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We have studied immobilization of Paracoccus yeei VKM B-3302 cells in an organosilica sol–gel matrix consisting of tetraethoxysilane, methyltriethoxysilane and polyvinyl alcohol as a structure-modifying agent. Optical microscopy showed that higher amounts of methyltriethoxysilane make the solid material structure softer. In addition, formation of structures, probably, with bacterial cells inside was spotted. We have analyzed the catalytic power of the immobilized bacteria and discovered that the material’s catalytic potential is the highest at 50% of methyltriethoxysilane. Therefore, this seems to be the best ratio of precursors in a material for bacteria to become effectively encapsulated. Analysis of the material structure by low-temperature nitrogen absorption and scanning electron microscopy revealed that in the given conditions the material got crack-like mesopores and spherical particles of about 25 µm in diameter with immobilized bacterial cells on their surface. The study found that the fabricated organosilica material can effectively protect bacterial cells against UV radiation, pH change, high salinity and high heavy metal ion concentration.

This work proposes a method of forming a microorganism–mediator(s) receptor system, in which the rates of separate stages of mediator bioelectrocatalysis are used as the basis for the development of biosensors for the biochemical oxygen demand (BOD) rapid assay. In the presence of a ferrocene mediator, the yeast Blastobotrys adeninivorans was shown to enable oxidation of a larger range of substrates as compared with other investigated microorganisms—bacteria Escherichia coli and yeast Ogataea polymorpha. The rate constants of the interaction of the yeast B. adeninivorans with nine compounds, electron transfer mediators, were determined; the best mediator for these microorganisms was found to be neutral red (k(int) = 0.681 ± 0.009 dm(3)/g s). Neutral red possesses a high rate of interaction with the ferrocene mediator (14,200 ± 100 dm(3)/mol s) shown earlier to be the most promising acceptor of electrons at a carbon paste electrode (0.4 ± 0.1 cm/s). These features enabled the formation of a two-mediator ferrocene–neutral red system to be used in a biosensor. A two-mediator-based biosensor had a higher sensitivity (the lower limit of detected BOD concentrations, 0.16 mg/dm(3)) than that of a one-mediator system based on neutral red and ferrocene. Analysis of ten samples from surface water reservoirs showed the combination of ferrocene, neutral red and the yeast B. adeninivorans to enable the data that highly correlated (R = 0.9693) with those of the standard method.

This research shows that high-performance biosensors can be produced by modification of screen-printed electrodes with enzymes and conducting hydrogel based on sol–gel matrix and single-walled carbon nanotubes. Tetraethoxysilane, dimethyldiethoxysilane and polyvinyl alcohol were used as the sol–gel matrix basis. Modified SWCNT provide direct electron transfer during glucose oxidation, as confirmed by cyclic voltammetry. The developed conducting sol–gel screen-printed electrodes can determine glucose within the concentration range 0.045–1.04 mM. The developed biosensor is not only in pace with its world analogues but even exceeds them by some analytical and metrological properties. The developed conducting sol–gel biosensor was used to measure the concentration of glucose in blood. The test results differed only insignificantly from those received with the help of standard glucose meter.