Long path DOAS measurements of atmospheric pollutants concentration

A differential optical absorption spectroscopy gas-analyzer consisted of a coaxial telescope, a spectrometer, an analyzer and retroreflector was successfully tested. A high pressure 150-W Xe arc lamp was employed as a light source. In order to record the spectra, a monochrometer with a grating and photodiode array was used. Gas analyzer spectral data bank includes more than 35 moleculas absorbed in UV spectral region. The measured absorption spectra were evaluated by using a least-squares fit to determine the average mixing ratio of each species in the atmosphere. As a result of experiments time series of concentrations of gases polluting the atmosphere were trace measured. Minimally detected concentration on pathlength 480 m is the unit of ppb at the time of accumulation of 2 min. The results of the field test measurements of pollutants in Tomsk city are presented

Two-stage ZnS Shell Coating on the CuInS2 Quantum Dots for Their Effective Solubilization

High-precision diagnostics is one of the necessary conditions for effective treatment of diseases. Bioimaging is one of the most promising modern methods of tumor diagnosis. High-quality luminophores are necessary for effective bio-imaging. CuInS2(CIS) quantum dots (QDs) are very promising luminophores for these applications due to their low toxicity and long-term stability of their properties. Two batches of CIS QDs with different positions of the luminescence maximum have been obtained. The position of the luminescence maximum can be controlled by changing the Cu to In ratio; a decrease in this ratio cause a blue shift of the luminescence. The standard procedure of CIS synthesis yields QDs covered with thiols, which form strong bonds with the surface and prevent the ligand exchange; hence, it is very hard to adapt CIS QDs for biological tasks using the standard hydrophobic to hydrophilic ligand exchange procedure. We have developed a two-stage shell coating procedure yielding CIS QDs covered with amines, which is suitable for ligand exchange; hence,the resultant QDs can be adapted for modern biological and medical applications. Keywords: Quantum dots, CuInS2, solubilization

Magnetic properties of pure and Gd doped EuO probed by NMR

An Eu NMR study in the ferromagnetic phase of pure and Gd doped EuO was performed. A complete description of the NMR lineshape of pure EuO allowed for the influence of doping EuO with Gd impurities to be highlighted. The presence of a temperature dependent static magnetic inhomogeneity in Gd doped EuO was demonstrated by studying the temperature dependence of the lineshapes. The results suggest that the inhomogeneity in 0.6% Gd doped EuO is linked to colossal magnetoresistance. The measurement of the spin-lattice relaxation times as a function of temperature led to the determination of the value of the exchange integral J as a function of Gd doping. It was found that J is temperature independent and spatially homogeneous for all the samples and that its value increases abruptly with increasing Gd doping.Comment: 14 pages, 10 figures, to be published in Physical Review

Laser Irradiation as a Tool to Control the Resonance Energy Transfer in Bacteriorhodopsin–Quantum Dot Bio-Nano Hybrid Material

 Bacteriorhodopsin (BR) is a natural photosensitive protein which can be considered promising in photovoltaics and optoelectronics because of its ability to produce a pronounced electrochemical response and controllably change its absorption spectrum under light excitation. However, its applicability is limited by its narrow absorption spectrum and low values of the absorption cross sections. Semiconductor quantum dots (QDs), which have high one- and two-photon absorption cross-sections in a UVand NIR spectral regions, respectively, can significantly improve the light sensitivity of BR by means of Förster resonance energy transfer (FRET) from QD to BR. In this work, we demonstrate the possibility to control the efficiency of FRET from QD to BR within electrostatically bound complexes of QD and purple membranes (PM) containing BR. We show that laser irradiation of QDs at different wavelengths leads to distinct changes (rise or decrease) of QD luminescence quantum yield (QY) without changing of QD structure. Such photo-induced changes in the QY of QD lead to a corresponding change in the efficiency of FRET. We have estimated efficiencies of FRET from QD to BR in the PM complexes composed of irradiated and non-irradiated QDs and found the increase in FRET efficiency with irradiated QDs

Efficient Encoding of Matrix Microparticles with Nanocrystals for Fluorescent Polyelectrolyte Microcapsules Development

Polyelectrolyte microcapsules development and further use as specific carriers for drug molecules, fluorescent dyes, and metal nanoparticles is a promising approach to designing theranostic agents. Semiconductor nanocrystal quantum dots exhibiting size-dependent optical properties, a high photostability, and optimal fluorescent properties can be advantageous over classical organic fluorophores. The results of elaboration of efficient encoding of matrix microparticles with nanocrystals for development of fluorescent polyelectrolyte microcapsules and the characteristics of the obtained encoded microbeads are demonstrated. Keywords: Semiconductor nanocrystals; encoding of matrix microbeads; theranostic agents, polyelectrolyte microcapsules, layer-by-layer technique

The Effect of Quantum Dot Shell Structure on Fluorescence Quenching By Acridine Ligand

The current strategy for the development of advanced methods of tumor treatment focuses on targeted drug delivery to tumor cells. Quantum dot (QD) - semiconductor fluorescent nanocrystal, conjugated with a pharmacological ligand, such as acridine, ensures real-time tracking of the delivery process of the active substance. However, the problem of QD fluorescence quenching caused by charge transfer can arise in the case when acridine is bound to the QD. We found that QD shell structure has a defining role on photoinduced electron transfer from QD on acridine ligand which leads to quenching of QD photoluminescence. We have found that multishell CdSe/ZnS/CdS/ZnS QD structure provides minimal reduction of photoluminescence quantum yield at minimal shell thickness compared to classical thin ZnS or “giant” shells. Thus, CdSe/ZnS/CdS/ZnS core/multishell QD could be an optimal choice for engineering of small-sized acridine-based fluorescent labels for tumor diagnosis and treatment systems. Keywords: Quantum dot, photoluminescence quenching, DNA ligand, acridine derivative

Optical Properties of Core-Multishell Quantum Dots

During the past decade, colloidal semiconductor nanocrystals or quantum dots (QDs) have become not only a subject of interesting fundamental research, but also a product for real-life applications. Intense activities devoted to enhancement of QDs photoluminescence (PL) quantum yield (QY), starting from early attempts to deposit protective ZnS shells atop CdSe cores, have resulted in novel designs of core-shell QDs with 100% PL QY. In this work we present a detailed analysis of optical properties of core-“multishell” (MS) QDs, whose physical structure is specifically designed to attain maximum localization of excited charge carriers inside luminescent cores, and thereby to achieve 100% PL QY. We have produced samples of core-MS QDs having 3 to 7 shell monolayers, studied the evolution of optical transitions in such QDs during the process of shell deposition, and analyzed the effects of shell thickness on the optical properties of finally obtained QDs. Specifically, studies of PL lifetimes have revealed the possibility of alternative emission mechanism, based on delayed charge carrier transfer from excited outer CdS layer of the multishell into CdSe cores. Keywords: quantum dots, core-shell, multishell, SILA

Highly Stable, Water-Soluble CdSe/ZnS/CdS/ZnS Quantum Dots with Additional SiO2 shell

Quantum dots (QDs) are fluorescent nanocrystals extensively used today in research and applications. They attract much interest due to the high photostability and fluorescence quantum yields close to 100%. The best QDs are made by synthesis in organic media, and they have to be transferred into aqueous solutions if biomedical applications are concerned. An advanced method for rendering QDs water-soluble is to coat them with hydrophilic SiO2 -layer. However, growing a silica shell with a predetermined thickness is a problem, because uncertain values of the molar extinction coefficients (ε) of core/shell QDs made it impossible to calculate precise yields of the chemical reactions involved. Here we suggest an approach to solving this problem by constructing the structural models of per se and silica-coated QDs followed by measuring ε in a course of the QD synthesis, thus carrying out precise quantitative reactions. Proceeding in such a way, we prepared the CdSe/ZnS/CdS/ZnS QDs with the structure predicted by the model and coated by silica shell. Prepared QDs are characterized by a narrow size distribution and the same fluorescence parameters as the original QDs in the organic medium. Developed approach permitted efficient QDs water-solubilisation and preparation of stable nanoparticles for plethora of biomedical applications.     Keywords: Quantum dots, QD, silica shell, core-shel

The Bean-Livingston barrier at a superconductor/magnet interface

The Bean-Livingston barrier at the interface of type-II superconductor/soft-magnet heterostructures is studied on the basis of the classical London approach. This shows a characteristic dependence on the geometry of the particular structure and its interface as well as on the relative permeability of the involved magnetic constituent. The modification of the barrier by the presence of the magnet can be significant, as demonstrated for a cylindrical superconducting filament covered with a coaxial magnetic sheath. Using typical values of the relative permeability, the critical field of first penetration of magnetic flux is predicted to be strongly enhanced, whereas the variation of the average critical current density with the external field is strongly depressed, in accord with the observations of recent experiments.Comment: RevTeX 4; revised version; accepted in Journal of Physics: Condensed Matte

Defining Substance Use Disorders: Do We Really Need More Than Heavy Use?

Aims: The aim of the study was to explore whether the concept of heavy substance use over time can be used as definition of substance use disorder. Methods: Narrative review. Results: Heavy use over time clearly underlies the neurobiological changes associated with current thinking of substance use disorders. In addition, there is evidence that heavy use over time can explain the majority of social problems and of burden of disease (morbidity and mortality). A definition of substance use disorders via heavy use over time would avoid some of the problems of current conceptualizations, for instance the cultural specificity of concepts such as loss of control. Finally, stressing the continuum of use may avoid the high level of stigmatization currently associated with substance use disorders. Conclusion: ‘Heavy substance use over time' seems to be a definition of substance use disorders in line with results of basic research and epidemiology. Additionally, it reduces stigmatization. This approach should thus be further explore