Vladimir E. Bochenkov

Spatial Mapping and Quantification of Soft and Hard Protein Coronas at Silver Nanocubes

Protein coronas around silver nanocubes were quantified in serum-containing media using localized surface plasmon resonances. Both soft and hard coronas showed exposure-time and concentration-dependent changes in protein surface density with time-dependent hardening. We observed spatially dependent kinetics of the corona-formation at cube edges/corners versus facets at short incubation times, where the polymer stabilization agent delayed corona hardening. The soft corona contained more protein than the hard corona at all time-points (8-fold difference with 10% serum conditions).

From rings to crescents: a novel fabrication technique uncovers the transition details

A novel fabrication route is reported for the generation of substrate-supported symmetric and asymmetric metal nanostructures. We combine a colloidal template and angled evaporation to deposit in situ mask materials for subsequent lithographic pattern transfer. The technique is demonstrated for the fabrication of concentric and nonconcentric gold rings and crescents. Optical properties of localized plasmon resonances in such structures are studied by UV-vis-NIR spectroscopy and finite-difference time domain simulations during the transition from rings to crescents revealing the development of strong quadrupolar modes.

Sensor activity of thin polymer films containing lead nanoparticles

Thin poly(p-xylylene) films containing lead nanoparticles were prepared by vacuum deposition technique. The vapors of p-xylylene monomer and lead were condensed onto the surfaces cooled down to 80 K. Films thus obtained were characterized by electric conductivity measurements during film samples formation. Such metallopolymer films exhibit sensor activity in the presence of ammonia in the atmospheric air. The influence of air humidity and the co-operative effect of ammonia together with water vapors on film resistance were studied.

Dynamic protein coronas revealed as a modulator of silver nanoparticle sulphidation in vitro

Proteins adsorbing at nanoparticles have been proposed as critical toxicity mediators and are included in ongoing efforts to develop predictive tools for safety assessment. Strongly attached proteins can be isolated, identified and correlated to changes in nanoparticle state, cellular association or toxicity. Weakly attached, rapidly exchanging proteins are also present at nanoparticles, but are difficult to isolate and have hardly been examined. Here we study rapidly exchanging proteins and show for the first time that they have a strong modulatory effect on the biotransformation of silver nanoparticles. Released silver ions, known for their role in particle toxicity, are found to be trapped as silver sulphide nanocrystals within the protein corona at silver nanoparticles in serum-containing cell culture media. The strongly attached corona acts as a site for sulphidation, while the weakly attached proteins reduce nanocrystal formation in a serum-concentration-dependent manner. Sulphidation results in decreased toxicity of Ag NPs.

Enhanced refractive index sensitivity of elevated short-range ordered nanohole arrays in optically thin plasmonic Au films.

A simple development of the colloidal lithography technique is demonstrated for fabrication of perforated plasmonic metal films elevated above the substrate surface. The bulk refractive index sensitivity of short-range ordered nanohole arrays in 20 nm thick Au films exhibits an increase of up to 37% due to reduction of substrate effect caused by lifting with a 40 nm silica layer. Analysis of the local electric field distribution suggests that the sensitivity increase is due to revealing of the enhanced field near the holes.

HArF in Solid Argon Revisited: Transition from Unstable to Stable Configuration

The thermal conversion of HArF configurations in solid argon has been investigated both experimentally and theoretically. The matrix isolation experiments have been concentrated on temperatures 25-27 K, promoting the transition from the unstable to stable HArF configuration. The combined quantum mechanical-molecular mechanical and temperature-accelerated dynamics approach has been developed to study the real-time evolution of HArF trapped in different matrix-site morphologies. Two realistic pathways of the stable HArF formation are found for annealing at 25-27 K. The conversion mechanism in both pathways involves the local mobility of matrix vacancies in the vicinity of the HArF molecule. These two relaxation processes occurring within different timescales can cause the multiexponential decay of unstable HArF observed experimentally. The theoretical values of the activation energy of 64 meV as well as the corresponding pre-exponential factor of exp(28) s(-1), obtained for one of the unstable HArF configurations, are well consistent with the experimental estimates of 70 meV and exp(30 +/- 3) s(-1), respectively.

Onset of bonding plasmon hybridization preceded by gap modes in dielectric splitting of metal disks.

Dielectric splitting of nanoscale disks was studied experimentally and via finite-difference time-domain (FDTD) simulations through systematic introduction of multiple ultrathin dielectric layers. Tunable, hybridized dark bonding modes were seen with first-order gap modes preceding the appearance of bonding dipole-dipole disk modes. The observed bright dipolar mode did not show the energy shift expected from plasmon hybridization but activated dark higher order gap modes. Introducing lateral asymmetry was shown to remodel the field distribution resulting in 3D asymmetry that reoriented the dipole orientation away from the dipole of the elementary disk modes.

Complex protein nanopatterns over large areas via colloidal lithography.

The patterning of biomolecules at the nanoscale provides a powerful method to investigate cellular adhesion processes. A novel method for patterning is presented that is based on colloidal monolayer templating combined with multiple and angled deposition steps. Patterns of gold and SiO2 layers are used to generate complex protein nanopatterns over large areas. Simple circular patches or more complex ring structures are produced in addition to hierarchical patterns of smaller patches. The gold regions are modified through alkanethiol chemistry, which enables the preparation of extracellular matrix proteins (vitronectin) or cellular ligands (the extracellular domain of E-cadherin) in the nanopatterns, whereas the selective poly(l-lysine)-poly(ethylene glycol) functionalization of the SiO2 matrix renders it protein repellent. Cell studies, as a proof of principle, demonstrate the potential for using sets of systematically varied samples with simpler or more complex patterns for studies of cellular adhesive behavior and reveal that the local distribution of proteins within a simple patch critically influences cell adhesion.

Extended temperature-accelerated dynamics: Enabling long-time full-scale modeling of large rare-event systems

A new method, the Extended Temperature-Accelerated Dynamics (XTAD), is introduced for modeling long-timescale evolution of large rare-event systems. The method is based on the Temperature-Accelerated Dynamics approach [M. Sørensen and A. Voter, J. Chem. Phys. 112, 9599 (2000)], but uses full-scale parallel molecular dynamics simulations to probe a potential energy surface of an entire system, combined with the adaptive on-the-fly system decomposition for analyzing the energetics of rare events. The method removes limitations on a feasible system size and enables to handle simultaneous diffusion events, including both large-scale concerted and local transitions. Due to the intrinsically parallel algorithm, XTAD not only allows studies of various diffusion mechanisms in solid state physics, but also opens the avenue for atomistic simulations of a range of technologically relevant processes in material science, such as thin film growth on nano- and microstructured surfaces.

Adsorption, catalysis, and reactions on the surfaces of metal nano-oxides

Nanomaterials based on metal oxides are considered. Special attention is given to adsorption, because this step determines physicochemical properties of nanostructured materials. The main processes are considered that occur on the surface of metal nano-oxides in the course of adsorption and the nature of chemoresistance. A model is presented that explains the increasing sensitivity of semiconductor sensor materials with a decrease in the grain size. The potential of the use of metal and metal oxide nanoparticles in catalysis and photocatalysis is discussed. Examples are given for the selective synthesis of α-mercaptopyridine on the surface of TiO2 with supported silver nanoparticles with a diameter of <1 nm. Possible problems that might appear when nanoparticles are used in large-scale manufactures are discussed. Promising examples of the use of magnesium and calcium oxide nanoparticles for the destruction of toxic substances, specifically 3,3-dimethyl-2-butylmethylphosphoxofluoride and dichloroethyl sulfide at room temperature are analyzed. The method of cryoformation is considered that makes it possible to create new nanomaterials for use in catalysis, in gas sensors, and for modifying pharmaceuticals to reach a higher biological activity.