In-situ disinfection by flexible surface dielectric barrier discharge plasma film: discharge modes and mechanisms

In this work, a surface-dielectric-barrier-discharge (SDBD) based flexible plasma film (FPF) was established and tested for in-situ surface disinfection. The discharge product mode (i.e. O₃ mode and NO_x mode) was controlled by the applied voltage and verified by in situ gas product quantification. For in situ disinfection, the NO_x mode shows significantly higher bactericidal efficiency than the O₃ mode, and the FPF achieves ∼3.5 logs and >6 logs of bacterial reduction with 3 and 5 min of plasma exposure in the NO_x mode, respectively. The underlying mechanism is investigated. In the O₃ mode, the heating effect of the plasma plays either a negligible or moderate role in bacterial inactivation, depending on the applied voltage. In the NO_x mode, both high temperature and long-lived species can play a role, while it is speculated that short-lived species are primarily responsible for the high-order bactericidal rate (>3 logs), with atomic oxygen likely playing an important role. As revealed by scanning electron microscopy and Fourier-transform infrared (FT-IR) spectroscopy, the NO_x mode can lead to more pronounced bacterial etching and nitrification compared to the O₃ mode, accounting for its superior disinfection performance. By examining the time-dependent FT-IR infrared spectra of treated bacteria, it is found that nitrification is the dominant spectral variation, and the ratio of infrared bands at 1354 and 1654 cm⁻¹ can serve as a positive indicator of disinfection efficiency. This study can provide deeper insights into the discharge mode, disinfection performance, and bactericidal mechanisms of the SDBD-based FPF, offering guidance for the control, evaluation, and future applications of this technology.