Svetlana L. Yefimova

Specificity of Cyanine Dye L-21 Aggregation in Solutions with Nucleic Acids

Optical spectroscopy experiments were used to study the features of cyanine dye 3,3′-dimethyl-9-(2-thienyl)-thiacarbocyanine iodide (L-21) aggregation in binary solutions DMF:Tris–HCl buffer (pH = 8) containing nucleic acids (DNA or RNA). The appearance of absorption and luminescence bands associated with J-aggregates and dimers that are formed within the minor groove of DNA has been observed. The model of L-21 J-aggregate structure is proposed. It has been found that dimers are the building blocks of L-21 J-aggregates. Disorientation in dimers caused by the minor groove curvature is reason of observation of Davydov splitting in absorption spectrum of L-21 J-aggregates. In the solution containing DNA the absorption and luminescence bands of L-21 J-aggregates exhibit the specific properties that allows the dye L-21 to be used as a fluorescent probe for DNA detection.

Microspectroscopic Study of Liposome-to-cell Interaction Revealed by Förster Resonance Energy Transfer

We report the Förster resonance energy transfer (FRET)-labeling of liposomal vesicles as an effective approach to study in dynamics the interaction of liposomes with living cells of different types (rat hepatocytes, rat bone marrow, mouse fibroblast-like cells and human breast cancer cells) and cell organelles (hepatocyte nuclei). The in vitro experiments were performed using fluorescent microspectroscopic technique. Two fluorescent dyes (DiO as the energy donor and DiI as an acceptor) were preloaded in lipid bilayers of phosphatidylcholine liposomes that ensures the necessary distance between the dyes for effective FRET. The change in time of the donor and acceptor relative fluorescence intensities was used to visualize and trace the liposome-to-cell interaction. We show that FRET-labeling of liposome vesicles allows one to reveal the differences in efficiency and dynamics of these interactions, which are associated with composition, fluidity, and metabolic activity of cell plasma membranes.

Manifestation of Exciton-Lattice Interaction in J-Aggregates

The inverse correlation between the exciton-lattice interaction strength and the exciton delocalization length is shown for dielectric organic nanoclusters – J-aggregates. Since the exciton delocalization length defines all optical properties of J-aggregates, it allows one to control them via the exciton-lattice interaction. We demonstrate the exciton self-trapping suppression in amphi-PIC J-aggregates as a result of the exciton-lattice interaction weakening due to the formation of a surfactant shell around J-aggregates. The control over optical properties via the exciton-lattice interaction for other types of J-aggregates is discussed.

Mitochondrial potential (ΔΨm changes in single rat hepatocytes: The effect of orthovanadate nanoparticles doped with rare-earth elements

Rare-earth-based nanoparticles (NPs) are widely used as fluorescent probes for imaging in vitro and in vivo. One of the challenges that restrain NPs applications in biomedical research is their effect on subcellular structures. In this paper, the ability of lanthanide NPs to affect the cellular oxidative balance and alter the mitochondrial function was analyzed. Since size and shape mutually affect the cellular internalization and intracellular distribution of NPs, the investigations were performed with NPs of spherical (GdYVO4:Eu3+, spindle-(GdVO4: Eu3+ and rod-like (LaVO4: Eu3+ shapes. Quantitative microfluorimetry with JC-1 (5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazolocarbocyanine iodide) as a mitochondrial probe was used for monitoring of the mitochondrial transmembrane potential (ΔΨm) in single living cells. Changes in the ratio of the JC-1 probe fluorescence were used to analyze the NPs effect on ΔΨm. The fastest suppressive effect (within 1 hour) was found for spherical NPs. Gradual lowering of ΔΨm was observed at the exposure of cells within 24 hours for all types of NPs. Exogenous thiols were required for ΔΨm protection. The protective role of exogenous glutathione (GSH) proves that the increase of reactive oxygen species (ROS) formation with depletion of GSH can mediate NPs toxicity. The dynamics of the shape-dependent effect can be explained by the features of NPs transportation into cells.Graphical abstract

Influence of Dye Hydrophobicity on the Efficiency of Fluorescence Resonance Energy Transfer Between Dyes in Surfactant Micelles

The fluorescence resonance energy transfer (FRET) between dyes DiOCn (n = 2, 6, 9, and 18) and DiI in aqueous sodium dodecyl sulfate solutions has been studied using the steady-state fluorescence spectroscopy technique. High values of the Stern–Volmer constant (K SV ) obtained indicate the long-range dipole-dipole interaction between an excited donor DiOCn and a ground-state acceptor DiI. The energy transfer efficiency (E) has been analyzed, by basing on both the donor luminescence quenching and the acceptor luminescence enhancement. An increase in E with the donor hydrophobicity is explained in frames of the Förster theory due to shortening the distance between the donor and the acceptor in a SDS micelle.

Excitation localization effects in nanoscale molecular clusters (J-aggregates)

An analysis of experimental data from low-temperature selective spectroscopy and single J-aggregate spectroscopy reveals a hierarchy of exciton states within the confines of the absorption band of J-aggregates which are formed by relaxation of an excited state. For J-aggregates, which are characterized by substantial static disorder, strongly localized excitons are found in the long-wavelength edge of the absorption band; they have a discrete energy spectrum and jump mobility, and are not subject to strong relaxation. Delocalized spatially extended excitons are excited within the absorption band of the J-aggregates, except at its long-wavelength edge. They are characterized by coherent exciton transport and are the source of self-localized excitons.

Reactive oxygen species generation in aqueous solutions containing GdVO 4 :Eu 3+ nanoparticles and their complexes with methylene blue

It this letter, we report the study of free radicals and reactive oxygen species (ROS) generation in water solutions containing gadolinium orthovanadate GdVO4:Eu3+ nanoparticles (VNPs) and their complexes with methylene blue (MB) photosensitizer. The catalytic activity was studied under UV-Vis and X-ray irradiation by three methods (conjugated dienes test, OH· radical, and singlet oxygen detection). It has been shown that the VNPs–MB complexes reveal high efficiency of ROS generation under UV-Vis irradiation associated with both high efficiency of OH· radicals generation by VNPs and singlet oxygen generation by MB due to nonradiative excitation energy transfer from VNPs to MB molecules. Contrary to that under X-ray irradiation, the strong OH. radicals scavenging by VNPs has been observed.

Excimer Emission of Acridine Orange Adsorbed on Gadolinium-Yttrium Orthovanadate Nanoparticles

Studying the complexes of inorganic nanoparticles – organic dye molecules is of great importance for their theranostics application. In this paper, we report gadolinium-yttrium orthovanadate nanoparticles (VNPs) – Acridine Orange (AO) complex formation in water solutions. To study the interactions between VNPs and AO, the methods of steady-state and time-resolved spectroscopy were used. It was shown that in aqueous solutions containing VNPs, AO aggregation takes place with a sandwich-like stacking of AO molecules in the near-surface layer of VNPs. The VNPs–AO complex formation causes significant changes in the AO fluorescence spectrum, namely, the appearance of a new broad, structureless band in the long-wavelength spectral edge, which was not observed in AO spectrum in a pure water solution. By analyzing of the absorption, fluorescence excitation spectra and fluorescence decay, the static excimer origin of the long-wavelength fluorescence band has been established.

Radioprotective Effect of CeO2 and GdEuVO4 Nanoparticles in “In Vivo” Experiments

In experiments performed in vivo of the irradiation of rats, a strong radioprotective effect of nanoparticles based on orthovanadates of rare earth elements and cerium dioxide was found. The nanoparticles were injected per os by two different schemes - once and during 15 days. For the 15-days scheme of GdEuVO4 nanoparticles injection the survival of animals irradiated with a dose of 6.0 Gy was 100 % during 30 days of observation. Injection of CeO2 nanoparticles also effectively protects the bodies of rats from radiation. For an irradiation with the lethal dose of 7.0 Gy, the radioprotective effect of the nanoparticles is negligible.

Manipulation by optical properties of luminescent ordered organic nanoclusters via exciton-phonon coupling

The way to manipulate by spectral properties of cyanine dye luminescent ordered nanoclusters (J-aggregates) has been demonstrated. It has been observed a surfactant shell formation around the J-aggregates of four different dyes. This leads to exciton delocalization length increasing which causes an exciton self-trapping suppression. The latter results in spectral changes observed.