New Curtin research has found that gold and copper could become weapons in the fight against COVID.
The study, published 7 March 2023 in Chemical Science, showed that the spike proteins of SARS-CoV-2 become trapped when they encounter silicon, gold and copper, and that electric fields can be used to destroy the spike proteins, likely killing the virus.
In 2020, it was reported that the viability of the SARS-CoV-2 virus in aerosol droplets varied on different surfaces. While the virus remained viable for three days on plastic, cardboard, and stainless steel, it was only viable for three hours on copper.
Although the study highlighted the effect of surfaces on the lifespan of the viral particles, the reason of its low viability on copper compared to other surfaces remained unknown.
Lead researcher Dr Nadim Darwish, from Curtin’s School of Molecular and Life Sciences, said the study examined how the spike proteins of coronaviruses attached and became stuck to certain types of surfaces.
“Coronaviruses have spike proteins on their periphery that allow them to penetrate host cells and cause infection and we have found these proteins becomes stuck to the surface of silicon, gold and copper through a reaction that forms a strong chemical bond,” Dr Darwish said.
“We demonstrated that SARS-CoV-2 spike protein reacts and forms covalent bonds with specific metals and Si. Metal surfaces that have affinity to thiols/disulphides such as Au, Pt and Cu covalently bond to the spike protein via M–S bonding.”
Initial research revealed that the structures of the spike proteins (S1 and S2) of most of the coronaviruses, including SARS-CoV-2, are proteins that possess multiple disulphide (S–S) bonds, and their abundance indicates their key role in the formation and stabilisation of the spike’s architecture.
These S–S bonds are essential for the SARS-CoV-2 spike protein structure and its ability to infect human cells, by interacting with the angiotensin-converting enzyme 2 (ACE2) human cell surface receptor via a thiol–disulphide exchange process.
On surfaces, S–S residues have been reported to form covalent bonds to noble metals such as Au, and oxide-free silicon (Si-H) and recently, it has been demonstrated that Si–H surfaces can spontaneously reduce the S–S bonds in a disulphide-terminated organic molecule, connecting these molecules to the Si surface via covalent S–Si bonds.
The team used surface spectroscopy, electrochemical and single-molecule scanning tunnelling break junction techniques to study the chemical reactivity of SARS-CoV-2 with surfaces of electrodes, electrically detect the spike protein and study the effect of electric fields on spike proteins at the level of a single-molecule.
The spike protein was found to be washed away from mica surfaces which did not form a covalent bond with the S-S protein, with the same result reported for plastic and stainless-steel surfaces that had been incubated with the spike S1 protein – and the protein remains only physically adsorbed on these surfaces.
However, the protein azurin, which has only one S–S at one of the very peripheral ends and a copper metal centre at the opposite terminal, formed S–Si bonds with Si surfaces and similarly, XPS of the spike S1 protein on Pt and Cu surfaces showed covalent bonding between the protein S–S bridges and these metals.
“This covalent bonding potentially explains why SARS-CoV-2 survives a limited amount of time on copper compared to its viability on stainless steel and plastics,” the study said.
“Such a mechanism would involve the oxidation of the Si–H surfaces at the nanoscale by water vapour from the ambient environment, generating electrons that break the disulphide bonds in the spike protein.
“On metal surfaces, the mechanism is suggested to be different to that on Si, with the electrochemical reduction scenario not possible due to the high reduction potential of the Au, but with the same outcome of Au–S covalent bonding.
“The reaction of S–S in SARS-CoV-2 with metals and Si is particularly relevant because all previous and likely future coronaviruses will possess peripheral disulphide bonds in their spike proteins.”
Dr Darwish believed these materials could be used to capture coronaviruses by being used in air filters, as a coating for benches, tables, and walls or in the fabric of wipe cloths and face masks.
“By capturing coronaviruses in these ways, we would be preventing them from reaching and infecting more people,” he said.
Co-author PhD candidate, Essam Dief, Dr Darwish’s colleague from the School of Molecular and Life Sciences, said the study also found the coronavirus could be detected and destroyed using electrical pulses.
“We discovered that electric current could pass through the spike protein and because of this, the protein can be electrically detected,” Mr Dief said.
“In the future, this finding can be translated to involve applying solution to a mouth or nose swab and testing it in a tiny electronic device able to electrically detect the proteins of the virus. This would provide instant, more sensitive, and accurate COVID testing.
“Even more exciting, by applying electrical pulses, we found the spike protein’s structure is changed and at certain magnitude of the pulses, the protein is destroyed. Therefore, electric fields can potentially deactivate coronaviruses.
“So, by incorporating materials such as copper or silicon in air filters, we can potentially capture and consequently stop the spread of the virus, but importantly, by incorporating electric fields through these filters for example, we also expect this to deactivate the virus.
“The study is exciting both fundamentally, as it enables a better understanding of coronaviruses, and from an applied perspective in helping to develop tools to fight the transmission of current and future coronaviruses.”