S. G. Dorofeev

Fluorescent immunolabeling of cancer cells by quantum dots and antibody scFv fragment

Semiconductor quantum dots (QDs) coupled with cancer-specific targeting ligands are new promising agents for fluorescent visualization of cancer cells. Human epidermal growth factor receptor 2/neu (HER2/neu), overexpressed on the surface of many cancer cells, is an important target for cancer diagnostics. Antibody scFv fragments as a targeting agent for direct delivery of fluorophores offer significant advantages over full-size antibodies due to their small size, lower cross-reactivity, and immunogenicity. We have used quantum dots linked to anti-HER2/neu 4D5 scFv antibody to label HER2/neu-overexpressing live cells. Labeling of target cells was shown to have high brightness, photostability, and specificity. The results indicate that construction based on quantum dots and scFv antibody can be successfully used for cancer cell visualization.

Preparation of copper-doped CdSe nanocrystals

Sols of stabilized copper-doped CdSe nanocrystals in a nonpolar high-boiling solvent have been synthesized using cadmium oleate, copper stearate, and trioctylphosphine selenide as starting reagents. The average size of the nanocrystals is 2.8–2.9 nm, with a 10% variance, as evaluated from their absorption spectra. The samples show excitonic luminescence and bright near-IR (700–900 nm) luminescence with a lifetime on the order of 0.5–1 μs. The luminescence spectroscopy data are consistent with the assumption that the copper distribution over the nanocrystals follows Poisson’s law. The average copper content of the samples is 0.1–2 atoms per nanocrystal.

Impedance spectroscopy of ultrafine-grain SnO2 ceramics with a variable grain size

The impedance spectra of nanocrystalline SnO2 ceramics with an average grain size d ranging from 3 to 43 nm were investigated in the frequency range 1–106 Hz at temperatures from 25 to 300°C in a dry oxygen atmosphere. Analysis of the experimental data by the graphoanalytical method made it possible to separate the contributions of grain bulk and grain boundaries to the conductivity. It is shown that the samples investigated can be arbitrarily divided into two groups with respect to the character of their conductivity. For the samples with an average grain size d < 25 nm, the charge transfer processes are almost completely determined by the grain boundaries. In samples with a larger grain size, the contribution of grain bulk to the conductivity is comparable with that of grain boundaries.

PbTe-VTe2 phase diagram and properties of (PbTe)1 − x(VTe2)x solid solutions

The T-x phase diagram along the PbTe-VTe2 join of the Pb-V-Te system has been studied. Vanadium-doped lead telluride crystals have been grown, and the longitudinal vanadium and carrier profiles in the crystals have been investigated. The temperature dependences of resistivity for the crystals lend support to the conclusion drawn earlier that PbTe〈V〉 is in a semi-insulating state at low temperatures. The crystals offer a high 20-K electron mobility, on the order of 105 cm2/(V s), which attests to high electrical homogeneity of the material and stabilization of the Fermi level.

IR-active vibrational modes of CdTe and CdSe colloidal quantum dots and CdTe/CdSe core/shell nanoparticles and coupling effects

The frequencies of the vibrational modes of CdTe and CdSe quantum dots and CdTe/CdSe core/shell nanoparticles prepared by the colloid chemistry method are determined using IR transmission and IR reflection spectroscopy. The experimental IR transmission spectrum of CdTe and CdSe nanocrystals exhibits a broad minimum located between the frequencies of the transverse optical (TO) and longitudinal optical (LO) phonons of bulk CdTe and CdSe crystals. The frequencies of the modes for ensembles of CdTe and CdSe quantum dots are considerably shifted toward lower frequencies as compared to those calculated for single quantum dots. This is explained by the dipole-dipole interaction between quantum dots. The frequencies of modes for the structures with core/shell nanoparticles differ little from the calculated frequencies. This suggests a weakening of the interaction in these structures due to the enhancement of dielectric screening.

Synthesis and properties of vanadium-doped lead telluride

We have studied a portion of the ternary system Pb-V-Te. Pseudobinary joins have been identified, the vanadium solubility along the V3Te4-PbTe join has been determined, and the lattice parameter of the solid solution has been measured as a function of vanadium content at 800 and 870°C. Six PbTe〈V〉 crystals have been grown by the Bridgman method, and their microstructure and transport properties have been investigated. The results indicate that vanadium in PbTe is not a simple donor: its effect depends on those growth conditions that determine the degree of compensation of the donor effect of vanadium and native defects. PbTe〈V〉 samples have been found to pass into a high-resistivity state on cooling and to be photosensitive. The depth of the vanadium donor level in the band gap of lead telluride has been evaluated.

On the application of thin films of silicon nanoparticles for increasing solar cell efficiency

The effect of thin films of silicon nanoparticles (nc-Si), deposited onto the front surface of single-crystal silicon solar cells, on their conversion efficiency is studied. The thin films are grown using non-luminescent silicon nanoparticles with an average diameter of 12 nm with SiOx (0 ≤ x ≤ 2) shells and silicon nanoparticles 2 nm in diameter with organic shells of octadecene, which exhibit photoluminescence in the red spectral region. It was found that nc-Si film deposition increases the solar-cell conversion efficiency by 12% with respect to the initial value. An analysis of the current-voltage characteristics and reflectance spectra of solar cells allows the conclusion that the increase in the conversion efficiency is controlled by the passivation of defects on the front surface of the solar cell by nanoparticles and a decrease in the light reflectance of this surface.

Immobilization of luminescent nanosilicon in a microfine polytetrafluoroethylene matrix by means of supercritical carbon dioxide

With the use of supercritical carbon dioxide (SC-CO2), the matrix immobilization of photoluminescent silicon nanocrystals (nc-Si) in polytetrafluoroethylene microparticles (mp-PTFE) is performed, which leads to the formation of mp-PTFE/nc-Si photoluminescent nanocomposite containing ∼103–104 nc-Si particles per mp-PTFE particle (1–2 μm in size). This approach is based on the effect of polymer swelling in SC-CO2, efficient SC-CO2-assisted transport of nanoparticles into the internal free volume of the polymer, and contraction of the nanocomposite after the release of CO2, an effect that prevents the subsequent agglutination of nanoparticles. Particles of nc-Si photoluminescent in the visible spectrum were synthesized from silicon suboxide powder (SiOx, x ≈ 1) heated at various temperatures within 25–950°C and then etched in concentrated hydrofluoric acid. The hydrosilylation procedure was used to graft 1-octadecene molecules to the surface of nc-Si particles. As a result, the photoluminescence intensity of nc-Si increased substantially. According to TEM images and small angle X-ray scattering data, the maximum size of nc-Si particles did not exceed 5 nm and 7 nm, respectively, and the core of these nanoparticles consisted of crystalline silicon. The structure and spectral properties of the initial nc-Si particles and synthesized mp-PTFE/nc-Si photoluminescent nanocomposite microparticles were studied.

Gas sensitivity of etioporphyrin metal complexes in thin films

It is shown that porphyrin metal complexes have the potential for the creation of various gas sensors; the gas sensing properties of the materials on their basis change upon the replacement of the central metal atom and substituents in the porphyrin core. Films of etioporphyrin-II were prepared by vacuum deposition onto a front shaft system of electrodes on a pyroceramic support. Calibration dependences of the analytical signal (conductivity) on the concentration of ammonia were obtained. It was found that UV irradiation on the sensor layer enhances the sensitivity of ammonia determination. Relative sensitivities of thin films based on Co(II), Ni(II), Cu(II), Zn(II), Pd(II) and Pt(II) etioporphyrin complexes in the temperature range from 303 K to 423 K and ammonia concentrations from 1.5 to 75 mg/m3 were determined. The relative sensitivity attains a maximum (0.8) at an ammonia concentration of 7.5 mg/m3 for the Co(II) etioporphyrin at 333 K in a dark mode, or at 303 K and under UV irradiation (λ = 406 nm, P = 1 mW). An experimental setup was assembled that allowed measurements at the controlled temperature and humidity of the gas and its mixtures with inert gases or air. The conditions of ammonia detection were optimized.

Sensitization of ZnO nanorods with CdSe quantum dots

We have optimized the low-temperature growth of aligned arrays of zinc oxide nanorods of controlled length and diameter on conductive substrates. Varying the solution concentration and growth time, we were able to tune the nanorod diameter and length in the ranges 40–600 nm and 0.5–15 μm, respectively. The grown zinc oxide nanorods were photosensitized with CdSe quantum dots (QDs) in an oleic shell, which was replaced by pyridine. We studied the optical and transport properties of the ZnO nanorod arrays, with and without CdSe QDs on their surface. The current-voltage characteristics of the ZnO nanorod arrays with CdSe QDs are significantly influenced by illumination with light at a wavelength under the absorption band of the QDs, which points to effective interaction between the QDs and ZnO matrix.