The persistent microbicidal effect in water exposed to the corona discharge

Area of Science:

• Plasma Physics and Chemistry
• Microbiology
• Water Treatment Technologies

Background:

• Low-temperature plasma (LTP) is known for its direct microbicidal action via short-lived reactive particles.
• A persistent microbicidal effect in plasma-exposed water, mediated by stable compounds, has been observed.
• Understanding the long-term antimicrobial properties of plasma-activated water (PAW) is crucial for its applications.

Purpose of the Study:

• To investigate the persistent microbicidal effect of water exposed to low-temperature plasma.
• To identify the stable reactive species responsible for the long-term antimicrobial activity in PAW.
• To determine the contribution of acidification versus other compounds to the microbicidal action.

Main Methods:

• Exposure of water and phosphate-buffered saline to DC negative glow corona and positive streamer discharge plasma generated in air.
• Analysis of reactive species (NO(x), H(2)O(2), O(3), HCN) using SIFT-MS and measurement of pH.
• Assessment of microbicidal activity against Staphylococcus epidermidis, Escherichia coli, and Candida albicans over a 4-week storage period.

Main Results:

• Plasma exposure generated NO(x), acids, H(2)O(2), and O(3) in water and PBS.
• The microbicidal effect persisted for 4 weeks, with significant inactivation of bacteria and fungi.
• Acidification was identified as the primary microbicidal factor, although other unidentified compounds may contribute.

Conclusions:

• Low-temperature plasma-activated water exhibits a stable, long-lasting microbicidal effect.
• Acidification of the water is the main driver of this persistent antimicrobial activity.
• While reactive oxygen species diminish, the acidic environment effectively inactivates microorganisms.