Pretreatment of cell membranes for improved electropermeabilization-assisted dielectrophoretic impedance measurement

We improved our previously reported highly sensitive bacteria detection method called electropermeabilization-assisted dielectrophoretic impedance measurement (EPA-DEPIM), which counts the number of bacteria by measuring changes in impedance. EPA-DEPIM involves two processes: collection of bacteria by dielectrophoresis (DEP), followed by electropermeabilization (EP) of the cell membranes. In DEP, bacterial cells in aqueous solution are collected on microelectrodes by the dielectrophoretic force. In EP, a pulse-like rectangular wave is applied to the collected cells to disrupt their membranes. This increases the signal sensitivity because the disrupted membranes release intracellular ions that increase the change in impedance. However, the pulse-like EP wave creates a strong electric field that causes metal ions to be released from the microelectrodes, increasing the blank signal to levels comparable to that for a low-concentration Escherichia coli suspension (102 cells/ml). To address this problem, we demonstrated the efficacy of two types of pretreatment applied before the EP wave: chemical pretreatment by exposure to hydrogen peroxide, and physical pretreatment by a small pulse-like voltage. Both pretreatments successfully intensified the change in impedance even at a lower EP voltage.