Quantum Dot Conjugates in Functional Imaging and Highly Sensitive Biochemical Assays

Semiconductor quantum dots (QDs) are characterized by orders of magnitude higher multiphoton linear absorption cross-sections compared with conventional organic dyes. Combined with the QD photoluminescence quantum yield approaching 100%, this fact opens new prospects for the two-photon functional imaging of QDs tagged with highly specific recognition molecules, thus permitting high-quality images with a very low autofluorescence contribution to be obtained. Additionally, unique photostability of QDs enables signal accumulation and significant enhancement of the sensitivity of routine biochemical and immunohistochemical assays to be obtained when the conjugates of QDs, instead of organic dyes, are used. Keywords: Nanocrystals, semiconductor quantum dots, FRET, single-domain antibodies, imaging, multiphoton

Preparation of Freestanding Porous Silicon Photonic Crystals

Nowadays, the photonic crystals are of great interest and are widely used in photonics, biosensing, optoelectronics and other fields of research. The one-dimensional photonic crystals manufactured on the basis of porous silicon were proved to be the most suitable for applications due to their high sorption ability, large surface area, easiness of fabrication, and possibility to precisely control porosity and refractive index during electrochemical etching. However, the sensitivity of various kinds of gas and biological sensors as well as the performance of solar cells and other devices on the basis of porous silicon structures may be significantly increased by detaching the structures from the substrate. Here, we have developed and investigated the fabrication procedure of freestanding one-dimensional photonic crystals on the basis of porous silicon with the use of electropolishing method followed stabilization of freestanding porous silicon photonic structures through their oxidation. We have demonstrated that the developed and applied lift-off procedure does not violate the morphology and the photonic properties of the samples. Keywords: Porous silicon, photonic crystals, microcavity, thin films, freestanding photonic crystals

Porous Silicon Photonic Crystal as a Substrate for High Efficiency Biosensing

Photonic crystals offer great possibilities for the improvement of performance of different kinds of devices. Due to the ability to control the light propagation and to change optical properties via interaction with the media photonic crystals have been widely used to increase the sensitivity of biosensing in many experimental setups. Among them some of the most interesting for practical applications are one-dimensional porous silicon photonic crystals. They could be easily fabricated, have big surface area, high sorption abilities, and have been shown to be able to change the emission of embedded luminophores. In this study we have fabricatedand performed the comprehensive investigation of the properties of hybrid system consisting of the porous silicon one-dimensional photonic crystals embedded with semiconductor quantum dots as the luminophores. We have demonstrated the ability of these systems to enhance the photoluminescence of luminophores and serve as the substrate for the high efficient biosensing. Keywords: Porous silicon, microcavity, quantum dots, luminescence enhancemen

Modeling and Optimization of the Porous Silicon Photonic Structures

Photonic crystals and optical devices based on them are of great interest nowadays and are widely used in photonics, optoelectronics, and biosensing. One of the most practically using materials to fabricate one-dimensional photonic crystal is porous silicon due to the simple fabrication process, high porosity and ability to select precisely the refractive index by controlling the porosity. It has already been shown as the suitable material to be used as an element of many photonic devices including gas sensors and biosensors. However, because of the complicated porous structure, and silicon oxidation, occurring at the atmosphere conditions, optical properties of porous silicon photonic structures need to be stabilized by preventive oxidation. In order to predict eventual optical properties of fabricated photonic structures an adequate modeling should be performed. In our study we have developed a calculation model based on the combination of effective media approximations and transfer matrix method, which could precisely predict the reflection, transmission of the porous silicon photonic structures taking into account the dispersion of the refractive index of silicon and silicon oxide, and the oxidation degree. We also used numerical finite-difference time-domain calculations in order to investigate the luminescent properties of the lumiphores embedded into the porous photonic structure. Keywords: Porous silicon, microcavity, transfer matrix, effective media, FDT

Inverse spectral problems for energy-dependent Sturm-Liouville equations

We study the inverse spectral problem of reconstructing energy-dependent Sturm-Liouville equations from their Dirichlet spectra and sequences of the norming constants. For the class of problems under consideration, we give a complete description of the corresponding spectral data, suggest a reconstruction algorithm, and establish uniqueness of reconstruction. The approach is based on connection between spectral problems for energy-dependent Sturm-Liouville equations and for Dirac operators of special form.Comment: AMS-LaTeX, 28 page

QSPR modeling aqueous solubility of polychlorinated biphenyls by optimization of correlation weights of local and global graph invariants

Aqueous solubilities of polychlorinated biphenyls have been correlated with topological molecular descriptors which are functions of local and global invariants of labeled hydrogen filled graphs. Morgan extended connectivity and nearest neighboring codes have been used as local graph invariants. The number of chlorine atoms in biphenyls has been employed as a global graph invariant. Present results show that taking into account correlation weights of global invariants gives quite reasonable improvement of statistical characteristics for the prediction of aqueous solubilities of polychlorinated biphenyls.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

«Muslim matter» in the mirror of public discussion (XIX - beginning of XX century)

The relevance of the studied problem is determined by the socio-political processes that have embraced the modern Islamic world, connected with the substantial politicization of the Muslim community, religious revival movements and the spread of radical currents. The paper is aimed at studying the public debate in Russia (XIX-early XX century) regarding the future of domestic Muslims. The leading approach to the study of this problem is the concept that modernization attempts in Russia had compensatory nature and were aimed at strengthening the imperial system. Based on the study of the works by the experts of the "Muslim matter”, the authors came to the conclusion that the public discussion arrived at a view that it is necessary to strengthen the spiritual and cultural assimilation of foreigners on the ways of activating both administrative and cultural methods. Reliability of the results of the study is determined by the authors' appeal to a representative sample and analysis of the works by Russian scientists and publicists, who most clearly reflected the position of their socio-political group regarding the future of the Muslim community in Russia. Along with the opinions of academic orientalists and Islamologists, the views of representatives of the scientific missionary circles, Muslim modernists, revolutionary democrats, etc. are presented. The materials of the paper can be useful for further development of scientific problems on the history of Islam and Muslim peoples, as well as the history of culture and public thought of the peoples of Russia.Keywords: history, social studies, Islamic studies, Russian empire, "Muslim matter", publicdiscussion

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

QSPR modeling aqueous solubility of polychlorinated biphenyls by optimization of correlation weights of local and global graph invariants

Aqueous solubilities of polychlorinated biphenyls have been correlated with topological molecular descriptors which are functions of local and global invariants of labeled hydrogen filled graphs. Morgan extended connectivity and nearest neighboring codes have been used as local graph invariants. The number of chlorine atoms in biphenyls has been employed as a global graph invariant. Present results show that taking into account correlation weights of global invariants gives quite reasonable improvement of statistical characteristics for the prediction of aqueous solubilities of polychlorinated biphenyls.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta