Тhe search for new materials with high conductivity and biocompatibility for use in biosensors is an important task. One promising material is bacterial cellulose (BC) due to its high surface area, high porosity, and biocompatibility. In this study, bacterial cellulose is modified with the PEDOT:PSS conductive gel and carbon nanomaterials to increase conductivity. Thermally expanded graphite/BC/PEDOT:PSS/graphene composition is used to immobilize Gluconobacter oxydans acetic-acid bacteria on the surface of a screen-printed carbon electrode. The effect of individual components of the composite on the catalytic activity of bacteria in the presence of 2,6-dichlorophenolindophenol redox mediator is studied. The addition of BC to the composition provides a higher stability of the electrode: the drop in signal within 35 days is 9%. A microbial biosensor based on TEG/PEDOT:PSS/Graphene/BC/ G. oxydans composite show better sensitivity (36.4 µA mM –1 cm –2 ) and lower detection limit (0.005 mM) as well as the widest linear detection range (0.005–2 mM) compared to the other compositions. Thus, bacterial cellulose modified with conductive additives can be applied as a matrix for the immobilization of bacteria in microbial biosensors and microbial fuel cells.

The work considered the properties of a biosensor based on a novel nanomaterial-modified thermally expanded graphite (TEGM). The main focus was on whether the procedure of additional graphite thermal expansion would affect the electrochemical properties of biosensors based on membrane fractions of acetic acid bacteria Gluconobacter oxydans. Raman spectroscopy, scanning electron microscopy and electrochemical analysis were used for the study. Raman spectra showed that the formation of TEGM led to its stratification into smaller particles and a better orderly layered structure with high "graphenization" degree. Modification of TEG led to the formation of additional cavities into which bacterial cells or bacterial membrane fractions could be immobilized and affect the electrical conductivity of the biosensors positively. Calculation of the heterogeneous charge transfer constants showed that processes occurring on the electrodes are quasi-reversible. The limiting stage of these processes is the transfer of an electron from a biological component on the electrode surface, not the diffusion of the analyte from the solution to the active centers of the enzyme. We showed the possibility of developing third-generation mediator-free biosensors for glucose detection based on TEGM, as well as of second-generation mediator biosensors for glucose, ethanol and glycerol detection.

Bacterial cellulose (BC) produced by the Komagateibacter sucrofermentas VKPM B-11267 bacteria was used as a carrier for immobilization of acetic acid bacteria Gluconobacter oxydans in amperometric biosensors. The bioreceptor was formed on the surface of a screen-printed graphite electrode modified with thermally expanded graphite (TEG) or on the surface of a porous three-dimensional material, nickel foam (NF). Structural features of these materials contributed to the creation of a firm contact between the electrode material and the surface of the BC on which the bacterial cells were immobilized. Scanning electron microscopy showed that bacteria not only sorb on the surface of BC but are also able to penetrate the inner volume of the film. Conductivity of both types of biosensors was studied using impedance spectroscopy and the resistance of the graphite electrode was shown to decrease by three orders of magnitude after its surface is modified with TEG. Bioelectrodes containing BC were used in the construction of an amperometric biosensor for glucose determination. The sensitivity of the biosensor was 3 μA/mM × cm2. Thus, BC in combination with TEG and NF can be used to create three-dimensional electrodes of bioelectrocatalytical devices.

Recent years have witnessed an ever-increasing interest in developing electrochemical biosensors based on direct electron transfer-type bioelectrocatalysis. This work investigates the bioelectrocatalytic oxidation of glucose by membrane fractions of Gluconobacter oxydans cells on screen-printed electrodes modified with thermally expanded graphite and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Electrooxidation of glucose was shown to occur without the presence of electron transport mediators. Chronoamperometric and cyclic voltametric characteristics showed an increase of anodic currents at electrode potentials of 0–500 mV relative to the reference electrode (Ag/AgCl). The direct electron transfer effect was observed for non-modified PEDOT:PSS as well as for PEDOT:PSS linked with crosslinkers and conductive fillers such as polyethylene glycol diglycidyl or dimethyl sulfoxide. Bioelectrodes with this composite can be successfully used in fast reagent-free glucose biosensors.

This review deals with the use of the highly conductive polymer PEDOT:PSS in biomedical and bioelectrochemical systems. The examples of toxic effects on living cells, positive effects of PEDOT:PSS on the viability of cells and tissues are given. The properties of the polymer, methods of increasing its electrical conductivity by its modification with various nanoparticles and nanomaterials are discussed. Examples of using PEDOT and its composites in bioelectrochemical devices, such as biosensors and biofuel cells, are considered. Changes in the characteristics of biosensors and biofuel cells under the influence of PEDOT are discussed.

Microbial biofuel cell (BFC) was used as a primary energy source for energy storage system. The converter BQ25504 (Texas Instruments) was applied for transformation of electrical energy from microwatt primary sources. The energy storage operation begins if BFC output voltage was higher or equal to 300 mV. In case of stationary operation it was possible to provide energy storage of BFC output voltage equal to 100 mV. The developed system based on converter enables to increase the initial voltage BFC of 0.5 V to 3.1 V; accumulated energy is stored on the various capacitors. Resulting voltage was stable with application of condensers with capacities from 100 mu F to 6800 mu F. In case of application of 3.1 V and 6800 mu F condenser the storage energy was equal to 32.7 mJ. It was enough to provide short time operation of diode L-1154SURDK (2.0 V, 20 mA) and electrical motor M25E-4L (MITSUMI; 3.0 V, 100 mA). Designed system can be applied for energy supply of small electrical devices (for example remote sensors) and autonomous microrobots.

We studied bioelectrocatalytic oxidation of ethanol with membrane fractions of Gluconobacter oxydans VKM B-1280 bacterial cells participating as an electrocatalyst. Material of the electrode was graphene-like thermally expanded graphite of a high surface area and low resistivity. Membrane fractions were immobilized on the electrode surface by application in chitosan gel to prevent desorption of the biocatalyst. The bioelectrode characteristics were studied by the voltammetric and chronopotentiometric methods. It was shown that electrooxidation of ethanol on the bioanode could proceed both in the mode of direct mediator-free electrocatalysis and by the mediator mechanism.

Contents 1. IntroduCtIon (187) 2. Modern developMent dIreCtIons for BfC (190) 3. developMent of the BIoanode of a fuel eleMent on the BasIs of therMoexpanded graphIte (191) 3.1.Development and production of the bianode model (193) 3.2.Electrophysical researches (194) 4. applICatIon of a graphene In BIofuel eleMents (197) 4.1.The application of graphene materials for BFC electrodes (200) 5. ConClusIon (204) referenCes (204) NANOSYSTEMS

The present paper concerns the activity of the microbic biofuel element which oxidizes ethanol. The intact bacterial cells of Gluconobacter oxydans or their membrane fractions were used as a bioelectrocatalyst. Thermoexpanded graphite (TEG) was used as a material of an electrode. The used strain of bacterial cells, as well as carbon composition types will make a basis of a prototype of a microbic biofuel element at development of the block of transformation and accumulation of electric energy.

Reshetilov AN, Kitova AE, Arkhipova AV, Kratasyuk VA, Rai MK. 2012. Determination of ethanol in acetic acid containing samples by a biosensor based on immobilized Gluconobacter cells. Nusantara Bioscience 4: 97-100. A biosensor based on Gluconobacter oxydans VKM B-1280 bacteria was used for detection of ethanol in the presence of acetic acid. It was assumed that this assay could be useful for controlling acetic acid production from ethanol and determining the final stage of the fermentation process. Measurements were made using a Clark electrode-based amperometric biosensor. The effect of pH of the medium on the sensor signal and the analytical parameters of the sensor (detection range, sensitivity) were investigated. The residual content of ethanol in acetic acid samples was analyzed. The results of the study are important for monitoring the acetic acid production process, as they represent a method of tracking its stages.

Seven microbial strains were screened for their ability to detect disaccharides as components of Clark-type oxygen biosensors. Sensors responded to varying degrees to maltose, cellobiose, sucrose, and melibiose, but none responded strongly to lactose. Although microbial sensors are relatively nonspecific, it is possible to obtain differential measurements of specific substrates using multiple sensors with different relative specificities. For example, Escherichia coli strain K-802 oxidized maltose but had low activity against sucrose, while Bacillus subtilis strain VKM B-434 responded more strongly to sucrose than maltose. Furthermore, signals from these two sensors were additive for selected samples. Results suggest that a two-component biosensor utilizing these strains could be used for differential detection of sucrose and maltose.

NMR spectroscopy was applied for studying the products of glucose and sorbitol oxidation by cells of Gluconobacter oxydans. An analysis of 1H NMR spectra showed that the transformation of glucose results in the formation of diketogluconic acid, and sorbitol is oxidized to sorbose. In the 32P NMR spectra, only a signal of inorganic phosphate was detected, which accumulated in the medium as a result of cell lysis.

The parameters of sensors on the basis of glucose oxidase and alcohol oxidase for glucose and ethanol detection have been studied. A combination of glucose oxidase sensor and commercial glucoamylase preparation, Alcoholase II 400, was used for starch detection. Sensors were used to detect glucose in some vegetables and fruits, to measure starch content in some groats, and to detect glucose and ethanol in model fermentation medium.

A method is proposed for determination of starch content in samples using a biosensor based on glucose oxidase and the commercial preparation Alcoholase II 400 containing highly active glucoamylase as the main component. Alcoholase was used in the immobilized form and as solution as well. In both cases, analysis of the sample did not exceed 5-10 min. The method was used to measure starch content in some vegetables, fruit, flour samples, and a model fermentation medium.