Evgenia Slyusareva

Spectral study of fluorone dyes adsorption on chitosan-based polyelectrolyte complexes.

Polyelectrolyte complexes of the chitosan-chondroitin sulfate and chitosan-hyaluronate polycation-polyanion pairs were synthesized and characterized as potential dye adsorbents at different pH levels. Equilibrium isotherm analysis was applied to investigate the efficiency and the mechanism of the adsorption of fluorone dyes (fluorescein, eosin Y, erythrosin B) on the synthesized complexes. The inefficiency of the fluorescein adsorption was proved by two different quantitative spectroscopic methods. The adsorption isotherm for both eosin Y and erythrosin B was adequately described in terms of the Langmuir-Freundlich model. The observed room-temperature phosphorescence of the adsorbed erythrosin B was attributed to the surface inhomogeneity of the synthesized complexes. The revealed variation in the adsorption properties of fluorone dyes was related to the differences in their ionic forms as well as in their polarity and hydrophobicity.

The role of energy transfer in bioluminescence quenching by xanthene dyes.

The paper reports the experimental results of bioluminescence quenching in the coupled enzyme system NADH:FMN-oxidoreductase-luciferase in the presence of xanthene dyes (fluorescein, eosin Y, erythrosin B) featured by the rate constants of intersystem crossing. From the spectral data and with the help of kinetic model the rate constants of energy transfer from emitter to dye were determined (2.9 x 10(12)-6.5 x 10(13) M(-1) s(-1)) and the emitter lifetime was estimated (1.2-2.7 ns). The calculated rate constants of energy transfer in a series of xanthene molecules are higher than the diffusion-controlled constants. The rate constants of energy transfer correlate with the probability of intersystem crossing of a dye. The combined analysis of emitter fluorescence quenching and acceptor fluorescence enhancement indicates that the significant bioluminescence intensity decrease in the presence of xanthene dyes is determined by both the quenching processes via the energy transfer and the inhibition of bioluminescent reaction.

Synthesis and Characterization of Chitosan‐Based Polyelectrolyte Complexes Doped with Xanthene Dyes

Biocompatible chitosan-based polyelectrolyte complexes (PECs) doped with xanthene dyes (fluorescein, eosin Y, erythrosin B, rhodamine 6G) were synthesized and characterized by scanning electron microscopy, dynamic light scattering, zeta potential measurements, and absorption and luminescence (including polarized, time-resolved, and phosphorescence) spectroscopy. The results are discussed in terms of the mechanism and rigidity of dye-PEC binding, the heavy-atom effect in dyes and PEC stability. Eosin Y is found to be the optimal dopant, providing both a high dye content in PECs and a high quantum yield of fluorescence.

Förster resonance energy transfer between quantum dots and dye immobilized in biopolymer particles

We used high adsorption properties of the cationic biopolymer chitosan to synthesize colloidal polymer particles (average size about 0.3 μm) with immobilized CdTe quantum dots (QDs) and organic dye (erythrosin B). A high local concentration of fluorophores bound to the particles (about 10–3 M), as well as a wide overlap of their optical spectra result in an efficient (up to 80%) Förster resonance energy transfer (FRET) from QDs ensembles to dye molecules. The FRET was registered by both steady-state (quenching of the donor and enhancement of the acceptor fluorescence) and time-resolved methods (decreasing of donor lifetime). The dependence of the transfer efficiency on acceptor concentration was analyzed within the scope of the Förster theory extended for the case of multiple energy transfer configuration. The average distances between the donor and acceptor as well as local concentration of fluorophores within particles were determined. It was demonstrated that the synthesized particles can be used as FRET-based sensitive probes for inter-fluorophore distance calculation within the range of 4 ÷ 9 nm.

Spectroscopic behavior of pyrrolanthrone and its derivative in aprotic and protic solvents

Recently synthesized pyrrolanthrone, naphtho[1,2,3-cd]indole-6(2H)-one (PyAn), and its water-soluble derivative, 3(naphtho[1,2,3-cd]indole-6(2H)-one-2-yl) sodium propylsulfonate, are very promising for anticancer therapy due to both the fluorescent and cytotoxic properties. The present study is focused on the spectroscopic analysis of solvent effects in PyAn and its derivative. An increase of the solvent polarity results in the bathochromic shift in emission and absorption spectra that indicates the involvement of ππ*-type transition. The double linear correlation of Stokes shift with bulk solvent polarity functions (in terms of Lippert’s, Bakhshiev’s and Chamma-Viallet’s models) and microscopic solvent polarity parameter ( ) 30 N ET for aprotic and protic solvents is observed. Both general and specific solvent effects are revealed for the solute-solvent systems. Fluorescence quantum yield, fluorescence lifetime and excited-state dipole moment were defined for PyAn and its derivative in different solvents for the first time. The obtained information is of a great importance for the characterization of intermolecular interactions of drugs with biomolecules for the development of new drug delivery systems.

Laser-induced Interaction of Multilevel Quantum Dots

A theoretical model is developed for describing the laser-induced interaction of a pair of multilevel semiconductor quantum dots. Spectral dependencies of interaction energy are calculated in dipole-dipole approximation for a pair of CdSe quantum dots in a quasi-resonant laser field, for cases of two identical quantum dots and those with differing transition wavelengths. Interaction energy of pair of multilevel quantum dots in the long-wavelength potential well is much higher than that of pair of two-level quantum dots. The increase of difference of resonance wavelengths of two interacting quantum dots leads to decrease of the potential well depth.

Synthesis and characterization of chitosan-based polyelectrolyte complexes, doped by quantum dots

Doping of polymer particles by a fluorophores results in the sensitization within the visible spectral region becoming very promising materials for sensor applications. Colloids of biocompatible chitosan-based polyelectrolyte complexes (PECs) doped with quantum dots (QD) of CdTe and CdSe/ZnS (with sizes of 2.0-2.4 nm) were synthesized and characterized by scanning electron microscopy, dynamic light scattering, ζ-potential measurements, absorption and luminescence (including time-resolved) spectroscopy. The influence of ionic strength (0.02-1.5 M) on absorption and photoluminescence properties of encapsulated into PEC and unencapsulated quantum dots was investigated. The stability of the emission intensity of the encapsulated quantum dots has been shown to be strongly dependent on concentration of quantum dots.