Non-thermal atmospheric pressure plasma jet for the bacterial inactivation in an aqueous medium.

This study reports the potential of non-thermal atmospheric pressure plasma jet for the bacterial inactivation in an aqueous medium. All experiments were conducted in a reactor containing aqueous solution i.e., water, pre-inoculated with bacterial suspensions and after plasma exposure solution is inoculated in Petrifilm to know the viable count. The plasma jet exposure to the bacterial aqueous solution was carried out under various gases such as helium, argon, air and also in combination as Argon + Air and Helium + Air. In each case, the oxidizing species such as hydrogen peroxide, nitric acid, hydroxyl radicals and ozone formed in the reactor during the plasma exposure were quantified. The effect of applied voltage and gas flow rate were studied to optimize the conditions for its efficacy. The solution pH plays a prominent role in bacterial inactivation, as the process is effective at low pH exhibiting 7 log reduction of bacterial population. The bacterial inactivation is efficient at below the critical pH (<4.7) and the inactivation process becomes less effective if the pH goes above 4.7. Plasma treatment of deionized water produces some reactive species such as hydrogen peroxide and nitrates, this plasma treated water is used to test the bacterial inactivation. Addition of Fe salt to the plasma treated water improves the efficacy by converting hydrogen peroxide to hydroxyl radicals, which serves to be a major contributor to the bacterial inactivation. Especially, Non-thermal plasma offers an alternative way to sterilize vacuum sensitive and thermo-labile living tissues.