Electrochemical Removal of Bacteria from Zinc Oxide Nanopillars Synthesized on Stainless Steel

Nanopillars are high aspect ratio nanoscale surface topographies that can serve a variety of applications. In many of these applications, nanopillars may come into direct contact with bacteria. Accumulation of bacterial biofouling may render the nanopillars ineffective. If nanopillar surfaces are intended to be reused, methods to remove bacterial debris or biofouling from the nanopillars are required. In this proof-of-concept study, we investigated an electrochemical treatment to remove biofouling from a model nanopillar surface: zinc oxide nanopillars synthesized on stainless steel (ZnOSS). We exposed ZnOSS coupons to Bacillus subtilis, Staphylococcus aureus, Escherichia coli, or Pseudomonas aeruginosa under various biofouling scenarios. Next, we subjected each coupon to an electrochemical treatment wherein the ZnOSS coupon acted as the working electrode. We found effectiveness of the electrochemical treatment was specific to the biofouling scenario and specific to the bacterial species. The treatment was effective at removing microcolonies of all species from ZnOSS in as little as 30 s, but it was completely ineffective against a concentrated accumulation of S. aureus biofouling such as that deposited from the coffee ring effect. The mechanism of biofouling removal during the treatment could be attributed to a combination of bubbles produced at the surface, which lifted off attached bacteria, as well as the presence of antibacterial oxidants generated during electrolysis. Overall, our findings suggest that the proposed electrochemical treatment would be ill-suited to restore zinc oxide nanopillars that are heavily contaminated but could be compatible for applications in which nanopillars are cleaned after exposure to low concentrations of bacteria.