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Zinc oxide nanopillars deposited in surface coatings impale bacteria on nanospikes
October 07, 2018
Source: ASM International
The A-Star Institute of Bioengineering and Nanotechnology (IBN), Singapore, reports that its researchers have developed nanostructured coatings that annihilate microbes by piercing their cell walls. The coatings consist of ultra-small zinc oxide (ZnO) spikes, or nanopillars.
“We were inspired by the wings of dragonflies and cicadas, which prevent bacteria from adhering to their surfaces because they are covered with minuscule spikes,” says IBN Group Leader Dr Yugen Zhang. The zinc oxide nanopillars can kill a broad range of germs such as E. coli and S. aureus that are commonly transmitted from surface contact.
In a simple and scalable bottom-up approach, the team formed an initial layer of ZnO particles on various substrates, such as glass, ceramics, zinc foil, and galvanized steel, and grew the nanopillars on these ‘seeds’ from an aqueous solution of zinc salts.
To their surprise, the coatings demonstrated excellent antimicrobial activity against the gram-negative bacteria Escherichia coli and gram-positive Staphylococcus aureus, as well as the fungus Candida albicans, especially when deposited on zinc foil and galvanized steel.
Fluorescence and electron microscopy revealed that, in addition to physically rupturing the cell walls of surface-attached microbes, nanopillars formed on these zinc-based substrates had another benefit. Specifically, the electron transfer between the zinc substrate material and the ZnO pillars generated strong superoxide radical oxidants which chemically damaged both attached and detached microbial cells. This enhanced the potency of the nanopillars compared to those deposited on other substrates.
In addition to their stability and lack of toxicity, these ZnO coatings have long-lasting antimicrobial properties, which is useful for real-life applications. As a proof-of-concept experiment, Dr. Zhang’s team assessed the performance of the coatings for water disinfection by growing E. coli in water in the presence of zinc-supported nanopillars. The bacterial levels decreased by five orders of magnitude in one hour and fell to zero after three hours.
The researchers report their results in an article in the journal Small, "ZnO nanopillar coated surfaces with substrate-dependent superbactericidal property".
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