Effect of molecular sieves on discrimination efficiency of a multisensor gas-analysis system

We investigated the effect of zeolite at the sample input of a gas-analysis system (Electronic Nose) on recognition of volatile molecular mixtures. It is shown that the NaX molecular sieves can remove ketone-type molecules from a gas sample more efficiently than the NaA molecular sieves. A comparison of recognition of four different perfumes, both with and without NaA zeolite at the inlet of a multisensor system, showed that introduction of zeolite reduces responses of all sensors and does not improve recognitio

Polymer films as sensitive coatings for quartz crystal microbalance sensors array

This work reports on the results of investigation of quarts crystal microbalance sensors coated with polybutyl methacrylate and polyvinyl formal/ethylal to wide range of volatile organic compounds. Polymer film coated sensors showed a high sensitivity and an excellent selectivity towards these compounds. Good linearity of the concentration dependence has been obtained in almost all the concentration range of volatile compounds. The detection limit of several analytes was less than 100 ppm

Separate determination of thickness and optical parameters by surface plasmon resonance: accuracy consideration

Reliability and precision of characterization of surface layers by SPR method was evaluated with relation to the experimental conditions and the strategy of extracting the film parameters. Consideration is bound up with sensor applications of SPR phenomenon and focused at problems of separate extraction of optical constants and thickness of the layer and determination of the total quantity of material constituting the surface coverage. Computational scheme for modeling the SPR resonance for multilayer assembly, based on the Abeles matrix formalism, is presented. It is demonstrated that improper choice of the angle range the measurements are taken over may result in ambiguity in determination of the real part of the refractive index n and the film thickness d. Nevertheless, the total quantity of material in the film can be estimated with reasonable accuracy even when correct separate extraction of n and d parameters is hampered by experimental errors and inadequacy of theoretical model of layered system

Multisensor systems for gas analysis: optimization of arrays for classification of pharmaceutical products

In the present work, the use of the cluster analysis method in the “fuzzy logic” concept for the optimization of the cross-selective sensor arrays (“electronic nose”, EN) is considered. This approach enables to purposefully form the sensor arrays with definite chemical functionality optimized for the solution of the specific applied problems. The criteria of the optimization of the sensor response, number and type of the sensor elements are considered with the goal to improve the classification of widely used pharmaceutical products. The optimization of EN array in the kinetic mode and selection of the most informative part of the sensor response enabled to reduce the analysis time, and also the number of sensors in array, to improve the discriminatory capability of the whole array. Being based on the analysis of response kinetic peculiarities, the physical mechanisms determining the peculiarities of adsorption-desorption processes at the interface have been considered

The enhancement of optical processes near rough surface of metals

Last decades the enhancement of optical transitions near metal surface was observed under study the optical processes (luminescence, Raman scattering, IR absorption). The effect consists in an essential increase of the intensity of transition (for example, an effective cross-section increases by factor 10⁵…10¹¹ for Raman scattering and 10…10⁴ for IR absorption) or efficiency of the processes near metal surface (e.g. generation of second harmonic). We have analyzed a various experimental techniques that made it possible to achieve an enhancement in surface enhanced infrared absorption (SEIRA), surface enhanced Raman scattering (SERS), metal-enhanced fluorescence. Under the conditions of our experiment and according to literature data, there was observed enhancement factor which equal to 3…20 for vibrations of various molecular groups in SEIRA. Peculiarity of another optical amplifier, namely, colloidal gold nanoparticles, which were effectively used for enhancement of signal in IR absorption and Raman scattering, metal-enhanced fluorescence, has been studied also. Different roughness of gold surface leads to changes in an enhancement factor. The structural features of bovine serum albumine (BSA) – colloidal gold system and enhancement of guanine that obtained in SEIRA experiment are discussed. Atom force microscopy (AFM) technique was applied to test the roughness of the metal surface. We made an attempt to model the factor of enhancement of electrical field and its frequency dependence for different metal surfaces, and ascertained that silver, gold and copper are the best

Multi-element gas sensor based on surface plasmon resonance: recognition of alcohols by using calixarene films

This work is devoted to development of a multi-element gas sensor based on surface plasmon resonance (SPR) to recognize some alcohols. As sensitive layers capable to change their optical properties when interacting with volatile alcohol molecules, we investigated bulk-porous sorbents – calixarenes (tret-butyl-calix[4,6,8]arenes (С[4]А, С[6]А, С[8]А), tetra-amyl-calix[4] resorchinolaren (C[4]Re). Each calixarene was studied to obtain its kinetic concentration SPR characteristics for interaction with ethanol, isopropanol and penthanol vapors. To realize SPR measurements, the sensitive calixarene films (d ∼ 100 nm) were deposited on a gold film (d ∼ 45 nm) by using the method of thermal evaporation in vacuum. Experimental multi-element SPR device was designed as based on the analysis of TV image obtained for the studied array of calixarene films and tested using saturated ethanol vapors

A biosensor approach to probe the structure and function of the adsorbed proteins: fibrinogen at the gold surface

The kinetics of adsorption and surface structure of adsorbed layers of the human fibrinogen on the gold surface, determined by Surface Plasmon Resonance (SPR) and Atomic Force Microscopy (AFM) analysis, was employed to probe the lateral distribution and preferred orientation of protein molecules within the monolayer. In this study, special sets of immunoassays are presented for fibrinogen adsorption/conformation analysis. The results show that kinetic parameters of antigen-antibody interactions are directly related to the interfacial conformation of fibrinogen molecules. Various interfacial structures of adsorbed fibrinogen aggregates, namely single, bi- and three- molecular aggregates, were obtained using a combination of AFM imaging and SPR analysis. Adsorption of fibrinogen onto the surface of polycrystalline gold is a complex process including surface-induced unfolding, local self-assembly and adsorption, occurring concurrently with – and on the time scale of – each other. This result confirmed the utility of the proposed approach for detecting the spatial distribution and biofunctional properties of specific proteins adsorbed from biological liquids in biosensors.Просторовий розподіл та переважна орієнтація молекул білків у моношарі досліджена з застосуванням кінетики поверхневого плазмонного резонансу (ППР) та мікроскопії атомних сил (МАС) підчас адсорбції фібріногену людини на поверхню золота. У роботі проведена серія специфічних імунних реакцій щоб проаналізувати адсорбційно-конформаційний стан плівок фібріногену. Отримані результати демонструють прямий звўязок кінетичних параметрів реакції антиген-антитіло з конформацією фібріногену на межі розподілу. Застосування МАС і ППР аналізів дало можливість визначити одно-, двух- та трьох молекулярні структурні сполуки фібріногену на межі розподілу. Адсорбція фібріногену на поверхню полікрісталічного золота - це складний процес, що містить: розгортання, стимульоване поверхнею, само-збирання та адсорбцію, які відбуваються конкурентно у часі. Цей результат підтверджує перспективу запропонованого підходу у біосенсорній техніці для визначення просторового розподілу та біофункціональних властивостей специфічних білків, які адсорбуються з біологічних рідин.Пространственное распределение и преимущественная ориентация молекул белков в монослое изучена с использованием кинетики поверхностного плазмонного резонанса (ППР) и микроскопии атомных сил (МАС) при адсорбции фибриногена человека на поверхность золота. В работе проведена серия специфических имунных реакций для адсорбционо-конформационного анализа пленок фибриногена. Полученные результаты демонстрируют прямую связь кинетических параметров реакции антиген-антитело с конформацией фибриногена на границе раздела. Применение МАК и ППР анализов позволило определить одно-, двух и трех-молекулярные сочетания фибриногена на границе раздела. Адсорбция фибриногена на поверхность поликристаллического золота является сложным процессом, включающим, разворачивание, стимулируемое поверхностью, само-сборку и адсорбцию, происходящим конкурентно во времени. Этот результат подтверждает перспективу предлагаемого подхода в биосенсорной технике для определения пространственного распределения и биофункциональных свойств специфических белков, адсорбируемых из биологических жидкостей

The role of shear modulus and viscosity of thin organic films on the adsorption response of QCM sensor

This work reports on the results of numerical calculations of quartz microbalance (QCM) sensors response under adsorption of analyte molecules. The influence of share modulus and viscosity has been studied. It was shown that even in the case of sufficiently thin films (hundreds of nanometers), the viscosity effects can significantly affect the sensor response during adsorption. In the case of sufficiently thick layers, the viscosity effects can turn out to radically change the response of QCM to the adsorption of volatile molecules. Thus, utilizing QCM-based sensors in viscous medium it is necessary to take into account not only mass loaded (adsorbed) onto quartz surface but also effect of viscosity on sensor response

SPR-spectroscopy of protein molecules adsorbed in microwave field

A possibility to use surface plasmon resonance (SPR) in the investigations of the microwave radiation influence upon proteins in the process of their adsorption on the gold surface and their interaction with other proteins. For the first time, this method is applied to experimental study of physical parameters of the biological molecules under the action of the weak (from 1 to 10 mW/ cm²) electromagnetic fields in real-time regime. The changes in the process of adsorption of protein on the gold at different stages of the absorption as well as the changes in the reaction of antigen-antibody were introduced under the action of microwave field. More dense layers of protein was obtained in the microwave fields resulting in the decreased contribution of non-specific and specific interactions between proteins

Dispersion of natural modes in a many-layer planar system

We derive the recurrence dispersion equations for natural modes of a many-layer planar system. As an illustration a five-layer planar system is considered, and solutions for guided-wave polaritons of such a system are found. The behavior and peculiarities of these solutions are analyzed