A better understanding of the biological functions of microorganisms is required to reduce their threats and increase their usefulness. Therefore, the importance of real-time evaluation of bacterial activity increase for various purposes such as hygiene management, development of antibacterial agents, and effective utilization of bacterial resources. This necessitates a quantitative assessment of metabolic processes, including growth and respiration. Here we would like to introduce the development of electrochemical methods for assessing bacterial activity. 
Electrochemical detection of viable bacterial cells was performed using a cell membrane permeable electron mediator and redox-active pigment. A tetrazolium salt was converted to an insoluble reduction form through the respiration of microbial cells. The insolubility of this formazan was effectively exploited as a surface-confined oxidation event. The electrochemical oxidation of formazan was effectively coupled with the thermal lysis of microbes. The sensitivity of the present technique is up to 10,000-fold higher than that of colorimetry and requires an incubation time of only 1 h. Furthermore, the measurement of the reduction current of tetrazolium salt provides an effective means for assessing the bacterial activity in suspension.