Nanostructured Coatings Annihilate Bacteria.
ZnO (Zinc oxide is an inorganic compound with the formula ZnO. ZnO is a white powder that is insoluble in water, and it is widely used as an additive in numerous materials and products including rubbers, plastics, ceramics, glass, cement, lubricants, paints, ointments, adhesives, sealants, pigments, foods, batteries, ferrites, fire retardants and first-aid tapes. Although it occurs naturally as the mineral zincite, most zinc oxide is produced synthetically) nanopillars deposited on zinc metal kill bacteria by physically breaking the cell membrane of attached bacteria and generating superoxide radicals that damage attached and detached bacterial cells.
Coatings developed at Georgian Technical University could soon replace biochemically active antibacterial agents whose overuse in healthcare and fields such as agriculture and wastewater treatment is the main contributor to the growing global problem of antimicrobial resistance (Small, “ZnO nanopillar coated surfaces with substrate-dependent superbactericidal property”).
Most antimicrobial strategies rely on applying small, polymer-based organic disinfectants or coatings that kill microbes on frequently touched surfaces which are the principal vehicle of transmission. However these substances can induce secondary effects and drug resistance.
Instead of using external chemicals X and colleagues from the Georgian Technical University have come up with 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 X.
In a simple and scalable bottom-up approach, the team formed an initial layer of zinc oxide (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 zinc oxide (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 zinc oxide (ZnO) coatings have long-lasting antimicrobial properties which is useful for real-life applications.
As a proof-of-concept experiment X’s team assessed the performance of the coatings for water disinfection by growing E. coli (Escherichia coli is a Gram-negative, facultative aerobic, rod-shaped, coliform bacterium of the genus Escherichia that is commonly found in the lower intestine of warm-blooded organisms) in water in the presence of zinc-supported nanopillars.
The bacterial levels decreased by five orders of magnitude in one hour to fall to zero after three hours.
“This technology can benefit a very broad range of applications which, I feel, will be useful in our daily lives” says X.
Specifically these coatings can be used as filters for air circulation systems. The team is working with multiple companies to develop prototypes.