Activity of microorganisms depends on several factors, among them — the quality of water, various emissions, strains of microorganisms, deviations in metabolic processes, etc. Favorable conditions stimulate activities, whereas pathogenic conditions inhibit them. A significant advantage of microorganisms as a biosensor is a high sensitivity, detection of nonspecific stimulants/pathogens that exert a complex effect on metabolism, low cost and rapidity of tests. To measure the activity of microorganisms, the ethanol fermentation of ‘Baker’s yeast’ (Saccharomyces cerevisiae) is used, where a glucose is converted into ethanol and carbon dioxide. The amount of produced CO2 depends on the yeast activity, which in turn is detected as a varyation ionic content in the reagent containers. The recognition of nonspecific stimulation/pathogenicity is based on accurate electrochemical measurements by comparing control and experimental populations.

Description of the device. The device represents a differential EIS measuring system with 100ml containers. Since the fermentation depends on temperature, the reagent chambers have a built-in thermostat, which maintains a constant temperature. Alcohol fermentation is carried out in conventional containenrs with temperature sensors. To prevent the effect of biophotonic transfer between populations, all containers are separated from each other. The device is connected to the MU3.4 measurement module that it communicate with PC via USB interface. Graphs are plotted automatically. One measurement lasts about 120-180 minutes; only yeast, sugar, water and the measuring device are needed for the test.

Bio-hybrid systems research. This system is an interfacing tool for electrochemical handling of microorganisms (yeast or algae) on a population level, exploring feedback mechanisms, controlling metabolic activities, analysing sensing and actuating capability of microorganisms. It provides biopotential, electrochemical, thermal and optical interfaces to fluidic solutions of yeast/algae (or other microorganisms). There are several versions of this device, also for bioreactors, with increased number of electrodes for better intractability with populations.