Enhancement of Copper Antiviral Activity with Glutathione Treatment

Copper and its alloys have antimicrobial activity effective for various pathogens. Their application to touch surfaces successfully reduced bioburden in hospital intensive care units but failed to completely prevent the transmission of pathogens derived from the hospital room. Discoloration of pure copper with surface oxide growth is another issue to discourage its application to touch surfaces. Common copper alloys have relatively high resistance to discoloration, but their antimicrobial activity is lower than that of pure copper. Therefore, enhancement of the antimicrobial activity of copper alloys is beneficial for their touch surface application. In this study, glutathione was employed for surface treatment of copper and its alloys to enhance their antiviral activity. Treatment with 4 mM glutathione in 99 vol % ethanol-1% H₂O markedly enhanced copper and its alloys' antiviral activities against bacteriophage Qβ except MONEL, which has the lowest Cu content (33.4 wt %). Electrochemical impedance measurement under a thin electrolyte film revealed acceleration of copper and its alloys' corrosion by the glutathione treatment. The antiviral activity of tested materials with the glutathione treatment correlated well with their corrosion rate, except MONEL. Potentiodynamic and chronopotentiometry measurements in 6 M KOH + 1 M LiOH demonstrated reduction in the thickness of the surface oxide layer by the glutathione treatment. These facts suggest that the glutathione treatment reduces the surface oxide layer, resulting in acceleration of corrosion with an increase in Cu ion release, which enhances antiviral activity.