The direct and indirect bactericidal effects of dielectric barrier discharge (DBD) cold atmospheric-pressure microplasma in an air and plasma jet generated in an argon-oxygen gas mixture was investigated on Staphylococcus aureus and Cutibacterium acnes. An AC power supply was used to generate plasma at relatively low discharge voltages (0.9-2.4 kV) and frequency (27-30 kHz). Cultured bacteria were cultivated at a serial dilution of 10-5, then exposed to direct microplasma treatment and indirect treatment through plasma-activated water (PAW). The obtained results revealed that these methods of bacterial inactivation showed a 2 and 1 log reduction in the number of survived CFU/mL with direct treatment being the most effective means of treatment at just 3 min using air. UV-Vis spectroscopy confirmed that an increase in treatment time at 1.2% O2, 98.8% Ar caused a decrease in O2 concentration in the water as well as a decrease in absorbance of the peaks at 210 nm, which are attributed NO2- and NO3- concentration in the water, termed denitratification and denitritification in the treated water, respectively.
Keywords: DBD microplasma; UV-Vis spectroscopy; nitrogen species; plasma activated water; plasma jet; reactive oxygen; sterilization.