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The COVID-19 pandemic has made people more aware of surfaces' role in the spread of a virus. However, it is not only viruses that can adhere to surfaces. Bacterial and fungal spores can also survive for an extended period on various surfaces and help spread infections. Researchers have recently developed a novel nanocoating, inspired by the architecture of a dragonfly's wings, to develop a surface disinfectant.
Pathogen survival outside the body and on surfaces are significant issues, especially in hospitals and public places. Pathogens on surfaces may lead to the emergence and spread of antimicrobial resistance. In 2016, a survey of more than 48,000 patients in England was conducted, among which 6.6% of patients acquired infection during their stay in the hospital. Researchers have devised many technologies to curb infection transmission via surfaces, such as developing an engineered surface that is toxic to bacteria, creating efficient nanocoatings with antimicrobial efficacy, and chemical disinfectants.
Antibacterial Nanocoating
As a single kind of engineered surface cannot destroy all types of bacteria, researchers have been studying various spiky particles impregnated on the surfaces (nanocoating) and analyzing their effect on bacterial growth.
Surface charge also plays a vital role in the antibacterial property of a surface. This is because several bacteria carry a negative surface charge. Therefore, if the nanoneedles impregnated on a surface are positively charged, the negatively charged bacteria will travel towards the surface due to electrostatic attraction.
Silicon-carbon-based nanocoating is an interesting material as it can be attached to different kinds of surfaces, i.e., hard and soft. This broadens its application to carpets, clothing, bed rails, and plastic tubes.
Researchers have been keen to develop means to regulate the surface charge of organosilanes to improve their applicability. However, some scientists have recently pointed out the ineffectiveness of organosilane coatings against many bacteria. This may be due to the composition of the bacterial cell wall that makes them resistant to the nano spike.
Scientists believe that the application of nanocoatings on existing surfaces and equipment that are frequently touched in hospitals or other public places could significantly minimize the transmission of infection. As it does not require any replacement of objects or equipment, this technology is regarded as simple and cost-effective.
How do Wings of Dragonfly Kill Microbes?
The wings of dragonflies and cicadas inhibit bacterial growth due to their natural structures. A microscopic study has revealed that their wing's surface contains nanopillars or nano spikes that look similar to a bed of nails. The tiny spike-like structures invisible to human eyes, are deadly to many bacteria such as Bacillus subtilis, Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. These are the pathogenic bacteria that are commonly associated with various hospital-acquired infections. The tiny spike-like structures or nano-needles puncture the bacterial cell walls, destroying the bacterial cells. These nanostructures also cause internal damage through the release of free radicals.
Dragonfly-Inspired Nanocoatings
British Columbia Centre for Disease Control stated that hands transmit around 80% of common infections. Therefore, disinfecting the commonly touched surfaces would prevent the spread of harmful pathogens. Dr. Yugen Zhang and his team have created a novel nanocoating that can spontaneously kill bacteria upon contact.
Studies on dragonflies and cicadas inspired researchers. They developed nanopillars of zinc oxide, which contain antibacterial and non-toxic properties. The zinc oxide nanocoating can inhibit the growth of wide-ranging harmful bacteria such as E. coli and S. aureus, which are commonly transmitted through surface contact.
The zinc oxide nanocoating was tested on various objects such as glass, ceramic, and titanium. The coating significantly killed up to 99.9% of bacteria found on the surfaces. This technology is also environment friendly as the bacteria are killed mechanically and not chemically.
Another advantage of zinc oxide coatings is that the development of resistant bacteria can be prevented. The zinc oxide nanocoating destroys the bacteria by damaging its cell walls with the nanospikes. They also catalyze the release of superoxides and other free radicals, which kill surrounding free-floating bacteria, that were not directly connected with the surface.
The dual mechanism, i.e., a) mechanical properties of the nanopillars and b) antibacterial effects of zinc oxide, broadens the scope of coating applications in various surfaces, hard or soft.
The research team has also found that this technology is useful in water containing E. coli. Therefore, this technology can also be used for water purification.
IBN has recently received a grant from the National Research Foundation, Prime Minister’s Office, Singapore, to further advance nanocoating technology. They have also collaborated with Tan Tock Seng Hospital for commercial application over the next five years.
References and Further Readings
Guangshun Yi et al. (2018) ZnO Nanopillar Coated Surfaces with Substrate-Dependent Superbactericidal Property. Small. 14(14).1703159. DOI: 10.1002/smll.201703159
Geddes, L. [Online] Imperial College London. Antimicrobial surfaces. Available at: https://www.imperial.ac.uk/stories/antimicrobial-surfaces/
Agency for Science, Technology and Research (A*STAR) (2018) Dragonfly-inspired nano coating kills bacteria upon contact by Singapore. Available at: https://phys.org/news/2018-03-dragonfly-inspired-nano-coating-bacteria-contact.html
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