Antibacterial efficacy of surface aluminum oxide nanostructures produced by hot water treatment

Abstract

This study utilizes a hot water treatment (HWT) method for introducing antibacterial properties to aluminum (Al) surfaces, which has relevance in several industries ranging from food packaging and ventilation systems to biomedical materials. The HWT process can produce a nanostructured oxide layer on a wide range of metallic materials by simply immersing the metal in water at temperatures ranging from 75°C to 95°C. In this work, Al foil was treated in deionized (DI) water for 5 minutes at various temperatures, including 75 °C, 85 °C, and 95 °C. Concentrations of Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus epidermidis (S. epidermidis) were placed on Al foil for different times, ranging from 30 seconds to 60 minutes. The survival time was measured, and the analysis of the results indicates a direct correlation between when the bacteria was exposed to HWT Al foil and the number of bacteria killed. As the temperature of the HWT increased, there was an increase in antibacterial activity. This finding is consistent with our expectations; at higher HWT temperatures, more prominent nanostructures are produced, causing increased inactivation of bacteria. Our results show the nanostructured HWT Al foil was superior at inactivating Gram-negative (E. coli) and Gram-positive (S. epidermidis) bacteria compared to the untreated control Al foil. HWT Al foil treated at 75 ℃, 85 ℃, and 95 ℃ was 58%, 64%, and 73% more effective in killing the Gram-negative bacteria, respectively, after only 30 seconds of contact time compared to untreated control Al foil, while the antibacterial efficacy was enhanced 88%, 92%, and 94% for the Gram-positive bacteria, respectively. The HWT nanostructures synthesized at 95℃, after 60 minutes of contact time, were able to inactivate 97% of the gram-negative bacteria and 100% of the gram-positive bacteria, demonstrating the efficacy of its antibacterial properties. This research presents a novel, inexpensive, and environmentally friendly method of producing nanostructures that inhibit bacterial activity.