M. E. Kartseva

Metal Nanoparticles on Polymer Surfaces: 1. A New Method of Determining Glass Transition Temperature of the Surface Layer

New experimental approach allowing to study the structure and properties of polymer surface layers at a nanolevel is proposed. According to this method, metal nanoparticles are first adsorbed on a polymer surface from colloidal solution, then resultant system is stepwise annealed, and the particle embedding in a polymer is examined with atomic force microscope. Potentialities of the method are demonstrated using the gold nanoparticles–polystyrene system (including polystyrene modified with the UV radiation) as an example. It was established that the glass transition temperature of polystyrene surface layer is noticeably lower compared with the bulk value and decreases even more after the UV modification of a polymer surface. Possible use of the results obtained for the solution of other, independent problem, namely for the creation of “two-dimensional” nanocomposites by embedding nanoparticle monolayer ensemble in the surface layer of a glassy polymer at a temperature lower than the glass transition temperature of its bulk is analyzed.

Anisotropic particles with different morphologies of silver nanoshell: Synthesis and optical properties

Hydrosols of spindle-shaped composite particles with the core of iron(III) oxyhydroxide and silver shell are synthesized by enlarging metal seeding nanoparticles adsorbed on the surface of the cores in the solution containing silver nitrate and mild reducing agent. It is revealed that the character of the growth of shells on gold seeding particles greatly depends on the type of reducing agent. When using ascorbic acid, seeding particles grow primarily in the direction normal to the core surface due to the blocking of some of the particle faces by ions present in the solution. As a result, the forming shell is characterized by a fairly nonuniform structure. At the same time, when using formaldehyde, the growth of seeding nanoparticles proceeds predominantly in the lateral direction to form first an island-like film, then a continuous thin metal shell on the core surface. It is demonstrated that the position of localized surface plasmon resonance of such structure can be fine tuned to the preset wavelength by controlled variations in the thickness of Ag shell with very small step (up to 1 nm).

Metal nanoparticles on polymer surfaces: 6. Probing of non-glassy polystyrene surface layer

Peculiarities of the state of the surface layer of the amorphous glassy polymer polystyrene are studied with a specially developed experimental approach. The essence of the method consists in the observation via atomic force microscope for the depth and rate of embedding of gold nanoparticles in a polymer after their preliminary adsorption on the polymer surface from hydrosol. It is shown that the polymer glass-transition temperature near the boundary with air is substantially lowered relative to its bulk value. “Equilibrium” thickness of the non-glassy (“melted”) surface layer is determined through analysis of the data on the kinetics of nanoparticle embedding, and it is revealed that the layer thickness increases with temperature, reaching, near the “bulk” glass-transition temperature, the magnitude that is close to the diameter of the macromolecular coil. The results obtained are analyzed with allowance for published data, and the semi-empirical formula describing variations in the thickness of the non-glassy surface layer as a function of temperature in the interval between the “surface” and “bulk” glass-transition temperatures of a polymer is proposed.

Synthesis of anisotropic plasmonic nanoparticles with core-shell structure and prospects of their application in laser treatment of tumors

Aggregative stable dispersions of particles with anisotropic cores of iron(III) oxyhydroxide and gold or silver nanoshells are synthesized. They feature maximum plasmonic absorption at about 1000 nm (i.e., in the “optical window” of biological tissues). Such composite particles are of considerable interest for their potential use in cancer therapy. The possibility of finely tuning the position of localized surface plasmon resonance to the required wavelength is demonstrated for the FeOOH core/Au(Ag) shell nanostructures through a controlled variation of the metal shell thickness with a very small step (up to 1 nm). The surface modification of such composite particles by polyethylene glycol (PEG) considerably enhances the aggregative stability of their aqueous dispersions. Quantitative information about the distribution dynamics of the PEG-conjugated composite FeOOH core/Au shell particles in various organs and tissues of tumor-bearing mice has been obtained after an intravenous injection of a colloid solution of these particles. It is shown that composite particles can remain for a rather long time in a bloodstream without aggregation; moreover, their accumulation in a tumor takes place. Preliminary in vivo experiments have shown that PEGylated FeOOH core/Au(Ag) shell particles are effective thermosensibilizers in the pulse laser therapy of tumors.

A new method for loading mesoporous silica nanoparticles with drugs: Sol–gel synthesis using drug micelles as a template

It has been shown that mesoporous nanocontainers from SiO2 may be obtained by the sol–gel synthesis using drug (Miramistin) micelles as a template. The nanocontainers resulting from the combination of the stages of their synthesis and loading are characterized by a very high content of the drug (no less than 0.9 g per 1 g of SiO2). The kinetics of Miramistin desorption from the mesoporous particles into an aqueous medium has been studied under static and quasi-dynamic conditions. The desorption has been shown to rather strongly depend on pH. Possible mechanisms of the desorption process have been discussed.

Metal nanoparticles on polymer surfaces. 7. The growth kinetics of gold nanoparticles embedded into surface layers of glassy polymers

It has been shown that citrate gold nanoparticles can be embedded (partly immersed) into the surface layers of different glassy polymers with subsequent seeded growth of the particles in an aqueous chloroauric acid–hydroxylamine mixed solution. Quantitative data have been obtained on the seeded growth kinetics, and it has been shown that its rate-limiting stage is the diffusion of metal ions from the bulk solution to the surface of gold nanoparticles.

Metal Nanoparticles on Polymer Surfaces: 2. Catalytic Activity of Platinum Nanoparticle Ensembles on Polystyrene

Catalytic properties of platinum nanoparticles deposited onto polystyrene surface from their hydrosol stabilized with sodium polyacrylate are studied. It is shown that, during the adsorption on polymer substrate, metal nanoparticles form rather densely packed ordered monolayer ensembles with high catalytic activity in the model reaction of hydrogen reduction of methyl viologen. This allows one to measure the reaction rate with standard spectrometric method using polymer film with the surface area of 1 cm2 or less as a catalyst support.

Templateless Synthesis of Organosilica Nanotoroids and Creation of Core/Shell Plasmonic Structures Thereon

It has been shown for the first time that nanosized organosilica toroids can be formed via hydrolytic condensation of (γ-mercaptopropyl)trimethoxysilane in an alkaline medium. It has been found that such toroids may be used as “nuclei” for the synthesis of plasmonic composite nanoparticles with a core/shell structure.

Evolution of ultrafine gold seed nanoparticles with temperature and time and synthesis of plasmonic nanoshells

Features of the evolution of ultrafine gold nanoparticles synthesized by the Duff method with temperature and time have been studied in relation to their use as seeds for the formation of plasmonic nanoshells. A quantitative relation has been revealed between the duration of preheating of such particles at a preset temperature and their size. The obtained relation indicates that Au nanoparticles grow mainly via the Ostwald ripening mechanism. Using anisotropic composite FeOOH/Ag particles as an example, it has been shown that the obtained information may be used to substantially decrease the duration of the synthesis of metal nanoshells on diverse cores.

Possibilities of atomic spectroscopy in the analysis of gold- and silver-based nanoparticles in synthesized sols and biological samples

Possibilities of the determination of Au, Ag, and Si in dispersions of nanoparticles and biological samples by inductively coupled plasma atomic absorption and atomic emission spectrometry are demonstrated. Conditions of complete sample mineralization and the quantitative transfer of gold and silver to solution are found. The parameters of analyte determination in flame, graphite furnace, and plasma are optimized. The completeness of the atomization of gold, silver, and silicon in plasma on the introduction of nanoparticles as colloidal solutions is estimated. The conducted research allowed the estimation of the degree of gold and silver reduction at different stages of synthesis of composite nanoparticles with the core/shell structure. Quantitative information on the dynamics of accumulation and the redistribution of composite nanoparticles with gold or silver shells in organs and tissues of mices after the intravenous administration of colloidal solutions of nanoparticles.