Valeri B. Arakelyan

Hydrogen Sensor Made of Porous Silicon and Covered by TiO

Hydrogen sensor working at room and 40degC temperatures made of porous silicon covered by the TiO2-x or ZnO(Al) thin film was realized. Porous silicon layer was formed by electrochemical anodization on a p- and n-type Si surface. Thereafter, n-type TiO2-x and ZnO(Al) thin films were deposited onto the porous silicon surface by electron-beam evaporation and magnetron sputtering, respectively. Platinum catalytic layer and Au electric contacts were for further measurements deposited onto obtained structures by ion-beam sputtering. The sensitivity of manufactured structures to 1000-5000 ppm of hydrogen, propane-butane mixture, and humidity was studied. Sensitivity of obtained structures was determined as ratio of the resistivity of structures in the presence of investigated gas to that in air. Results of sensitivity measurements showed that it is possible to realize a hydrogen nanosensor, resistivity of which can be decreased up to 2.5 times at room temperature and four times at 40degC for the Pt/TiO2-x/PS structure, as well as two times for the Pt/ZnO(Al)/PS structure at 40degC at 5000 ppm hydrogen concentration, respectively. Both structures have the recovery and response time of approximately 20 s and rather high durability and selectivity to hydrogen gas.

_{2-{\rm x}}

Abstract Correlation functions and spectral density of the number of molecules of ligand bound to DNA are calculated theoretically. Kinetics of rates of formation and decomposition of the complex are determined by calculating the dependence of correlation function on concentration of ligand in solution. The analysis of spectral density allows to distinguish “fast” and “slow” adsorption of ligands on macromolecule.

or ZnO

Abstract In the present work fluctuations of number of ligands adsorbed on macromolecule are investigated. We have taken into account the adsorption and desorption of ligands under the circumstance of some adsorption centers fluctuations affected by medium fluctuation. The correlation function and spectral density of number of ligands adsorbed on macromolecule are calculated. The properties of these fluctuations which allow identifying a noisemaker are determined. It has been shown, that “fast” and “sluggish” adsorption can be distinguished by properties of dispersion and spectral density. It has been also shown, that comparison of experimental and theoretical correlation functions (or spectral densities) allows to calculate constants of ligand—adsorption center binding and unbinding.

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In this paper, a method that allows to analyze the binding curves of ligand (EtBr) with single-stranded (ss) and double-stranded (ds) DNA, when there are at least two modes of ligand binding to DNA at small fillings has been proposed. The obtained experimental binding curves for EtBr–ssDNA and EtBr–dsDNA have two clearly expressed linear regions. These curves were analyzed by two modes: Experimental points on linear regions were described by two different lines and all experimental points were described by single curve. It was revealed that the description by single curve permits obtaining more precise data of binding parameters (i.e. binding constant and number of base pairs that bind one ligand molecule). Moreover, the proposed method permits determining the value of proportion of binding sites of each binding mode.

Al

Abstract Ligand binding to nucleic acids (NA) is considered as a stationaiy Markov process. It is shown that the probabilistic description of ligand-NA binding allows one to describe not only the kinetics of the change of number of bound ligands at arbitrary fillings but also to calculate stationaiy values of the number of bound ligands and its dispersion. The general analysis of absoiption isotherms and kinetics of ligand binding to NA make it possible to determine of rate constants of ligand-NA complex formation and dissociation.

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In the present work, the adsorption kinetics of extended ligands on DNA duplexes at small fillings when molecules of DNA duplexes are on the underlayer within diffusion layer has been investigated. Both diffusion of ligands in solution (diffusion stage) and adsorption of ligands (kinetic stage) are taken into consideration at adsorption of ligands on DNA duplexes. Nonlinear system of differential equations describing adsorption of ligands where not only diffusion stage but also kinetic stage is taken into account, is obtained, moreover the equations allow localizing duplexes in arbitrary place within diffusion layer. Numeric solution of the equations makes possible to investigate the filling kinetics of DNA duplexes by ligands depending on parameters controlling adsorption process. It has been shown that depending on relation between adsorption parameters different kinetic regimes of adsorption – kinetic, complex, and diffusion regimes may be realized.

Thin Film

Abstract Simultaneous formulation binding and structure modification of the binding site leads to binding process that can be analyzed within the framework of the non-linear theory of dynamic systems. Such an approach allows us to obtain several properties of the binding center: plurality of stationary (stable and unstable) states at binding, recognition of bistable and hysteretic binding modes. It is also shown that adsorption centre deformation leads to a S-shaped adsorption curve.

Determination of Constant Rates of Adsorption of Ligand on DNA: Analysis of Correlation Functions

The average, variance, correlation function and the spectral density of ligand–receptor complexes in the presence of the external Langevin noise are calculated and their characteristics are defined. The analysis of the experimental data using the formulas derived in this work enables one to obtain a new information on the process of forming of ligand–receptor complex, namely, the constants rates of formation and the decay of the ligand–receptor complex.

Adsorption of Ligands on Macromolecules in the Fluctuating Medium

Many water-soluble cationic porphyrins are known to be prospective chemotherapeutics and photosensitizers for cancer treatment and diagnosis. The physicochemical properties of porphyrins, in particular their interactions with membranes, are important determining factors of their biological activity. The influence of cationic meso-tetra-[4-N-(2′-hydroxyethyl) pyridyl] porphyrin (H2TOEtPyP) on the stability and conductivity of bilayer lipid membranes (BLMs) was studied. H2TOEtPyP4 porphyrin was shown to decrease the stability of BLMs made of a mixture of DOPS and DPPE (1:1) in an electric field because of a reduction of line tension of spontaneously formed pore edges in the BLM. The presence of cationic porphyrin was found to reduce BLM surface tension. This effect was enhanced with increasing porphyrin concentration. H2TOEtPyP4 increased the probability of spontaneous pore formation. Further investigating the cyclic current-voltage characteristics of BLMs allowed determining the electrical capacity and conductivity of BLMs in the presence of H2TOEtPyP4 porphyrin. It was shown that in the presence of cationic porphyrin the electrical capacity as well as conductivity of the BLM increases.

Analysis of experimental binding curves of EtBr with single- and double-stranded DNA at small fillings

Fluctuations of the number of ligands adsorbed on macromolecules are considered in the case when the number of ligands in the solution fluctuates under the action of fluctuations of the external medium (external noise). For the case of small filling, the multiplicative type of stochastic differential equation is obtained, describing the time variation of the number of ligands adsorbed on macromolecules. The isotherm of adsorption of ligands on DNA is obtained. It is shown that at small ligand concentrations, for some relations between adsorption parameters and the intensity of the external noise, no macromolecule adsorption of ligands takes place.