakamuro, Takayuki; Sakakibara, Masaya; Nada, Hiroki; Harano, Koji; Nakamura, Eiichi
    Journal of the American Chemical Society (2021), 143 (4), 1763-1767CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Crystn. is the process of atoms or mols. forming an organized solid via nucleation and growth. Being intrinsically stochastic, the research at an atomistic level was a huge exptl. challenge. In situ detection is reported of a crystal nucleus forming during nucleation/growth of a NaCl nanocrystal, as video recorded in the interior of a vibrating conical C nanotube at 20-40 ms/frame with localization precision of <0.1 nm. NaCl units were seen assembled to form a cluster fluctuating between featureless and semiordered states, which suddenly formed a crystal. Subsequent crystal growth at 298 K and shrinkage at 473 K took place also in a stochastic manner. Productive contributions of the graphitic surface and its mech. vibration were exptl. indicated.
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    Kalsin, A. M.; Kowalczyk, B.; Smoukov, S. K.; Klajn, R.; Grzybowski, B. A. Ionic-like Behavior of Oppositely Charged Nanoparticles. J. Am. Chem. Soc. 2006, 128 (47), 15046– 15047,  DOI: 10.1021/ja0642966
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    Ionic-like Behavior of Oppositely Charged Nanoparticles
    Kalsin, Alexander M.; Kowalczyk, Bartlomiej; Smoukov, Stoyan K.; Klajn, Rafal; Grzybowski, Bartosz A.
    Journal of the American Chemical Society (2006), 128 (47), 15046-15047CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Mixts. of oppositely charged nanoparticles of various sizes and charge ratios ppt. only at the point of electroneutrality. This phenomenon -specific to the nanoscale and reminiscent of threshold pptn. of ions- is a consequence of the formation of core-and-shell nanoparticle aggregates, in which the shells are composed of like-charged particles and are stabilized by efficient electrostatic screening.
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    Kalsin, A. M.; Kowalczyk, B.; Wesson, P.; Paszewski, M.; Grzybowski, B. A. Studying the Thermodynamics of Surface Reactions on Nanoparticles by Electrostatic Titrations. J. Am. Chem. Soc. 2007, 129 (21), 6664– 6665,  DOI: 10.1021/ja068329t
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    Studying the Thermodynamics of Surface Reactions on Nanoparticles by Electrostatic Titrations
    Kalsin, Alexander M.; Kowalczyk, Bartlomiej; Wesson, Paul; Paszewski, Maciej; Grzybowski, Bartosz A.
    Journal of the American Chemical Society (2007), 129 (21), 6664-6665CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    For nanoparticles coated with binary self-assembled monolayers (m-SAM) contg. charged or ionizable mols., the relative equil. consts. and the difference in the free energies of absorption of the m-SAM's components can be obtained in a straightforward way by titrating such nanoparticles with oppositely charged nanoparticle "stds." until pptn. at the point of overall electro-neutrality.
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    Bishop, K. J. M.; Grzybowski, B. A. Nanoions”: Fundamental Properties and Analytical Applications of Charged Nanoparticles. ChemPhysChem 2007, 8 (15), 2171– 2176,  DOI: 10.1002/cphc.200700349
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    "Nanoions": fundamental properties and analytical applications of charged nanoparticles
    Bishop, Kyle J. M.; Grzybowski, Bartosz A.
    ChemPhysChem (2007), 8 (15), 2171-2176CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Mixts. of oppositely charged nanoparticles (NPs) ppt. sharply only at the point of NP electroneutrality. This behavior-reminiscent of the threshold pptn. of inorg. ions-is specific to the nanoscale and can be attributed to the formation of like-charged NP clusters stabilized in soln. by mutual electrostatic repulsions. NP titrns. based on this phenomenon provide a uniquely accurate tool for measuring charges tethered onto nanoscopic objects and for studying the thermodn. of surface reactions at the nanoscale.
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  • Abstract

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    Figure 1

    Figure 1. (a) TEM micrographs and (b) size distribution of the AuNPs used in the precipitation experiments of the oppositely charged NPs. (c) The precipitation process of the oppositely charged AuNPs consists of two consecutive steps: (1) aggregation of NPs into clusters manifested in a red-shift of the spectrum (due to an increase of the particle size) and an increase of the extinction (because the red-shifted mode has a larger extinction cross section) and (2) coagulation of these clusters which sediment from the solution manifested in a decrease of the extinction.

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    Figure 2

    Figure 2. (a) Photographs of the mixtures of the oppositely charged AuNPs applying various mixing ratios after 1 h, starting the experiments using (i) large, (ii) medium, and (iii) small AuNPs with the concentration of 0.56 mM (in terms of gold atoms). (b) Extinction of oppositely charged AuNP mixtures at various mixing ratios after 1 h starting the experiments using AuNPs with the concentration of (b) 0.56 mM and (c) 0.26 mM (measured at λ = 523 nm). The red, green, and blue colors correspond to the small, medium, and large NPs, respectively.

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    Figure 3

    Figure 3. Dependence of (a) the hydrodynamic size (measured by DLS and calculated as an average of the population) and (b) the zeta potential of the clusters formed in the interaction of the oppositely charged NPs on the mixing ratio (χ). The red, green, and blue colors correspond to the small, medium, and large NPs, respectively. The concentration of the solutions of oppositely charged AuNPs was 0.75 mM.

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    Figure 4

    Figure 4. Time-dependent parameters of the medium-sized (4.6 nm) system corresponding to compositions inside (χ = 0.6) and outside (χ = 0.7) of the sedimentation window. The intensity size distribution showing the inside case (a) and overall count rates (b) have been obtained from dynamic light scattering measurements, while the plasmon peak position shift (c) and extinction measured at 400 nm have been extracted from the optical spectra (d).

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    Figure 5

    Figure 5. Results of the equilibrium model simulations on the precipitation window using smaller (r = 1) and larger (r = 5) oppositely charged NPs. The red color corresponds to the size of the clusters that reach the critical size (Rc = 100) and sediment from the solution. nmax is the highest initial number of like charged AuNPs.

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      Rao, Anish; Roy, Sumit; Jain, Vanshika; Pillai, Pramod P.
      ACS Applied Materials & Interfaces (2023), 15 (21), 25248-25274CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      A review. The creation of matter with varying degrees of complexities and desired functions is one of the ultimate targets of self-assembly. The ability to regulate the complex interactions between the individual components is essential in achieving this target. In this direction, the initial success of controlling the pathways and final thermodn. states of a self-assembly process is promising. Despite the progress made in the field, there has been a growing interest in pushing the limits of self-assembly processes. The main inception of this interest is that the intended self-assembled state, with varying complexities, may not be "at equil. (or at global min.)", rendering free energy minimization unsuitable to form the desired product. Thus, we believe that a thorough understanding of the design principles as well as the ability to predict the outcome of a self-assembly process is essential to form a collection of the next generation of complex matter. The present review highlights the potent role of finely tuned interparticle interactions in nanomaterials to achieve the preferred self-assembled structures with the desired properties. We believe that bringing the design and prediction to nanoparticle self-assembly processes will have a similar effect as retrosynthesis had on the logic of chem. synthesis. Along with the guiding principles, the review gives a summary of the different types of products created from nanoparticle assemblies and the functional properties emerging from them. Finally, we highlight the reasonable expectations from the field and the challenges lying ahead in the creation of complex and evolvable matter.
    6. 6
      Huang, C.; Chen, X.; Xue, Z.; Wang, T. Effect of Structure: A New Insight into Nanoparticle Assemblies from Inanimate to Animate. Sci. Adv. 2020, 6 (20), eaba1321  DOI: 10.1126/sciadv.aba1321
      There is no corresponding record for this reference.
    7. 7
      Gu, Z.; Atherton, J. J.; Xu, Z. P. Hierarchical Layered Double Hydroxide Nanocomposites: Structure, Synthesis and Applications. Chem. Commun. 2015, 51 (15), 3024– 3036,  DOI: 10.1039/C4CC07715F
      7
      Hierarchical layered double hydroxide nanocomposites: structure, synthesis and applications
      Gu, Zi; Atherton, John James; Xu, Zhi Ping
      Chemical Communications (Cambridge, United Kingdom) (2015), 51 (15), 3024-3036CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      A review. Layered double hydroxide (LDH)-based nanocomposites, constructed by interacting LDH nanoparticles with other nanomaterials (e.g. silica nanoparticles and magnetic nanoparticles) or polymeric mols. (e.g. proteins), are an emerging yet active area in healthcare, environmental remediation, energy conversion and storage. Combining advantages of each component in the structure and functions, hierarchical LDH-based nanocomposites showed great potential in biomedicine, water purifn., and energy storage and conversion. This feature article summarizes the recent advances in LDH-based nanocomposites, focusing on their synthesis, structure, and application in drug delivery, bio-imaging, water purifn., supercapacitors, and catalysis.
    8. 8
      Grötsch, R. K.; Wanzke, C.; Speckbacher, M.; Angı, A.; Rieger, B.; Boekhoven, J. Pathway Dependence in the Fuel-Driven Dissipative Self-Assembly of Nanoparticles. J. Am. Chem. Soc. 2019, 141 (25), 9872– 9878,  DOI: 10.1021/jacs.9b02004
      8
      Pathway Dependence in the Fuel-Driven Dissipative Self-Assembly of Nanoparticles
      Grotsch Raphael K; Wanzke Caren; Boekhoven Job; Speckbacher Maximilian; Angi Arzu; Rieger Bernhard
      Journal of the American Chemical Society (2019), 141 (25), 9872-9878 ISSN:.
      We describe the self-assembly of gold and iron oxide nanoparticles regulated by a chemical reaction cycle that hydrolyzes a carbodiimide-based fuel. In a reaction with the chemical fuel, the nanoparticles are chemically activated to a state that favors assembling into clusters. The activated state is metastable and decays to the original precursor reversing the assembly. The dynamic interplay of activation and deactivation results in a material of which the behavior is regulated by the amount of fuel added to the system; they either did not assemble, assembled transiently, or assembled permanently in kinetically trapped clusters. Because of the irreversibility of the kinetically trapped clusters, we found that the behavior of the self-assembly was prone to hysteresis effects. The final state of the system in the energy landscape depended on the pathway of preparation. For example, when a large amount of fuel was added at once, the material would end up kinetically trapped in a local minimum. When the same amount of fuel was added in small batches with sufficient time for the system to re-equilibrate, the final state would be the global minimum. A better understanding of pathway complexity in the energy landscape is crucial for the development of fuel-driven supramolecular materials.
    9. 9
      van Ravensteijn, B. G. P.; Voets, I. K.; Kegel, W. K.; Eelkema, R. Out-of-Equilibrium Colloidal Assembly Driven by Chemical Reaction Networks. Langmuir 2020, 36 (36), 10639– 10656,  DOI: 10.1021/acs.langmuir.0c01763
      9
      Out-of-Equilibrium Colloidal Assembly Driven by Chemical Reaction Networks
      van Ravensteijn, Bas G. P.; Voets, Ilja K.; Kegel, Willem K.; Eelkema, Rienk
      Langmuir (2020), 36 (36), 10639-10656CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      A review. Transient assembled structures play an indispensable role in a wide variety of processes fundamental to living organisms including cellular transport, cell motility, and proliferation. Typically, the formation of these transient structures is driven by the consumption of mol. fuels via dissipative reaction networks. In these networks, building blocks are converted from inactive precursor states to active (assembling) states by (a set of) irreversible chem. reactions. Since the activated state is intrinsically unstable and can be maintained only in the presence of sufficient fuel, fuel depletion results in the spontaneous disintegration of the formed superstructures. Consequently, the properties and behavior of these assembled structures are governed by the kinetics of fuel consumption rather than by their thermodn. stability. This fuel dependency endows biol. systems with unprecedented spatiotemporal adaptability and inherent self-healing capabilities. Fascinated by these unique material characteristics, coupling the assembly behavior to mol. fuel or light-driven reaction networks was recently implemented in synthetic (supra)mol. systems. In this invited feature article, we discuss recent studies demonstrating that dissipative assembly is not limited to the mol. world but can also be translated to building blocks of colloidal dimensions. We highlight crucial guiding principles for the successful design of dissipative colloidal systems and illustrate these with the current state of the art. Finally, we present our vision on the future of the field and how marrying nonequil. self-assembly with the functional properties assocd. with colloidal building blocks presents a promising route for the development of next-generation materials.
    10. 10
      Bishop, K. J. M.; Wilmer, C. E.; Soh, S.; Grzybowski, B. A. Nanoscale Forces and Their Uses in Self-Assembly. Small 2009, 5 (14), 1600– 1630,  DOI: 10.1002/smll.200900358
      10
      Nanoscale forces and their uses in self-assembly
      Bishop, Kyle J. M.; Wilmer, Christopher E.; Soh, Siowling; Grzybowski, Bartosz A.
      Small (2009), 5 (14), 1600-1630CODEN: SMALBC; ISSN:1613-6810. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. The ability to assemble nanoscopic components into larger structures and materials depends crucially on the ability to understand in quant. detail and subsequently "engineer" the interparticle interactions. This Review provides a crit. examn. of the various interparticle forces (van der Waals, electrostatic, magnetic, mol., and entropic) that can be used in nanoscale self-assembly. For each type of interaction, the magnitude and the length scale are discussed, as well as the scaling with particle size and interparticle distance. In all cases, the discussion emphasizes characteristics unique to the nanoscale. These theor. considerations are accompanied by examples of recent exptl. systems, in which specific interaction types were used to drive nanoscopic self-assembly. Overall, this Review aims to provide a comprehensive yet easily accessible resource of nanoscale-specific interparticle forces that can be implemented in models or simulations of self-assembly processes at this scale.
    11. 11
      Luo, Y.; Zhao, R.; Pendry, J. B. Van Der Waals Interactions at the Nanoscale: The Effects of Nonlocality. Proc. Natl. Acad. Sci. U. S. A. 2014, 111 (52), 18422– 18427,  DOI: 10.1073/pnas.1420551111
      11
      Van der Waals interactions at the nanoscale: The effects of nonlocality
      Luo, Yu; Zhao, Rongkuo; Pendry, John B.
      Proceedings of the National Academy of Sciences of the United States of America (2014), 111 (52), 18422-18427CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      Calcd. using classical electromagnetism, the van der Waals force increases without limit as two surfaces approach. In reality, the force sats. because the electrons cannot respond to fields of very short wavelength: polarization charges are always smeared out to some degree and in consequence the response is nonlocal. Nonlocality also plays an important role in the optical spectrum and distribution of the modes but introduces complexity into calcns., hindering an anal. soln. for interactions at the nanometer scale. Here, taking as an example the case of two touching nanospheres, the authors show for the 1st time, to the authors' knowledge, that nonlocality in 3-dimensional plasmonic systems can be accurately analyzed using the transformation optics approach. The effects of nonlocality dramatically weaken the field enhancement between the spheres and hence the van der Waals interaction and to modify the spectral shifts of plasmon modes.
    12. 12
      Walker, D. A.; Kowalczyk, B.; de la Cruz, M. O.; Grzybowski, B. A. Electrostatics at the Nanoscale. Nanoscale 2011, 3 (4), 1316– 1344,  DOI: 10.1039/C0NR00698J
      12
      Electrostatics at the nanoscale
      Walker, David A.; Kowalczyk, Bartlomiej; Olvera de la Cruz, Monica; Grzybowski, Bartosz A.
      Nanoscale (2011), 3 (4), 1316-1344CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
      A review. Electrostatic forces are amongst the most versatile interactions to mediate the assembly of nanostructured materials. Depending on exptl. conditions, these forces can be long- or short-ranged, can be either attractive or repulsive, and their directionality can be controlled by the shapes of the charged nano-objects. This Review is intended to serve as a primer for experimentalists curious about the fundamentals of nanoscale electrostatics and for theorists wishing to learn about recent exptl. advances in the field. Accordingly, the first portion introduces the theor. models of electrostatic double layers and derives electrostatic interaction potentials applicable to particles of different sizes and/or shapes and under different exptl. conditions. This discussion is followed by the review of the key exptl. systems in which electrostatic interactions are operative. Examples include electroactive and "switchable" nanoparticles, mixts. of charged nanoparticles, nanoparticle chains, sheets, coatings, crystals, and crystals-within-crystals. Applications of these and other structures in chem. sensing and amplification are also illustrated.
    13. 13
      Ambrosetti, A.; Subashchandrabose, S.; Liu, B.; Silvestrelli, P. L. Tunable van Der Waals Interactions in Low-Dimensional Nanostructures. J. Chem. Phys. 2021, 154 (22), 224105,  DOI: 10.1063/5.0051235
      13
      Tunable van der Waals interactions in low-dimensional nanostructures
      Ambrosetti, Alberto; Subashchandrabose, S.; Liu, B.; Silvestrelli, Pier Luigi
      Journal of Chemical Physics (2021), 154 (22), 224105CODEN: JCPSA6; ISSN:0021-9606. (American Institute of Physics)
      Non-covalent van der Waals interactions play a major role at the nanoscale, and even a slight change in their asymptotic decay could produce a major impact on surface phenomena, self-assembly of nanomaterials, and biol. systems. By a full many-body description of vdW interactions in coupled carbyne-like chains and graphenic structures, here, we demonstrate that both modulus and a range of interfragment forces can be effectively tuned, introducing mech. strain and doping (or polarizability change). This result contrasts with conventional pairwise vdW predictions, where the two-body approxn. essentially fixes the asymptotic decay of interfragment forces. The present results provide viable pathways for detailed exptl. control of nanoscale systems that could be exploited both in static geometrical configurations and in dynamical processes. (c) 2021 American Institute of Physics.
    14. 14
      Xu, Q.; Zhao, X. Electrostatic Interactions versus van Der Waals Interactions in the Self-Assembly of Dispersed Nanodiamonds. J. Mater. Chem. 2012, 22 (32), 16416– 16421,  DOI: 10.1039/c2jm32918b
      14
      Electrostatic interactions versus van der Waals interactions in the self-assembly of dispersed nanodiamonds
      Xu, Qian; Zhao, Xiang
      Journal of Materials Chemistry (2012), 22 (32), 16416-16421CODEN: JMACEP; ISSN:0959-9428. (Royal Society of Chemistry)
      4-5 Nm nanodiamonds tend to self-assemble into 100-200 nm nanodiamond aggregations and furthermore nanodiamonds in the early stages of the detonation process present fantastic twinned morphologies, indicating that there are strong interactions among these nanodiamonds. Herein, electrostatic interactions and van der Waals interactions between two nanodiamonds are explored using DFT computations in conjunction with Monte Carlo mol. simulations. It is indicated that the van der Waals forces are much stronger than the electrostatic forces for the unsatd. nanodiamonds. More importantly, two assembly features are exposed as follows: assembly has a preferential face-to-face orientation; assembly has a strong binding energy comparable to the dissocn. energy of C-C bonding, which is -116.1 kcal mol-1 for a 2.48 nm truncated octahedral nanodiamond. The results suggest that the strong forces holding the nanodiamond aggregation almost certainly attribute to the proposed strong van der Waals forces, which is of great importance in understanding the aggregative properties of nanodiamond.
    15. 15
      Li, Y.; Li, H.; He, X. Self-Assembly of Binary Particles with Electrostatic and van Der Waals Interactions. Chin. J. Chem. Phys. 2014, 27 (4), 419– 427,  DOI: 10.1063/1674-0068/27/04/419-427
      15
      Self-assembly of Binary Particles with Electrostatic and van der Waals Interactions
      Li, Yan; Li, Hua-ping; He, Xue-hao
      Chinese Journal of Chemical Physics (2014), 27 (4), 419-427CODEN: CJCPA6; ISSN:1674-0068. (Chinese Physical Society)
      Nanoparticles with competitive interactions in soln. can aggregate into complex structures. In this work, the synergistic self-assembles of binary particles with electrostatic and van der Waals interactions are studied with the particle Langevin dynamics simulation using a simple coarse-grained particle model. Various aggregations such as spherical, stacking-disk and tube structures are obsd. by varying the particles size and the interaction strength. The aggregation structures are explained with the packing theories of amphiphilic mols. in soln. and diblock copolymers in bulk. When the opposite ions are introduced into soln., the distribution of structures in the phase diagram appears an obvious offset. The simulation result is helpful to deeply understand the formation mechanism of complex nanostructures of multicomponent particles in soln.
    16. 16
      Bian, T.; Gardin, A.; Gemen, J.; Houben, L.; Perego, C.; Lee, B.; Elad, N.; Chu, Z.; Pavan, G. M.; Klajn, R. Electrostatic Co-Assembly of Nanoparticles with Oppositely Charged Small Molecules into Static and Dynamic Superstructures. Nat. Chem. 2021, 13 (10), 940– 949,  DOI: 10.1038/s41557-021-00752-9
      16
      Electrostatic co-assembly of nanoparticles with oppositely charged small molecules into static and dynamic superstructures
      Bian, Tong; Gardin, Andrea; Gemen, Julius; Houben, Lothar; Perego, Claudio; Lee, Byeongdu; Elad, Nadav; Chu, Zonglin; Pavan, Giovanni M.; Klajn, Rafal
      Nature Chemistry (2021), 13 (10), 940-949CODEN: NCAHBB; ISSN:1755-4330. (Nature Portfolio)
      Coulombic interactions can be used to assemble charged nanoparticles into higher-order structures, but the process requires oppositely charged partners that are similarly sized. The ability to mediate the assembly of such charged nanoparticles using structurally simple small mols. would greatly facilitate the fabrication of nanostructured materials and harnessing their applications in catalysis, sensing and photonics. Here we show that small mols. with as few as three elec. charges can effectively induce attractive interactions between oppositely charged nanoparticles in water. These interactions can guide the assembly of charged nanoparticles into colloidal crystals of a quality previously only thought to result from their co-crystn. with oppositely charged nanoparticles of a similar size. Transient nanoparticle assemblies can be generated using pos. charged nanoparticles and multiply charged anions that are enzymically hydrolyzed into mono- and/or dianions. Our findings demonstrate an approach for the facile fabrication, manipulation and further investigation of static and dynamic nanostructured materials in aq. environments.
    17. 17
      Grzelczak, M.; Liz-Marzán, L. M.; Klajn, R. Stimuli-Responsive Self-Assembly of Nanoparticles. Chem. Soc. Rev. 2019, 48 (5), 1342– 1361,  DOI: 10.1039/C8CS00787J
      17
      Stimuli-responsive self-assembly of nanoparticles
      Grzelczak, Marek; Liz-Marzan, Luis M.; Klajn, Rafal
      Chemical Society Reviews (2019), 48 (5), 1342-1361CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      The capacity to respond or adapt to environmental changes is an intrinsic property of living systems that comprise highly-connected subcomponents communicating through chem. networks. The development of responsive synthetic systems is a relatively new research area that covers different disciplines, among which nanochem. brings conceptually new demonstrations. Esp. attractive are ligand-protected gold nanoparticles, which have been extensively used over the last decade as building blocks in constructing superlattices or dynamic aggregates, under the effect of an applied stimulus. To reflect the importance of surface chem. and nanoparticle core compn. in the dynamic self-assembly of nanoparticles, we provide here an overview of various available stimuli, as tools for synthetic chemists to exploit. Along with this task, the review starts with the use of chem. stimuli such as solvent, pH, gases, metal ions or biomols. It then focuses on phys. stimuli: temp., magnetic and elec. fields, as well as light. To reflect on the increasing complexity of current architectures, we discuss systems that are responsive to more than one stimulus, to finally encourage further research by proposing future challenges.
    18. 18
      Deng, K.; Luo, Z.; Tan, L.; Quan, Z. Self-Assembly of Anisotropic Nanoparticles into Functional Superstructures. Chem. Soc. Rev. 2020, 49 (16), 6002– 6038,  DOI: 10.1039/D0CS00541J
      18
      Self-assembly of anisotropic nanoparticles into functional superstructures
      Deng, Kerong; Luo, Zhishan; Tan, Li; Quan, Zewei
      Chemical Society Reviews (2020), 49 (16), 6002-6038CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. Self-assembly of colloidal nanoparticles (NPs) into superstructures offers a flexible and promising pathway to manipulate the nanometer-sized particles and thus make full use of their unique properties. This bottom-up strategy builds a bridge between the NP regime and a new class of transformative materials across multiple length scales for technol. applications. In this field, anisotropic NPs with size- and shape-dependent phys. properties as self-assembly building blocks have long fascinated scientists. Self-assembly of anisotropic NPs not only opens up exciting opportunities to engineer a variety of intriguing and complex superlattice architectures, but also provides access to discover emergent collective properties that stem from their ordered arrangement. Thus, this has stimulated enormous research interests in both fundamental science and technol. applications. This present review comprehensively summarizes the latest advances in this area, and highlights their rich packing behaviors from the viewpoint of NP shape. We provide the basics of the exptl. techniques to produce NP superstructures and structural characterization tools, and detail the delicate assembled structures. Then the current understanding of the assembly dynamics is discussed with the assistance of in situ studies, followed by emergent collective properties from these NP assemblies. Finally, we end this article with the remaining challenges and outlook, hoping to encourage further research in this field.
    19. 19
      Lagzi, I.; Kowalczyk, B.; Grzybowski, B. A. Liesegang Rings Engineered from Charged Nanoparticles. J. Am. Chem. Soc. 2010, 132 (1), 58– 60,  DOI: 10.1021/ja906890v
      19
      Liesegang Rings Engineered from Charged Nanoparticles
      Lagzi, Istvan; Kowalczyk, Bartlomiej; Grzybowski, Bartosz A.
      Journal of the American Chemical Society (2010), 132 (1), 58-60CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Functionalized nanoparticles (NPs) serve as building blocks of self-organizing chem. patterns comprising periodic zones of nanoparticle pptn. In contrast to ions, which underlie most pattern-forming chem. systems and whose properties cannot be readily modified, NPs allow for flexible adjustment of particle charges and/or material properties. In particular, changes in the particle charges control the pptn. behavior and ultimately the morphologies of the emerging patterns. The phenomenon of NP-based periodic pptn. is explained by reaction-diffusion modeling and can be used for the fractionation of NPs of different sizes.
    20. 20
      Nabika, H.; Itatani, M.; Lagzi, I. Pattern Formation in Precipitation Reactions: The Liesegang Phenomenon. Langmuir 2020, 36 (2), 481– 497,  DOI: 10.1021/acs.langmuir.9b03018
      20
      Pattern Formation in Precipitation Reactions: The Liesegang Phenomenon
      Nabika, Hideki; Itatani, Masaki; Lagzi, Istvan
      Langmuir (2020), 36 (2), 481-497CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      A review. Pattern formation is a frequent phenomenon in physics, chem., biol. and material science. Bottom-up pattern formation occurs usually in the interaction of the transport phenomena of chem. species with their chem. reaction. The oldest pattern formation is the Liesegang phenomenon (or periodic pptn.), which was discovered and described by Raphael Edward Liesegang in 1896, who was a German chemist and photographer, and he was born 150 years ago. The purpose of this review is to provide a comprehensive overview of this type of pattern formation. Liesegang banding occurs due to the coupling of the diffusion process of the reagents to their chem. reactions in solid hydrogels. We will discuss several phenomena obsd. and discovered in the past century including reverse patterns, pptn. patterns with dissoln. (due to complex formation), helicoidal patterns, and pptn. waves. Addnl., we will review all existing models of the Liesegang phenomenon including pre- and post-nucleation scenarios. Finally, we will highlight several applications of periodic pptn.
    21. 21
      Binsbergen, F. L. Heterogeneous Nucleation of Crystallization. Prog. Solid State Chem. 1973, 8, 189– 238,  DOI: 10.1016/0079-6786(73)90007-1
      21
      Heterogeneous nucleation of crystallization
      Binsbergen, F. L.
      Progress in Solid State Chemistry (1973), 8 (), 189-238CODEN: PSSTAW; ISSN:0079-6786.
      A review with 195 refs. on types, causes and inhibition of nucleation, theory of heterogeneous nucleation, and exptl. observations and measurements.
    22. 22
      Erdemir, D.; Lee, A. Y.; Myerson, A. S. Nucleation of Crystals from Solution: Classical and Two-Step Models. Acc. Chem. Res. 2009, 42 (5), 621– 629,  DOI: 10.1021/ar800217x
      22
      Nucleation of Crystals from Solution: Classical and Two-Step Models
      Erdemir, Deniz; Lee, Alfred Y.; Myerson, Allan S.
      Accounts of Chemical Research (2009), 42 (5), 621-629CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
      A review. Crystn. is vital to many processes occurring in nature and in the chem., pharmaceutical, and food industries. Notably, crystn. is an attractive isolation step for manufg. because this single process combines both particle formation and purifn. Almost all of the products based on fine chems., such as dyes, explosives, and photog. materials, require crystn. in their manuf., and more than 90% of all pharmaceutical products contain bioactive drug substances and excipients in the cryst. solid state. Hence control over the crystn. process allows manufacturers to obtain products with desired and reproducible properties. We judge the quality of a cryst. product based on four main properties: size, purity, morphol., and crystal structure. The pharmaceutical industry in particular requires prodn. of the desired crystal form (polymorph) to assure the bioavailability and stability of the drug substance. In soln. crystn., nucleation plays a decisive role in detg. the crystal structure and size distribution. Therefore, understanding the fundamentals of nucleation is crucial to achieve control over these properties. Because of its anal. simplicity, researchers have widely applied classical nucleation theory to soln. crystn. However, a no. of differences between theor. predictions and exptl. results suggest that nucleation of solids from soln. does not proceed via the classical pathway but follows more complex routes. In this Account, we discuss the shortcomings of classical nucleation theory and review studies contributing to the development of the modern two-step model. In the two-step model that was initially proposed for protein crystn., a sufficient-sized cluster of solute mols. forms first, followed by reorganization of that cluster into an ordered structure. In recent exptl. and theor. studies, we and other researchers have demonstrated the applicability of the two-step mechanism to both macromols. and small org. mols., suggesting that this mechanism may underlie most crystn. processes from solns. Because we have obsd. an increase in the organization time of appropriate lattice structures with greater mol. complexity, we propose that organization is the rate-detg. step. Further development of a clearer picture of nucleation may help det. the optimum conditions necessary for the effective organization within the clusters. In addn., greater understanding of these processes may lead to the design of auxiliaries that can increase the rate of nucleation and avoid the formation of undesired solid forms, allowing researchers to obtain the final product in a timely and reproducible manner.
    23. 23
      Nakamuro, T.; Sakakibara, M.; Nada, H.; Harano, K.; Nakamura, E. Capturing the Moment of Emergence of Crystal Nucleus from Disorder. J. Am. Chem. Soc. 2021, 143 (4), 1763– 1767,  DOI: 10.1021/jacs.0c12100
      23
      Capturing the Moment of Emergence of Crystal Nucleus from Disorder
      Nakamuro, Takayuki; Sakakibara, Masaya; Nada, Hiroki; Harano, Koji; Nakamura, Eiichi
      Journal of the American Chemical Society (2021), 143 (4), 1763-1767CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Crystn. is the process of atoms or mols. forming an organized solid via nucleation and growth. Being intrinsically stochastic, the research at an atomistic level was a huge exptl. challenge. In situ detection is reported of a crystal nucleus forming during nucleation/growth of a NaCl nanocrystal, as video recorded in the interior of a vibrating conical C nanotube at 20-40 ms/frame with localization precision of <0.1 nm. NaCl units were seen assembled to form a cluster fluctuating between featureless and semiordered states, which suddenly formed a crystal. Subsequent crystal growth at 298 K and shrinkage at 473 K took place also in a stochastic manner. Productive contributions of the graphitic surface and its mech. vibration were exptl. indicated.
    24. 24
      Kalsin, A. M.; Kowalczyk, B.; Smoukov, S. K.; Klajn, R.; Grzybowski, B. A. Ionic-like Behavior of Oppositely Charged Nanoparticles. J. Am. Chem. Soc. 2006, 128 (47), 15046– 15047,  DOI: 10.1021/ja0642966
      24
      Ionic-like Behavior of Oppositely Charged Nanoparticles
      Kalsin, Alexander M.; Kowalczyk, Bartlomiej; Smoukov, Stoyan K.; Klajn, Rafal; Grzybowski, Bartosz A.
      Journal of the American Chemical Society (2006), 128 (47), 15046-15047CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Mixts. of oppositely charged nanoparticles of various sizes and charge ratios ppt. only at the point of electroneutrality. This phenomenon -specific to the nanoscale and reminiscent of threshold pptn. of ions- is a consequence of the formation of core-and-shell nanoparticle aggregates, in which the shells are composed of like-charged particles and are stabilized by efficient electrostatic screening.
    25. 25
      Kalsin, A. M.; Kowalczyk, B.; Wesson, P.; Paszewski, M.; Grzybowski, B. A. Studying the Thermodynamics of Surface Reactions on Nanoparticles by Electrostatic Titrations. J. Am. Chem. Soc. 2007, 129 (21), 6664– 6665,  DOI: 10.1021/ja068329t
      25
      Studying the Thermodynamics of Surface Reactions on Nanoparticles by Electrostatic Titrations
      Kalsin, Alexander M.; Kowalczyk, Bartlomiej; Wesson, Paul; Paszewski, Maciej; Grzybowski, Bartosz A.
      Journal of the American Chemical Society (2007), 129 (21), 6664-6665CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      For nanoparticles coated with binary self-assembled monolayers (m-SAM) contg. charged or ionizable mols., the relative equil. consts. and the difference in the free energies of absorption of the m-SAM's components can be obtained in a straightforward way by titrating such nanoparticles with oppositely charged nanoparticle "stds." until pptn. at the point of overall electro-neutrality.
    26. 26
      Bishop, K. J. M.; Grzybowski, B. A. Nanoions”: Fundamental Properties and Analytical Applications of Charged Nanoparticles. ChemPhysChem 2007, 8 (15), 2171– 2176,  DOI: 10.1002/cphc.200700349
      26
      "Nanoions": fundamental properties and analytical applications of charged nanoparticles
      Bishop, Kyle J. M.; Grzybowski, Bartosz A.
      ChemPhysChem (2007), 8 (15), 2171-2176CODEN: CPCHFT; ISSN:1439-4235. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Mixts. of oppositely charged nanoparticles (NPs) ppt. sharply only at the point of NP electroneutrality. This behavior-reminiscent of the threshold pptn. of inorg. ions-is specific to the nanoscale and can be attributed to the formation of like-charged NP clusters stabilized in soln. by mutual electrostatic repulsions. NP titrns. based on this phenomenon provide a uniquely accurate tool for measuring charges tethered onto nanoscopic objects and for studying the thermodn. of surface reactions at the nanoscale.
    27. 27
      Grzybowski, B. A. Charged Nanoparticles Crystallizing and Controlling Crystallization: From Coatings to Nanoparticle Surfactants to Chemical Amplifiers. CrystEngComm 2014, 16 (40), 9368– 9380,  DOI: 10.1039/C4CE00689E
      27
      Charged nanoparticles crystallizing and controlling crystallization: from coatings to nanoparticle surfactants to chemical amplifiers
      Grzybowski, Bartosz A.
      CrystEngComm (2014), 16 (40), 9368-9380CODEN: CRECF4; ISSN:1466-8033. (Royal Society of Chemistry)
      Metal nanoparticles functionalized with self-assembled monolayers of ligands terminated in charged groups constitute a unique class of nanoscopic polyions - or "nanoions" in short - capable of assembling into higher-order structures ranging from two-dimensional coatings on various types of surfaces (including chem. inert polymers as well as inorg. microcrystals) to three-dimensional nanoparticle crystals. These crystals can comprise either spherical or non-spherical nanoparticles, can feature unusual particle arrangements (e.g., diamond-like), and - after already being assembled - can be further "post-processed" to act as chem. sensors of unmatched sensitivity. This "post-processing" of the crystals involves functionalization with dithiols that bridge nearby particles but are cleavable in the presence of either small-mol. or enzyme analytes. When the dithiols are cut, the NP crystals disintegrate into tens of millions of brightly colored individual particles translating the presence of few analyte mols. into a macroscopic color change readily detectable to the naked eye. Demonstrations such as this one illustrate what we believe should be the future of nanoscale assembly - namely, synthesis of structures in which nanoscopic components enable new and useful functions.
    28. 28
      Bishop, K. J. M.; Kowalczyk, B.; Grzybowski, B. A. Precipitation of Oppositely Charged Nanoparticles by Dilution and/or Temperature Increase. J. Phys. Chem. B 2009, 113 (5), 1413– 1417,  DOI: 10.1021/jp8056493
      28
      Precipitation of Oppositely Charged Nanoparticles by Dilution and/or Temperature Increase
      Bishop, Kyle J. M.; Kowalczyk, Bartlomiej; Grzybowski, Bartosz A.
      Journal of Physical Chemistry B (2009), 113 (5), 1413-1417CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
      Mixts. of oppositely charged nanoparticles (NPs) exhibit anomalous soly. behavior and ppt. either upon diln. or upon temp. increase. Pptn. is reversible and can be explained by a thermodn. model that accounts for changes in the electrostatic interactions due to the adsorption/desorption of counterions from the surface of the NPs. Specifically, decreasing the salt concn. via diln. or increasing the temp. causes dissocn. of counterions from the NP surfaces, increasing the magnitude of electrostatic interactions between NPs and resulting in their pptn. Model predictions of NP soly. are in quant. agreement with the exptl. observations. Such predictions are of practical importance for the prepn. of patchy electrostatic coatings and ionic-like NP supracrystals.
    29. 29
      Moglianetti, M.; Ponomarev, E.; Szybowski, M.; Stellacci, F.; Reguera, J. Co-Precipitation of Oppositely Charged Nanoparticles: The Case of Mixed Ligand Nanoparticles. J. Phys. Appl. Phys. 2015, 48 (43), 434001,  DOI: 10.1088/0022-3727/48/43/434001
      There is no corresponding record for this reference.
    30. 30
      Pillai, P. P.; Kowalczyk, B.; Pudlo, W. J.; Grzybowski, B. A. Electrostatic Titrations Reveal Surface Compositions of Mixed, On-Nanoparticle Monolayers Comprising Positively and Negatively Charged Ligands. J. Phys. Chem. C 2016, 120 (7), 4139– 4144,  DOI: 10.1021/acs.jpcc.5b12599
      30
      Electrostatic Titrations Reveal Surface Compositions of Mixed, On-Nanoparticle Monolayers Comprising Positively and Negatively Charged Ligands
      Pillai, Pramod P.; Kowalczyk, Bartlomiej; Pudlo, Wojciech J.; Grzybowski, Bartosz A.
      Journal of Physical Chemistry C (2016), 120 (7), 4139-4144CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      A general-purpose procedure based on electrostatic titrns. was developed to det. the compns. of mixed self-assembled monolayers (m-SAMs) of oppositely charged ligands on metal nanoparticles (NPs). In this procedure, nanoparticles of unknown m-SAM compns. and charges are titrated with the pos. charged NP "stds.". These compns. and the differences in the free energies of adsorption of the [+] and [-] are then detd. from the points of pptn. at which the overall charge on all NPs is neutralized. The results of the titrns. agree well with traditional core-etching/NMR studies. However, the titrn.-based approach is nondestructive and requires significantly less material than NMR.
    31. 31
      Peter, B.; Lagzi, I.; Teraji, S.; Nakanishi, H.; Cervenak, L.; Zámbó, D.; Deák, A.; Molnár, K.; Truszka, M.; Szekacs, I.; Horvath, R. Interaction of Positively Charged Gold Nanoparticles with Cancer Cells Monitored by an in Situ Label-Free Optical Biosensor and Transmission Electron Microscopy. ACS Appl. Mater. Interfaces 2018, 10 (32), 26841– 26850,  DOI: 10.1021/acsami.8b01546
      31
      Interaction of Positively Charged Gold Nanoparticles with Cancer Cells Monitored by an in Situ Label-Free Optical Biosensor and Transmission Electron Microscopy
      Peter, Beatrix; Lagzi, Istvan; Teraji, Satoshi; Nakanishi, Hideyuki; Cervenak, Laszlo; Zambo, Daniel; Deak, Andras; Molnar, Kinga; Truszka, Monika; Szekacs, Inna; Horvath, Robert
      ACS Applied Materials & Interfaces (2018), 10 (32), 26841-26850CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      Functionalized nanoparticles (NPs) can penetrate into living cells and vesicles, opening up an extensive range of novel directions. For example, NPs are intensively employed in targeted drug delivery and biomedical imaging. However, the real-time kinetics and dynamics of NP-living cell interactions remained uncovered. In this study, the authors in situ monitored the cellular uptake of gold NPs-functionalized with pos. charged alk. thiol-into surface-adhered cancer cells, by using a high-throughput label-free optical biosensor employing resonant waveguide gratings. The characteristic kinetic curves upon NP exposure of cell-coated biosensor surfaces were recorded and compared to the kinetics of NP adsorption onto bare sensor surfaces. The authors demonstrated that from the above kinetic information, one can conclude about the interactions between the living cells and the NPs. Real-time biosensor data suggested the cellular uptake of the functionalized NPs by an active process. It was found that pos. charged particles penetrate into the cells more effectively than neg. charged control particles, and the optimal size for the cellular uptake of the pos. charged particles is around 5 nm. These conclusions were obtained in a cost-effective, fast, and high-throughput manner. The fate of the NPs was further revealed by electron microscopy on NP-exposed and subsequently fixed cells, well confirming the results obtained by the biosensor. Moreover, an ultrastructural study demonstrated the involvement of the endosomal-lysosomal system in the uptake of functionalized NPs and suggested the type of the internalization pathway.
    32. 32
      Nakanishi, H.; Deák, A.; Hólló, G.; Lagzi, I. Existence of a Precipitation Threshold in the Electrostatic Precipitation of Oppositely Charged Nanoparticles. Angew. Chem., Int. Ed. 2018, 57 (49), 16062– 16066,  DOI: 10.1002/anie.201809779
      32
      Existence of a Precipitation Threshold in the Electrostatic Precipitation of Oppositely Charged Nanoparticles
      Nakanishi, Hideyuki; Deak, Andras; Hollo, Gabor; Lagzi, Istvan
      Angewandte Chemie, International Edition (2018), 57 (49), 16062-16066CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Oppositely charged nanoparticles ppt. rapidly only at the point of electroneutrality, wherein their charges are macroscopically compensated. We investigated the aggregation and pptn. of oppositely charged nanoparticles at concns. ranging from 10 to 10-3 mM (based on gold atoms) by using UV/Vis measurements. We employed solns. of equally sized (4.6 nm) gold nanoparticles, which were functionalized and stabilized with either pos. or with neg. charged alkanethiols. Results showed that oppositely charged nanoparticles do not ppt. if their concn. is below a certain threshold even if the electroneutrality condition is fulfilled. This finding suggests a universal behavior of chem. systems comprising oppositely charged building blocks such as ions and charged nanoparticles.
    33. 33
      Kalsin, A. M.; Fialkowski, M.; Paszewski, M.; Smoukov, S. K.; Bishop, K. J. M.; Grzybowski, B. A. Electrostatic Self-Assembly of Binary Nanoparticle Crystals with a Diamond-Like Lattice. Science 2006, 312 (5772), 420– 424,  DOI: 10.1126/science.1125124
      33
      Electrostatic Self-Assembly of Binary Nanoparticle Crystals with a Diamond-Like Lattice
      Kalsin, Alexander M.; Fialkowski, Marcin; Paszewski, Maciej; Smoukov, Stoyan K.; Bishop, Kyle J. M.; Grzybowski, Bartosz A.
      Science (Washington, DC, United States) (2006), 312 (5772), 420-424CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      A review. Self-assembly of charged, equally sized metal nanoparticles of 2 types (Au and Ag) gives large, sphalerite (diamond-like) crystals, in which each nanoparticle has 4 oppositely charged neighbors. Formation of these nonclose-packed structures is a consequence of electrostatic effects specific to the nanoscale, where the thickness of the screening layer is commensurate with the dimensions of the assembling objects. Because of electrostatic stabilization of larger crystg. particles by smaller ones, better-quality crystals can be obtained from more polydisperse nanoparticle solns.
    34. 34
      Calvert, J. G. Glossary of Atmospheric Chemistry Terms (Recommendations 1990). Pure Appl. Chem. 1990, 62 (11), 2167– 2219,  DOI: 10.1351/pac199062112167
      34
      Glossary of atmospheric chemistry terms. (Recommendations 1990)
      Calvert, Jack G.
      Pure and Applied Chemistry (1990), 62 (11), 2167-219CODEN: PACHAS; ISSN:0033-4545.
      A glossary of terms used in atm. chem. and related fields is compiled, including to those related to clouds, solar radiation, air quality control, etc.
    35. 35
      Yu, W. L.; Matijević, E.; Borkovec, M. Absolute Heteroaggregation Rate Constants by Multiangle Static and Dynamic Light Scattering. Langmuir 2002, 18 (21), 7853– 7860,  DOI: 10.1021/la0203382
      35
      Absolute Heteroaggregation Rate Constants by Multiangle Static and Dynamic Light Scattering
      Yu, W. L.; Matijevic, E.; Borkovec, M.
      Langmuir (2002), 18 (21), 7853-7860CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)
      The anal. of early-stage heteroaggregation (or heterocoagulation) in binary colloidal systems composed of oppositely charged latex particles of different size in the submicrometer size range with multiangle static and dynamic light scattering is presented. The soln. conditions were adjusted to exclude any significant homoaggregation. The apparent rate obtained from static light scattering mostly strongly decreases with increasing scattering angle regardless of the no. fractions, while the rate from dynamic light scattering varies in a more complicated manner. The light scattering data could be interpreted quant. from the Rayleigh-Gans-Debye approxn. The values of abs. heteroaggregation rate consts. are the same within exptl. error when evaluated from static or dynamic light scattering, and they were independent of the mixing ratio. The av. hydrodynamic radius of the doublet obtained from the dynamic light scattering was in good agreement with theor. ests. based on an exact hydrodynamic treatment at low Reynolds nos. A simple formula is proposed to est. the hydrodynamic radius of the asym. particle doublet, and this formula is shown to agree well with exptl. data and with theory. The new conclusion from this study is that multiangle dynamic light scattering represents the method of choice for the detn. of abs. heteroaggregation rate consts.
    36. 36
      Haiss, W.; Thanh, N. T. K.; Aveyard, J.; Fernig, D. G. Determination of Size and Concentration of Gold Nanoparticles from UV-Vis Spectra. Anal. Chem. 2007, 79 (11), 4215– 4221,  DOI: 10.1021/ac0702084
      36
      Determination of Size and Concentration of Gold Nanoparticles from UV-Vis Spectra
      Haiss, Wolfgang; Thanh, Nguyen T. K.; Aveyard, Jenny; Fernig, David G.
      Analytical Chemistry (Washington, DC, United States) (2007), 79 (11), 4215-4221CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      The dependence of the optical properties of spherical gold nanoparticles on particle size and wavelength were analyzed theor. using multipole scattering theory, where the complex refractive index of gold was cor. for the effect of a reduced mean free path of the conduction electrons in small particles. To compare these theor. results to exptl. data, gold nanoparticles in the size range of 5 to 100 nm were synthesized and characterized with TEM and UV-visible. Excellent agreement was found between theory and expt. The data produced here can be used to det. both size and concn. of gold nanoparticles directly from UV-visible spectra. Equations for this purpose are derived, and the precision of various methods is discussed. The major aim of this work is to provide a simple and fast method to det. size and concn. of nanoparticles.
    37. 37
      Hendel, T.; Wuithschick, M.; Kettemann, F.; Birnbaum, A.; Rademann, K.; Polte, J. In Situ Determination of Colloidal Gold Concentrations with UV-Vis Spectroscopy: Limitations and Perspectives. Anal. Chem. 2014, 86 (22), 11115– 11124,  DOI: 10.1021/ac502053s
      37
      In Situ Determination of Colloidal Gold Concentrations with UV-Vis Spectroscopy: Limitations and Perspectives
      Hendel, Thomas; Wuithschick, Maria; Kettemann, Frieder; Birnbaum, Alexander; Rademann, Klaus; Polte, Joerg
      Analytical Chemistry (Washington, DC, United States) (2014), 86 (22), 11115-11124CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      This paper studies the UV-visible absorbance of colloidal gold nanoparticles at 400 nm and validates it as a method to det. Au(0) concns. in colloidal gold solns. The method is valid with restrictions depending on the studied system. The uncertainty of the detd. Au(0) concn. can be up to 30%. This deviation is the result of the combined influence of parameters such as particle size, surface modification, or oxidn. state. However, quantifying the influence of these parameters enables a much more precise Au(0) detn. for specific systems. As an example, the redn. process of the known Turkevich method was monitored and the Au(0) concn. was detd. with a deviation of <5%. Hence, a simple, fast, easy, and cheap in situ method for Au(0) detn. is demonstrated that has in the presence of other gold species such as Au(III) an unprecedented accuracy.
    38. 38
      Liu, X.; Atwater, M.; Wang, J.; Huo, Q. Extinction Coefficient of Gold Nanoparticles with Different Sizes and Different Capping Ligands. Supramol. Chem. Appl. Interfaces 2007, 58 (1), 3– 7,  DOI: 10.1016/j.colsurfb.2006.08.005
      There is no corresponding record for this reference.
    39. 39
      Punj, D.; Regmi, R.; Devilez, A.; Plauchu, R.; Moparthi, S. B.; Stout, B.; Bonod, N.; Rigneault, H.; Wenger, J. Self-Assembled Nanoparticle Dimer Antennas for Plasmonic-Enhanced Single-Molecule Fluorescence Detection at Micromolar Concentrations. ACS Photonics 2015, 2 (8), 1099– 1107,  DOI: 10.1021/acsphotonics.5b00152
      39
      Self-Assembled Nanoparticle Dimer Antennas for Plasmonic-Enhanced Single-Molecule Fluorescence Detection at Micromolar Concentrations
      Punj, Deep; Regmi, Raju; Devilez, Alexis; Plauchu, Robin; Moparthi, Satish Babu; Stout, Brian; Bonod, Nicolas; Rigneault, Herve; Wenger, Jerome
      ACS Photonics (2015), 2 (8), 1099-1107CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
      Plasmonic antennas offer extremely promising strategies to enhance single mol. fluorescence sensing and breach the limitations set by diffraction. However, the tech. difficulty and limited availability of top-down nanofabrication techniques enabling nanometer gap sizes are limiting the impact of plasmonic antennas for biochem. and biophys. applications. Here we demonstrate the effectiveness of self-assembled nanoparticle gap antennas to enhance single mol. fluorescence detection at high concns. For a dimer of 80 nm gold nanoparticles with 6 nm gap, we isolate detection vols. down to 70 zL (equiv. to λ3/3600) and achieve 600-fold fluorescence enhancement, microsecond transit time, and operation of fluorescence correlation spectroscopy at concns. exceeding 10 μM. We quantify the near-field detection vol. and the fluorescence enhancement for different self-assembled nanoantenna designs using fluorescence correlation spectroscopy. The combination of the fabrication simplicity with the large fluorescence enhancement makes the self-assembled colloidal nanoparticle gap antennas optimal to extend a wide variety of single-mol. applications toward the biol. relevant micromolar concn. regime.
    40. 40
      Biggs, S.; Mulvaney, P. Measurement of the Forces between Gold Surfaces in Water by Atomic Force Microscopy. J. Chem. Phys. 1994, 100 (11), 8501– 8505,  DOI: 10.1063/1.466748
      40
      Measurement of the forces between gold surfaces in water by atomic force microscopy
      Biggs, Simon; Mulvaney, Paul
      Journal of Chemical Physics (1994), 100 (11), 8501-5CODEN: JCPSA6; ISSN:0021-9606.
      The forces between a flat Au surface and a Au-coated silica sphere were measured in H2O by using an at. force microscope. A long-range attractive interaction is obsd. which is ascribed to the van der Waals interaction between the 2 surfaces. The force data agree extremely well with recent, calcd. values of the Hamaker function (including retardation) for Au/H2O/Au. The best fit to the exptl. data yields a value of 2.5 ± 0.5 × 10-19 J for the unretarded Hamaker const. In the presence of CTAB monolayers, electrostatic repulsion is obsd. at all distances for Au sphere (radius 3.3 μm) interactions with a flat Au surface. However, an attractive force is obsd. at very small sepns. for Au-coated Si3N4 tips (effective radius 0.1 μm), which is attributed to penetration of the CTAB monolayers by the sharper tip.

  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpclett.3c01857.

    • Synthesis of gold nanoparticles and description of the measurements, description of the extended mathematical model, and Figures S1–S10 showing the calculated overall potentials, the precipitation of oppositely charged gold nanoparticles with the concentration of 0.26 mM; results of the extended mathematical model, and the effect of the dispersity of the sample on the precipitation window (PDF)

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