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Multivalent ligand-receptor interactions between receptor-presenting lipid membranes and ligand-modified biological and biomimetic nanoparticles influence cellular entry and fusion processes. Environmental pH changes can drive these membrane-related interactions by affecting membrane nanomechanical properties. Quantitatively, however, the corresponding effects on high-curvature, sub-100 nm lipid vesicles are scarcely understood, especially in the multivalent binding context. Herein, we employed the label-free localized surface plasmon resonance (LSPR) sensing technique to track the multivalent attachment kinetics, shape deformation, and surface coverage of biotin ligand-functionalized, zwitterionic lipid vesicles with different ligand densities on a streptavidin receptor-coated supported lipid bilayer under varying pH conditions (4.5, 6, 7.5). Our results demonstrate that more extensive multivalent interactions caused greater vesicle shape deformation across the tested pH conditions, which affected vesicle surface packing as well. Notably, there were also pH-specific differences, i.e., a higher degree of vesicle shape deformation was triggered at a lower multivalent binding energy in pH 4.5 than in pH 6 and 7.5 conditions. These findings support that the nanomechanical properties of high-curvature lipid membranes, especially the membrane bending energy and the corresponding responsiveness to multivalent binding interactions, are sensitive to solution pH, and indicate that multivalency-induced vesicle shape deformation occurs slightly more readily in acidic pH conditions relevant to biological environments.

In applications of bio-inspired nanoparticles (NPs), their composition is often optimised by including ionizable lipids. I use a generic statistical model to describe the charge and potential distributions in lipid nanoparticles (LNPs) containing such lipids. The LNP structure is considered to contain the biophase regions separated by narrow interphase boundaries with water. Ionizable lipids are uniformly distributed at the biophase-water boundaries. The potential is there described at the mean-filed level combining the Langmuir-Stern equation for ionizable lipids and the Poisson-Boltzmann equation for other charges in water. The latter equation is used outside a LNP as well. With physiologically reasonable parameters, the model predicts the scale of the potential in a LNP to be rather low, smaller or about [Formula: see text], and to change primarily near the LNP-solution interface or, more precisely, inside an NP near this interface because the charge of ionizable lipids becomes rapidly neutralized along the coordinate towards the center of a LNP. The extent of dissociation-mediated neutralization of ionizable lipids along this coordinate increases but only slightly. Thus, the neutralization is primarily due to the negative and positive ions related to the ionic strength in solution and located inside a LNP., (© 2023. The Author(s).)

Lipid nanoparticles (LNPs) have emerged as potent carriers for mRNA delivery, but several challenges remain before this approach can offer broad clinical translation of mRNA therapeutics. To improve their efficacy, a better understanding is required regarding how LNPs are trapped and processed at the anionic endosomal membrane prior to mRNA release. We used surface-sensitive fluorescence microscopy with single LNP resolution to investigate the pH dependency of the binding kinetics of ionizable lipid-containing LNPs to a supported endosomal model membrane. A sharp increase of LNP binding was observed when the pH was lowered from 6 to 5, accompanied by stepwise large-scale LNP disintegration. For LNPs preincubated in serum, protein corona formation shifted the onset of LNP binding and subsequent disintegration to lower pH, an effect that was less pronounced for lipoprotein-depleted serum. The LNP binding to the endosomal membrane mimic was observed to eventually become severely limited by suppression of the driving force for the formation of multivalent bonds during LNP attachment or, more specifically, by charge neutralization of anionic lipids in the model membrane due to their association with cationic lipids from earlier attached LNPs upon their disintegration. Cell uptake experiments demonstrated marginal differences in LNP uptake in untreated and lipoprotein-depleted serum, whereas lipoprotein-depleted serum increased mRNA-controlled protein (eGFP) production substantially. This complies with model membrane data and suggests that protein corona formation on the surface of the LNPs influences the nature of the interaction between LNPs and endosomal membranes.

Time-resolved measurements of changes in the size and shape of nanobiological objects and layers are crucial to understand their properties and optimize their performance. Optical sensing is particularly attractive with high throughput and sensitivity, and label-free operation. However, most state-of-the-art solutions require intricate modeling or multiparameter measurements to disentangle conformational or thickness changes of biomolecular layers from complex interfacial refractive index variations. Here, we present a dual-band nanoplasmonic ruler comprising mixed arrays of plasmonic nanoparticles with spectrally separated resonance peaks. As electrodynamic simulations and model experiments show, the ruler enables real-time simultaneous measurements of thickness and refractive index variations in uniform and heterogeneous layers with sub-nanometer resolution. Additionally, nanostructure shape changes can be tracked, as demonstrated by quantifying the degree of lipid vesicle deformation at the critical coverage prior to rupture and supported lipid bilayer formation. In a broader context, the presented nanofabrication approach constitutes a generic route for multimodal nanoplasmonic optical sensing.

The mechanical properties of biological nanoparticles play a crucial role in their interaction with the cellular membrane, in particular for cellular uptake. This has significant implications for the design of pharmaceutical carrier particles. In this context, liposomes have become increasingly popular, among other reasons due to their customizability and easily varied physicochemical properties. With currently available methods, it is, however, not trivial to characterize the mechanical properties of nanoscopic liposomes especially with respect to the level of deformation induced upon their ligand-receptor-mediated interaction with laterally fluid cellular membranes. Here, we utilize the sensitivity of dual-wavelength surface plasmon resonance to probe the size and shape of bound liposomes (∼100 nm in diameter) as a means to quantify receptor-induced deformation during their interaction with a supported cell membrane mimic. By comparing biotinylated liposomes in gel and fluid phases, we demonstrate that fluid-phase liposomes are more prone to deformation than their gel-phase counterparts upon binding to the cell membrane mimic and that, as expected, the degree of deformation depends on the number of ligand-receptor pairs that are engaged in the multivalent binding.

The size of membrane-enveloped virus particles, exosomes, and lipid vesicles strongly impacts functional properties in biological and applied contexts. Multivalent ligand-receptor interactions involving nanoparticle shape deformation are critical to such functions, yet the corresponding effect of nanoparticle size remains largely elusive. Herein, using an indirect nanoplasmonic sensing approach, we investigated how the nanoscale size properties of ligand-modified lipid vesicles affect real-time binding interactions, especially vesicle deformation processes, with a receptor-modified, cell membrane-mimicking platform. Together with theoretical analyses, our findings reveal a pronounced, size-dependent transition in the membrane bending properties of nanoscale lipid vesicles between 60 and 180 nm in diameter. For smaller vesicles, a large membrane bending energy enhanced vesicle stiffness while the osmotic pressure energy was the dominant modulating factor for larger, less stiff vesicles. These findings advance our fundamental understanding of how nanoparticle size affects multivalency-induced nanoparticle shape deformation and can provide guidance for the design of biomimetic nanoparticles with tailored nanomechanical properties.

In biofluids containing various proteins, nanoparticles rapidly come to be surrounded by a nanometer-thick protein layer referred to as a protein corona. The late stage of this process occurs via replacement of proteins already bound to a nanoparticle by new ones. In the available kinetic models, this process is considered to include independent acts of protein detachment and attachment. It can, however, occur also at the level of protein pairs via exchange, i.e., concerted replacement of an attached protein by a newly arrived one. I argue that the exchange channel can be more important than the conventional one. To illustrate the likely specifics of the exchange channel, I present a kinetic model focused exclusively on this channel and based on the Evans-Polanyi-type relation between the activation energies of the protein-exchange steps and the protein binding energies. The corresponding kinetics were calculated for three qualitatively different distributions of proteins in solution over binding energy (with a maximum or monotonously decreasing or increasing, respectively) and are found to be similar, with relatively rapid replacement of weakly bound proteins and slow redistribution of strongly bound proteins. The ratio of the timescales characterizing the evolution of weakly and strongly bound proteins is found to depend on the type of the binding-energy distribution.

By analogy with virions, the binding of biologically-inspired nanoparticles (NPs) with ligands to the cellular membrane containing receptors depends on the multivalent ligand-receptor interaction, membrane bending, and cytoskeleton deformation. The interplay of these factors results in the existence of the potential minimum and activation barrier on the pathway towards full absorption of a NP. Herein, I hypothesize and show theoretically that the interaction of a NP, bound to one cell, with another cell can stabilize the potential minimum and increase the corresponding activation barrier, i.e., NPs can mediate the formation of long-living pairs of cells and aggregates containing a few cells inside blood and lymphatic vessels., (Copyright © 2021 The Author. Published by Elsevier B.V. All rights reserved.)

In-depth understanding of the intricate interactions between biomolecules and nanoparticles is hampered by a lack of analytical methods providing quantitative information about binding kinetics. Herein, we demonstrate how label-free evanescent light-scattering microscopy can be used to temporally resolve specific protein binding to individual surface-bound (∼100 nm) lipid vesicles. A theoretical model is proposed that translates protein-induced changes in light-scattering intensity into bound mass. Since the analysis is centered on individual lipid vesicles, the signal from nonspecific protein binding to the surrounding surface is completely avoided, offering a key advantage over conventional surface-based techniques. Further, by averaging the intensities from less than 2000 lipid vesicles, the sensitivity is shown to increase by orders of magnitude. Taken together, these features provide a new avenue in studies of protein-nanoparticle interaction, in general, and specifically in the context of nanoparticles in medical diagnostics and drug delivery.

Dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) are widely used to determine the size of biological nanoparticles in liquid. In both cases, one first measures the nanoparticle diffusion coefficient and then converts it to the nanoparticle radius via the Stokes-Einstein relation. This relation is based on the no-slip boundary condition. Now, there is evidence that this condition can be violated in biologically relevant cases (e.g., for vesicles) and that in such situations the partial-slip boundary condition is more suitable. I show (i) how the latter condition can be employed in the context of DLS and NTA and (ii) that the use of the former condition may result in underestimation of the nanoparticle radius by about 10 nm compared with the nominal one.

Various RNAs (siRNAs, miRNAs, or mRNAs) can be delivered into cells by lipid nanoparticles (LNPs) of 50-150 nm in diameter. The subsequent RNA release from LNPs may occur via various scenarios. Herein, two related kinetic models are proposed. The first model takes into account that LNPs are often porous so that RNA molecules diffuse in and detach from nanopores. The analysis is focused on RNA diffusion from a pore. The analytical expression obtained for the RNA escape rate constant is used to identify the difference in the release of siRNAs, miRNAs, and mRNAs. The key message here is that the mRNA diffusion from pores appears to be too slow, and accordingly the mRNA release seems to occur primarily via degradation of LNPs. The second coarse-grained model describes the diffusion-mediated release of RNA from a LNP in the situation when this process is accompanied by the LNP degradation at the lipid-solution interface. The corresponding kinetics are shown in detail at different relative rates of the RNA diffusion and LNP degradation. Potentially, this can help to interpret drug plasma levels after various dosing regimens., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The van der Waals (vdW) interaction between nanoparticles (NPs) in general, and especially between metal NPs, may be appreciable, and may result in nanoparticle aggregation. In biofluids, NPs become rapidly surrounded by a protein corona (PC). Here, the vdW and hydration interaction of NPs with and without PC are compared in detail. The focus is on two widely used types of NPs fabricated of SiO 2 and Au and possessing weak and strong vdW interactions, respectively. For SiO 2 , the presence of PC increases the vdW interaction, but it remains relatively weak and insufficient for aggregation. For Au, the presence of PC decreases the vdW interaction, and in the case of small NPs (≤ 40 nm in diameter) it may become insufficient for aggregation as well while the larger NPs can aggregate.

Herein, I illustrate analytically how the global diffusion limitations can influence the first phase of the protein-corona formation at nanoparticles under conditions of intravascular injection. In particular, the concentrations of proteins near the boundaries of the injection region are shown to be comparable with those far from the region. In contrast, the concentrations of proteins inside the injection region may be dramatically smaller than those outside, and the ratio of these two concentrations for proteins of different size may be much higher, by a few orders of magnitude, for smaller proteins. These differences in the spatial distribution of proteins are expected to play a key role in the Vroman effect at the onset of the protein-corona formation.

mRNA delivery into cells forms the basis for one of the new and promising ways to treat various diseases. Among suitable carriers, lipid nanoparticles (LNPs) with a size of about 100 nm are now often employed. Despite high current interest in this area, the understanding of the basic details of LNP-mediated mRNA delivery and function is limited. To clarify the kinetics of mRNA release from LNPs, the author uses three generic models implying (i) exponential, (ii) diffusion-controlled, and (iii) detachment-controlled kinetic regimes, respectively. Despite the distinct differences in these kinetics, the associated transient kinetics of mRNA translation to the corresponding protein and its degradation are shown to be not too sensitive to the details of the mRNA delivery by LNPs (or other nanocarriers). In addition, the author illustrates how this protein may temporarily influence the expression of one gene or a few equivalent genes. The analysis includes positive or negative regulation of the gene transcription via the attachment of the protein without or with positive or negative feedback in the gene expression. Stable, bistable, and oscillatory schemes have been scrutinized in this context.

Interaction of metal or oxide nanoparticles (NPs) with biological soft matter is one of the central phenomena in basic and applied biology-oriented nanoscience. Often, this interaction includes adsorption of suspended proteins on the NP surface, resulting in the formation of the protein corona around NPs. Structurally, the corona contains a "hard" monolayer shell directly contacting a NP and a more distant weakly associated "soft" shell. Chemically, the corona is typically composed of a mixture of distinct proteins. The corresponding experimental and theoretical studies have already clarified many aspects of the corona formation. The process is, however, complex, and its understanding is still incomplete. Herein, we present a kinetic mean-field model of the formation of the "hard" corona with emphasis on the role of (i) protein-diffusion limitations and (ii) interplay between competitive adsorption of distinct proteins and irreversible reconfiguration of their native structure. The former factor is demonstrated to be significant only in the very beginning of the corona formation. The latter factor is predicted to be more important. It may determine the composition of the corona on the time scales comparable or longer than a few hours., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Macromolecular association commonly occurs via dynamic engagement of multiple weak bonds referred to as multivalent interactions. The distribution of the number of bonds, combined with their strong influence on the residence time, makes it very demanding to quantify this type of interaction. To address this challenge in the context of virology, we mimicked the virion association to a cell membrane by attaching lipid vesicles (100 nm diameter) to a supported lipid bilayer via multiple, identical cholesterol-based DNA linker molecules, each mimicking an individual virion-receptor link. Using total internal reflection microscopy to track single attached vesicles combined with a novel filtering approach, we show that histograms of the vesicle diffusion coefficient D exhibit a spectrum of distinct peaks, which are associated with vesicles differing in the number, n, of linking DNA tethers. These peaks are only observed if vesicles with transient changes in n are excluded from the analysis. D is found to be proportional to 1/n, in excellent agreement with the free draining model, allowing to quantify transient changes of n on the single vesicle level and to extract transition rates between individual linking states. Necessary imaging conditions to extend the analysis to multivalent interactions in general are also reported.

Physicochemical properties of nanoparticles may depend on their size and shape and are traditionally assessed in ensemble-level experiments, which accordingly may be plagued by averaging effects. These effects can be eliminated in single-nanoparticle experiments. Using plasmonic nanospectroscopy, we present a comprehensive study of hydride formation thermodynamics in individual Pd nanocrystals of different size and shape, and find corresponding enthalpies and entropies to be nearly size- and shape-independent. The hysteresis observed is significantly wider than in bulk, with details depending on the specifics of individual nanoparticles. Generally, the absorption branch of the hysteresis loop is size-dependent in the sub-30 nm regime, whereas desorption is size- and shape-independent. The former is consistent with a coherent phase transition during hydride formation, influenced kinetically by the specifics of nucleation, whereas the latter implies that hydride decomposition either occurs incoherently or via different kinetic pathways.

In the treatments of diffusion-limited association of suspended nanoparticles, their diffusion coefficients are usually considered to be constant and equal to those given by conventional hydrodynamics for diffusion of single nanoparticles. In reality, according to hydrodynamics, these coefficients depend, however, on the distance between nanoparticles. I show how this dependence can influence the association rate.

In biofluids, nanoparticles rapidly become surrounded by a protein corona. This phenomenon started to attract attention 10 years ago. Since then, this subfield of colloid and interface science was among the most rapidly expanding and progressing. Owing to its strong relation to biology and applications, this area is rich in various questions to explore. The reviews of the corresponding experiments are already numerous. Herein, I focus on the related theory including conventional mean-field kinetic models, dynamic density functional theory, Monte Carlo simulations, and molecular dynamics simulations. The key concept here is that the formation of a protein corona depends on the interplay of competition of different proteins for the location near the nanoparticle–solution interface (Vroman effect) and denaturation at this interface. Although this concept is not new, many details of this interplay are still open for debate. [ABSTRACT FROM AUTHOR]

Abstract Experimental studies of dislocations in nanoparticles are just beginning. The corresponding theoretical models are still lacking. In this context, the author analyzes relaxation of a dislocation in a nanoparticle. Mechanistically, this process is considered to occur primarily via dislocation drift induced by the stress-related image forces. Elementary dislocation displacements include the formation of a kink at one of the sides of the dislocation line, its diffusion along this line, and annihilation at the opposite side. For this mechanism, the dependence of the time of dislocation disappearance on the nanoparticle size has been identified. Highlights • Relaxation of a dislocation in a nanoparticle occurs at facets. • The drift towards facets is induced by the image forces. • This process is mediated by kink diffusion along a dislocation. • All these aspects are theoretically scrutinized. • The expression for the time scale of the relaxation is derived. [ABSTRACT FROM AUTHOR]

Contacts of biological or biologically-inspired spherically shaped nanoparticles (e.g., virions or lipid nanoparticles used for intracellular RNA delivery) with a lipid membrane of cells are often mediated by multiple relatively weak ligand-receptor bonds. Such contacts can be studied at a supported lipid bilayer. The rupture of bonds can be scrutinized by using force spectroscopy. Bearing a supported lipid bilayer in mind, the author shows analytically that the corresponding dependence of the force on the nanoparticle displacement and the effect of the force on the bond-rupture activation energy are qualitatively different compared to what is predicted by the conventional Bell approximation. [ABSTRACT FROM AUTHOR]

Kinetic processes occurring with participation of metal or oxide nanoparticles (NPs) in solution near or inside nanochannels fabricated in a membrane can be influenced by van der Waals interaction with a membrane. In addition, hydrodynamic slowdown of NP diffusion may be important under such conditions. In applications, NPs of this category can be covered by a thin protein layer referred to as protein corona, which may prevent direct contact of NPs with a membrane. In this context, an analytical expression is presented for van der Waals interaction of a spherical NP with a membrane when a NP is located near or inside a cylindrical nanochannel at the channel axis. The interaction is shown to be often appreciable (much higher than the thermal energy) and strongly dependent on the coordinate. Taking this factor and slowdown of diffusion into account, a general expression for the permeability of a channel is derived. [ABSTRACT FROM AUTHOR]

Oxidation of metals can be influenced by the presence of electric field, lattice strain, rearrangement of the oxide structure, and formation of cracks in an oxide. The understanding of the interplay of these factors is still incomplete. We focus on the scenario including the oxide-grain growth. The model used implies that the whole process is limited by diffusion of metal or oxygen atoms along the grain boundaries as it was originally proposed by Fehlner and Mott for macroscopic samples. For nanoparticles, the model predicts a transition from the power-law oxide growth at low conversion to slower growth at high conversion. [ABSTRACT FROM AUTHOR]

In biosystems, vesicles, virions, or metal particles of size ∼100 nm often diffuse in solution and interact with short (<10 nm) flexible receptors immobilized in a lipid membrane. The attachment kinetics of such nanoparticles can be limited by diffusion globally or locally. In the latter case, the calculation of the attachment rate is complicated by the dependence of the diffusion coefficient on the distance between a particle and membrane. The analysis, taking this factor into account, shows that the attachment rate constant is proportional to the receptor length and nearly independent of the particle radius. [ABSTRACT FROM AUTHOR]

Abstract: Nanostructured semiconductor–electrolyte interfaces are of high current interest due to novel physics and potential applications. The understanding of the corresponding potential profiles is, however, lacking. Our calculations illustrate the specifics of the potential profiles in a semiconductor near the charged nano-patterned interface separating a semiconductor and electrolyte. The lateral size of patterns is considered to be appreciably larger than the double-layer thickness. Despite this condition, the potential profiles are found to change in both directions on the length scale comparable to the size of patterns. The identified gradients in the potential profiles may be useful in applications including, e.g., electron–hole pair excitation and separation. [Copyright &y& Elsevier]

The density functional theory is used to study the effect of lattice strain on hydrogen diffusion in Pd. The activation energy for this process is found to increase dramatically with increasing compressive lattice strain. In particular, the activation energy is close to double for an isotropic compression of 5% both in the α and β phases. For tensile strain, the activation energy is instead decreased. This finding has important consequences for the interpretation of various kinetic processes occurring with participation of hydrogen and other interstitial atoms in macroscopic solid samples and nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract: We present a Schottky-type model describing dissolution and redeposition on Pt nanoparticles in polymer electrolyte fuel cells. The charge transfer is considered to occur near the surface of nanoparticles so that the potential barrier for the reaction is formed by the double-layer potential and the image interaction. With increasing electrode potential, the transfer coefficient for dissolution is found to decrease from 0.6–0.7 down to 0.3–0.4. Its dependence on the effective dielectric constant of the double layer is appreciable while the dependence on the particle size is weak. [Copyright &y& Elsevier]

Abstract: Metal nanoparticles can be used to enhance light absorption in photovoltaic nanocrystalline dye-sensitized solar cells. Our calculations scrutinizing this idea indicate, however, that the ratio of the rate of the induced power absorption by dyes, surrounding a nanoparticle, and the rate of the power dissipation by a nanoparticle is typically much lower than 0.5. Thus, this enhancement of light absorption seems to be practically inefficient. [ABSTRACT FROM AUTHOR]

Abstract: We analyse the kinetics of hydriding of metal nanoparticles in the generic case when the process is limited by diffusion of vacancies via the hydride shell. Our treatment is focused on the role of lattice strain related to the misfit of the hydride and metal structures. In the absence of strain, the kinetics exhibits an initial fast stage followed by slowdown. Depending on the relative contribution of strain to the H–metal interaction in the ground and activated states for diffusion, the initial fast stage of the kinetics is either nearly not manifested or becomes shorter and occurs up to somewhat higher conversion. [Copyright &y& Elsevier]

Abstract: In analogy with macroscopic metal samples, crystallization of metal nanoparticles may occur appreciably below the thermodynamic melting temperature, T m (this temperature depends on the particle size), while melting occurs at T m . If the surface melting is suppressed, nanoparticles can be overheated during melting. We describe these effects by using the classical nucleation theory and assuming that the nucleation starts at the particle corners or edges. The corresponding undercooling or overheating temperature intervals are found to be about 0.1T m for corners and 0.15T m for edges. These values are, respectively, two and one and a half times smaller than that for macroscopic samples. Under certain conditions, crystallization and melting can be controlled by the propagation of the front of a new phase. The corresponding temperature interval is found to be very narrow (about 0.02T m ). [Copyright &y& Elsevier]

Abstract: Using a novel indirect nanoplasmonic sensing platform, we have measured hydrogen absorption/desorption isotherms in Pd nanoparticles with an average diameter from 1.8 to 8nm at 30°C. The isotherms are fully reversible at relatively low and high pressures while at intermediate pressures there is hysteresis related to the hydride formation and decomposition. The hysteresis shrinks with decreasing particle size and becomes negligible for particles smaller than 2.5nm. This feature has been explained in terms of a diminishing contribution of lattice strain to the free energy of hydride formation as the particle size goes down. [Copyright &y& Elsevier]

Abstract: Hydriding and dehydriding kinetics of nanoparticles depend on the particle size. Our calculations illustrate that the apparent (averaged over size) kinetics of an ensemble of particles can be dramatically different compared to those of single particles. Specifically, we analyze the hydriding kinetics, limited by diffusion of hydrogen atoms from the surface layer via the hydride shell to the metallic core, and the dehydriding kinetics limited by associative desorption of hydrogen from the surface layer. In both cases, the apparent kinetics are relatively slow in the later stage, their time scale for the given average size is much larger than that for a single particle of the same size, and some of the special features of the single-particle kinetics (e.g., the initial slowdown of dehydriding) can be partly or completely washed out. The scaling of the time scale of the kinetics with respect to the particle size, however, remains valid. [Copyright &y& Elsevier]

Abstract: First-order phase transitions in nanoparticles (e.g., metal hydride formation) occur via absorption of species from or release to the gas or liquid phase. If the lattice strain is negligible, the uptake corresponding to a new phase exhibits a stepwise rise or drop with increasing or decreasing pressure or chemical potential of the absorbed species. With decreasing nanoparticle size, L, and increasing role of the surface and subsurface layers, this feature becomes less manifested because the system is less ideal. We present 3D lattice Monte Carlo simulations, explicitly illustrating this effect for L in the range from 100 down to 10 (L is measured in units of lattice spacing). [Copyright &y& Elsevier]

In the conventional Avrami–Kolmogorov–Johnson–Mehl model, the reaction or phase transition occurring in the 2D or 3D infinite medium is considered to start and proceed around randomly distributed and/or appearing nucleation centers. The radius of the regions transformed is assumed to linearly increase with time. The Monte Carlo simulations presented, illustrate what may happen if the transformation takes place in nanoparticles. The attention is focused on nucleation on the regular surface, edge and corner sites, and on the dependence of the activation energy for elementary reaction events on the local state of the sites. [ABSTRACT FROM AUTHOR]

Abstract: We present Monte Carlo simulations of the formation of a new phase (e.g., hydride in metal) during uptake of atoms by a nanoparticle. The corresponding kinetics exhibit a short initial stage, which is sensitive to the specification of the subsurface layers, and a more universal long stage with the time scale proportional to L z , where L is the lattice size, and 2.3⩽ z ⩽3 is the exponent dependent on the diffusion dynamics. For realistic diffusion dynamics, the model also predicts the third late stage when the growth of a new phase becomes very slow compared to that observed during the former stages. [Copyright &y& Elsevier]

Viral infections occur at very different length and time scales and include various processes, which can often be described using the models developed and/or employed in colloid and interface science. Bearing in mind the currently active COVID-19, I discuss herein the models aimed at viral transmission via respiratory droplets and the contact of virions with the epithelium. In a more general context, I outline the models focused on penetration of virions via the cellular membrane, initial stage of viral genome replication, and formation of viral capsids in cells. In addition, the models related to a new generation of drug delivery vehicles, for example, lipid nanoparticles with size about 100–200 nm, are discussed as well. Despite the high current interest in all these processes, their understanding is still limited, and this area is open for new theoretical studies. [Display omitted] [ABSTRACT FROM AUTHOR]

• The focus is on competitive receptor-mediated interaction of biological nanoparticles with a lipid membrane. • Attachment of nanoparticles of one type is considered to be followed by attachment of nanoparticles of the other type. • The latter nanoparticles can induce detachment of the former nanoparticles. • The corresponding kinetics are shown to be relatively gradual despite multiple bonds of each nanoparticle with receptors. • In addition, the kinetics may exhibit a distinct lag phase. The interaction of biological nanoparticles (e.g., ~ 100-nm-sized vesicles, micelles, and virions) with a lipid membrane is often multivalent and may include competition for receptors in situations when attachment of nanoparticles of one type occurs in parallel or is followed by attachment of nanoparticles of the other type. The nanoparticles adsorbed afterwards can induce detachment of the earlier adsorbed nanoparticles. I scrutinize theoretically this scenario in the case of a supported lipid bilayer. The corresponding kinetics are shown to be relatively gradual despite multiple bonds of each nanoparticle with receptors. In addition, the kinetics may exhibit a distinct lag phase. [ABSTRACT FROM AUTHOR]

Customarily, the Kirkendall effect is associated with the vacancy-mediated balance of diffusion fluxes of atoms at the interface between two metals. Nowadays, this effect attracts appreciable attention due to its crucial role in the formation of various hollow nanoparticles via oxidation of metal nanocrystallites. The understanding of the physics behind this effect in general and especially in the case of nanoparticles is still incomplete due to abundant complicating factors. Herein, the Kirkendall effect is illustrated in detail at the generic level by performing two-dimensional (2D) lattice Monte Carlo simulations of diffusion of A and B monomers with attractive nearest-neighbor interaction for times up to 107 Monte Carlo steps. Initially, A monomers are considered to form a close-packed array, while B monomers are in the 2D-gas state. The A-B interaction is assumed to be stronger compared to the other interactions, so that thermodynamically the c(2×2) A-B phase is preferable compared to the close-packed A phase (as in the case of metal oxidation). Depending on the relative rate of the diffusion jumps of A and B monomers, the patterns observed at the late stage of the formation of the mixed phase are shown to range from a single array without voids to those with appreciable disintegration of the initial array. In this way, the model predicts a single array with numerous small voids, a few moderate voids, or a single large void inside. [ABSTRACT FROM AUTHOR]

Abstract: Mattos and Aarao Reis [T.G. Mattos, F.D.A. Aarao Reis, J. Catal. 263 (2009) 67] have proposed a kinetic model of catalytic reaction including mass transport on a composite catalytic surface. We show that the boundary conditions for the reaction–diffusion equation they use contradict the prescription of the detailed balance principle for the relation between the rate constants for adsorbate diffusion jumps via the boundary and desorption from different areas, and, for certain parameters, the predictions of their model are qualitatively inconsistent. Quantitatively, their results are inconsistent in the situations where the role of the diffusion jumps from the catalytically active regions to the inactive regions is significant. [Copyright &y& Elsevier]