Yu.M. Shirshov

Ammonia sensors based on sensitive polyaniline films

Abstract We propose a new type of ammonia sensor with polyaniline (electroconducting polymer) as the sensitive element. Such sensors are characterized by high sensitivity, wide range of measured concentrations (1–2000 ppm) and high stability of electrical parameters. The use of polyaniline ensures high chemical stability of the sensors in oxidizing ambients. A sensor design based on a silicon chip custom-packed into a linear plastic case is presented. The chip is provided with a system of heaters and thermometers to check the temperature regime of sensor operation. We have studied I – V curves, temperature, concentration and kinetic characteristics of the sensors, as well as their ageing. The possibility for thermoregeneration of the sensor parameters after long-term functioning in an ammonia ambient is emphasized.

Multienzyme electrochemical sensor array for determination of heavy metal ions

Abstract A multienzyme electrochemical sensor array is developed. It is based on capacitance pH-sensitive electrolyte–insulator–semiconductor (EIS) sensors with silicon nitride ion-sensitive layers and different forms of cholinesterase, urease and glucose oxidase as sensitive elements. With this sensor array, we used a multienzyme analysis to recognize the heavy metal ions in solutions containing a mixture of different metal ions, as well as for determination of their content in the analysed samples. The content of toxic elements was determined by estimation of the residual activity of enzymatic membranes after the injection of analysed samples. The conditions for enzyme sensors operation, such as buffer capacity, substrate concentration, time of incubation and time of response signal measurement, were optimised to reach the maximal sensitivity of multisensor for analysis of heavy metal ions in the investigated solutions. It was shown that multienzyme analysis followed by mathematical processing is an efficient approach to develop sensor arrays for toxic substrates detection.

Surface plasmon resonance sensor for pesticide detection

Abstract The optoelectronic biosensor, based on surface plasmon resonance (SPR) for detection of photosynthesis-inhibiting pesticides in aqueous solutions was presented. The pesticide capability to replace plastoquinone from its complex with D1 protein was used for the detection. This replacement reaction results in the changes of the optical characteristics of protein layer, immobilized on the gold surface. Monitoring of these changes with SPR-technique permits to determine 0.05–5.0 μg/ml pesticide in solution within 1 h.

Surface plasmon resonance spectroscopy: prospects of superstrate refractive index variation for separate extraction of molecular layer parameters

Abstract A computational procedure for separate determination of n and d of thin transparent layers using the surface plasmon resonance (SPR) spectroscopy with variation of the refractive index of the solution and its application to immunic reaction studies are presented. This procedure is essentially based on a direct fitting of a set of the resonant curves. Effect of the experimental conditions and measurement errors on the accuracy of the data obtained has been analyzed. Precise measurement of the angle of incidence and the refractive index of the solution were found to be important for the correct determination of the layer parameters. This technique was applied to a mouse IgG and an anti-mouse IgG interaction study. It has been demonstrated that n and d of the molecular layer can be determined with reasonable accuracy even using relatively small variation of the refractive index of the solution.

A sensor based on the planar-polarization interferometer

Abstract We have successfully used a single-beam planar interferometer based on the silicon-silicon dioxide-silicon nitride-phosphosilicate glass multilayer structure, s -and p -polarizations of the same light beam are used as its individual arms. The high sensitivity of the device when serving as a refractometer and an immunosensor is demonstrated. The experimental results are shown to be in a good agreement with those calculated within the framework of a transverse synchronism.

Optical parameters of thin calixarene films and their response to benzene, toluene and chloroform adsorption

Abstract Ellipsometry and surface plasmon-polariton resonance were used to measure both the thickness, d, and refractive index, N, of tert-butylcalix[n]arene (n = 4, 6 and 8) films, as well as the effect of the adsorption of benzene, toluene and chloroform on these parameters. The refractive index values were found to lie in the range 1.56–1.58. Exposure to benzene (chloroform) vapour increased N by 0.01–0.02, while toluene adsorption led to calixarene film swelling (up to 10–12%). Warming the films in air at 160 °C restored the former values of both d and N. Some mechanisms of interaction between the adsorbate molecules and calixarene films are proposed.

Self-assembled multilayer superstructures as immobilization support for bioreceptors

A new strategy for the preparation of layer-by-layer inorganic assemblies are discussed which allows simple fabrication of multifunctional thin film on various substrates. The procedure involves alternating layers of the cyanoferrate derivatives with layers of copper ions. A film growth was investigated in situ by surface plasmon resonance (SPR) and characterized by atomic force microscopy (AFM). It was shown that the topography of the surface strongly depends on a number of layers. In particular, the change-over to the formation of 3D aggregates after 12–15 cycles of deposition was observed. It was demonstrated that biological captors, immunoglobulins, can easily be immobilized onto these films in closely packed oriented monolayer, and stable theoretically predicted response was obtained in SPR geometry. This suggests that the functional multilayer built using this approach will have useful application owing to their controllable chemical reactivity.

Calixarene-coated nanoparticle gold films for chemical recognition system

Nanoparticle metal films functionalized with calixarenes offer a novel technology for highly effective, technologically feasible, small and cheap chemical gas sensors. We have designed, manufactured and measured the performance of chemical gas sensor elements, where molecular absorption by the calixarene layer controls the electrical conductivity of a nanoparticle gold film evaporated on a dielectric substrate. The sensors were exposed to several alcohol and water vapors and the dynamic sensor responses were analyzed. Resistance variation of the measured samples achieves 10%. Current-voltage curves, recovery characteristics and temperature dependencies of the sensor elements were investigated. Degradation of the sensitivity due to the aging effect was observed. We show that differences in the sensor recovery time, as well as concavity or convexity of the leading edge of the sensor transition curve could be used as additional information parameters for chemical recognition system.

Light scattering by molecular-organized films on the surface of polycrystalline gold

Specific features of the structure of self-assembled layers of dodecanthiol on the surface of polycrystalline films of gold are investigated with the aim of revealing the effect of the substrate relief on the lateral distribution and the predominant orientation of thiol molecules within the limits of the layer. The analysis of the angular dependence of quasi-elastically scattered light that takes into account the contributions of the geometric roughness of the surface and the inhomogeneity of the dielectric constant to scattering allowed us to establish the correlation in antiphase between the distribution of the thickness of the thiol coating and the height of the relief of the gold surface. The formation of a thiol layer on the surface of polycrystalline gold is a complex process including adsorption, local self-assembly, and a surface-induced distortion of the ordered structure in the regions of minima of the surface relief. The approach proposed here and based on the nondestructive analysis of thin organized coatings can be efficiently applied for the study of specific features of the topography and the prediction of chemical functionality of self-assembled molecular ensembles.

Computer simulation of transport processes in biosensor microreactors

Abstract Microelectronic ferment reactors are finding increasing employment as base elements of biosensor matrices. In this work, a computer simulation of a microelectronic reactor based on ion-sensitive elements, such as transistor or electrolyte—insulator—semiconductor structure, is presented. Our objective involved elucidation of quantitative relations between the sensor design and its characteristics. The computer simulation is performed for different versions of both enzyme carriers and their positions in the microreactor cell. The results of simulation enabled us to optimise both design and all-over dimensions of the microreactor. The principal sensor parameters (such as response rate, amplitude and time lag) are calculated for the optimum cell. A comparison between the calculated models and the corresponding experimental results obtained with the help of considered types of microreactors is carried out.