Action of an Argon/Water Vapor Plasma Jet in the Sterilization of Silicone Contaminated with Candida albicans

Abstract

This work evaluates the influence of argon/water vapor plasma jet exposure time on surface sterilization of a silicone substrate contaminated with Candida albicans. For this purpose, gliding arc-type geometry was used to generate a nonthermal plasma jet at an applied power on the order of 20 W under water vapor carried by an argon flow of 5 L/min. C. albicans biofilms were grown on silicone plates with a 2cm2 area. Samples were treated with a plasmajet for different exposure times, resulting in the following sample groups: nontreated (A) or treated with plasma for 2 min (B), 5 min (C), 10 min (D), and 20 min (E). Experiments were performed in triplicate. To evaluate the action of the plasma jet on the contaminated samples, colony-forming units (CFUs) were counted before and after plasma exposure. Scanning electron microscopy (SEM) was used to analyze the morphological modification of the treated substrate, whereas Fourier transform infrared spectroscopy (FT-IR) was used to analyze the bare substrate after exposure to plasma. Optical emission spectroscopy was used to investigate the plasma species in the ultraviolet range. Results indicated reductions in CFUs of 42.4%, 74.2%, 83.7%, and 97.5% for groups B, C, D, and E, respectively. SEM images showed that groups D and E suffered more external cellular changes with shriveled, swollen, and/or deformed aspects. These effects can be attributed to reactive species in the plasma such as hydroxyl radicals (OH), which were increased considerably with the presence of water vapor in the mixture with argon gas. A quality change in the surface of the silicone material after 20 min of plasma treatment was observed with the results of the SEM and FT-IR analyses. Finally, the argon/water plasma jet promoted only a slight increase in substrate temperature (up to 310 K) for the investigated conditions, which is very convenient for thermal-sensitive material sterilization.