Improvement of electric pulse shape for electropermeabilization-assisted dielectrophoretic impedance measurement for high sensitive bacteria detection

This paper describes a high sensitive detection method of micro-sized bacteria using a dielectrophoretic impedance measurement method assisted by electropermeabilization with optimized electrical pulse shapes. The authors have previously proposed a bacteria detection technique called DEPIM (dielectrophoretic impedance measurement) method using positive dielectrophoretic force to capture bacteria in suspension onto an interdigitated microelectrode array. Electropermeabilization (EP) has been successfully combined with DEPIM in order to improve DEPIM sensitivity as a result of intracellular ion release through damaged cell membranes. For yeast cells, sensitivity of the electropermeabilization-assisted DEPIM (EPA-DEPIM) was about two orders higher than conventional DEPIM. However, EPA-DEPIM was not so effective for smaller bacteria such as Escherichia coli (E. coli). In the present study, the EP pulse waveshapes were improved, so that conductance increase caused by electrolytic ions release from metal electrodes could be suppressed. This enabled a secure detection of intracellular ions released from bacteria avoiding disturbance of electrolytic contamination from metal ions. Consequently, the lower limit of EPA-DEPIM sensitivity for E. coli detection was improved from 10⁴ to 10² CFU/ml for 3 h diagnosis time.