Наука России: Цели и задачи -5 -РАЗДЕЛ I. ФИЗИКА Гуторов М.А

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.

The effect of carbon nanomaterials (carbon nanotubes, thermally expanded and pyrolytic graphite) on the bioelectrochemical activity of Gluconobacter oxydans bacterial cells was studied during sorption contact with nanomaterials. For bacterial immobilization, the surface of a working bioelectrode was modified via the application of bacterial suspension in the studied nanomaterial and chitosan. The bioelectrochemical electrode characteristics (the amplitude of generated potential, cyclic volt–ampere characteristics, resistance) were estimated before and in the process of bacterial interaction with ethanol (3-electrode measurement scheme). Modification of the spectral graphite electrode by carbon nanotubes allowed a decrease in the resistance of the charge transfer by 48% and an increase in the oxidation current on cyclic volt—ampere characteristics at a voltage of 200 mV by 21% as compared with nonmodified electrode. The thermally expanded and pyrolytic graphite increased the bioelectrode resistance to 4050 and 8447 Ohm cm2, respectively. Mathematical modeling demonstrated that from 75 to 100% of biomaterial (depending on the used nanomaterial) were involved in the process of electricity generation with the selected method of the bacterial immobilization. The use of data obtained during the development of microbial biosensors and electrodes of biofuel cells is discussed.

We have studied the properties of a bioelectrode formed by the immobilization of Gluconobacter oxydans bacterial cells on carbon superfine materials (CSMs). We use three types of CSMs (as adopted by the working classification CSM 1–3) with different carbonization rates. The bioelectrode is formed by covering the surface of the CSM suspension of bacteria in a chitosan gel. The properties of samples are evaluated by measuring the physiological state of the bacteria immobilized: (a) recording the intensity of cellular respiration, (b) for measuring the charge transport characteristics of electrode (bioelectrocatalysis), and (c) by measuring the electrode impedance. Measurements (b) and (c) are made on two and three-electrode circuits in the oxidation of ethanol in the presence of 2,6-dichlorophenol bacteria electron transport mediator. For CSMs 1 and 2 the electron transport by the oxidation of the substrate is not registered, while for CSM 3 the current generation occurs. The resistance of CSM 3 bioelectrode is below the resistance of CSMs 1 and 2 both before (39.6 kΩ/cm 2 for CSM 3, 630 Ω/cm 2 for CSM 2, and 1329 Ω/cm 2 for CSM 1) and after the addition of the substrate (2.9 kΩ/cm 2 for CSM 3, 45 kΩ/cm 2 for CSM 2, and 58 kΩ/cm 2 for CSM 1). The bioelectrode made of CSM 3 has a capacitance of 196 μF/cm 2 —greater than two orders of magnitude of the bioelectrode capacity of CSMs 1 and 2 (0.51 and 0.58 μF/cm 2 , respectively). It is important to further study the properties of the CSM class of materials, which are promising as the basis of mechanically flexible electrodes with controlled parameters.

The process of template-free DNA synthesis was detected in two ways: by measuring the pH of the solution by a semiconductor sensor and by measuring the conductivity in the recording of impedance spectra. Synthesis was carried out without using template DNA, with only two enzymes being involved in the reaction: DNA polymerase and nicking endonuclease (nickase) in the presence of deoxynucleotide triphosphates. Previously, Purushothaman et al., by applying the recording of the results of template-directed synthesis with a pH-sensitive field-effect transistor, showed that protons are released into solution in the incorporation of nucleotides [4]. Regarding this, it was important to establish that the same release of protons into solution occurred in the template-free synthesis as in the template-directed synthesis and to identify the changes by measuring the conductivity of the solution using impedance spectra. It was found that the template-free synthesis was accompanied by the generation of protons (ΔpH is ~1.5 pH at an initial concentration of deoxynucleotide triphosphates of 150 µM) and a decrease in the value of active impedance component by ~25% of the initial value. The effect of a decrease in the active impedance component was explained as being due to an increasing conductivity of medium due to a growth in the concentration of protons.