Evaluation methods for bacterial inactivation and impairment by nanowire-assisted electroporation

Abstract

As compared with the conventional electroporation by using plate electrodes with voltages of thousands of volts, nanowire-assisted electroporation (NW-EP) under low-voltage supply has been well demonstrated to be a green and efficient disinfection method via the formation of locally enhanced electric field near nanowire tips. These finite strong electric fields inactivated bacterial cells by inducing unrecoverable damages on rigid cell wall, and creating reversible and irreversible pores on flexible membrane. However, due to their random exposure by nonuniform and nanosized strong electric field over nanowire tips, both reversible and irreversible membrane pores on bacterial cells were formed during NW-EP disinfection. Herein, we employed a membrane-impermeable propidium iodide (PI) dye to stain NW-EP influent and effluent for distinguishing cell damages with PI-detectable reversible and irreversible membrane pores. Meanwhile, considering the inaccessible reversible membrane pores with sizes smaller than PI molecules, selective plates with NaCl addition were prepared to induce high osmotic pressure for inhibiting the growth and reproduction of bacterial cells with damaged cell wall and intact cell membrane, namely reversible membrane damages. These methods well revealed the mechanisms of cell inactivation and impairment by NW-EP. It can provide fundamental information for designing synergistic strategy of NW-EP with other oxidizing disinfectants, which potentially enhance disinfection performance via promoting the oxidant diffusion into cells for inactivation of bacterial cells and elimination of intracellular hazardous substrates.