Kaiming Ye, chair of the Department of Biomedical Engineering, and Associate Professor Guy German developed a machine to disinfect personal protective equipment such as facemasks. Credit: Jonathan Cohen
A new study from scientists at Binghamton University supports previous research regarding the best UV wavelength to deactivate SARS-CoV-2, but falls short of agreeing that 222 nanometers (nm) is completely harmless to humans.
“There is a lot of research on UV dosages in the scientific literature, but not in a systematic way,” said Kaiming Ye, chair of the Department of Biomedical Engineering and lead author of the study. “The system we came up with can become the model for anybody who wants to standardize the dosage. This is how to determine the eradication of SARS-CoV-2 using UVC—maybe also SARS-CoV-3, SARS-CoV-4, SARS-CoV-5. We hope we never get there, but we need to be prepared.”
There are three UVC range subsets that have been extensively studied as optimal for pathogen disinfection: 207 to 222 nm; 254 nm; and 260 to 280 nm. The 254 nm wavelength is the most commonly used, but it is damaging to human skin and eyes so it can only be done in unoccupied rooms. For that reason, during the pandemic, many turned to the effectiveness of 222 nm wavelength light, which has been reported to not penetrate tissue as deeply as its higher wavelength UVC counterparts.
However, in their study published in Scientific Reports, Ye and his team found that the 222 nm light does in fact have some affect on the human skin. Additionally, the researchers discovered that the disinfection efficiencies of the wavelengths are greatly influenced by the media where the virus is contained—something not previously considered.
In the study, the Binghamton team added a retrovirus similar to SARS-CoV-2 to three different media—a cell-culture medium, water and an artificial re-creation of human saliva. They then exposed each to three different wavelengths—222 nm, 254 nm and 265 nm.
According to the results, the disinfection efficiencies highly depended on the type of media. The researchers observed a higher susceptibility of the virus to 222 nm UVC light in phosphate buffered saline (PBS) compared with 254 and 265 nm light. This suggests that 222 nm is more effective than 254 nm when UVC-absorbing elements are absent. However, in highly UVC-absorbing liquids, such as cell culture medium with serum, 265 nm was the more effective wavelength.
“We discovered absorbance and susceptibility are inversely correlated with each other, whether due to the material or change in the optical pathlength,” the researchers explain. “Inactivation studies often employ liquids commonly present in laboratories. Our work suggests that the adoption of more relevant liquids such as saliva may give more physiologically relevant and meaningful inactivation dosages.”
Ultimately, based on the results, the researchers believe a dual wavelength approach of 222 nm plus broad-spectrum UV source centered around 265 nm would provide the more robust disinfection system.
The team also investigated the safety of different UVC light sources. While they did not observe significant decreases in the stiffness of skin exposed to either 254 nm and 222 nm, there were decreases to the fracture stress, fracture strain, and work of fracture.
“We demonstrated that both far (222 nanometers) and regular UVC light (254 nanometers) degrade the mechanical integrity of the stratum corneum, the skin’s top layer, causing higher likelihood of cracking. That means nasty bacteria and other microorganisms can get into and potentially infect your skin,” explained Binghamton associate professor and study author Guy German.
Based on the results of the research, Ye and German have designed an LED light disinfection system that should cause less damage to human skin. They are doing additional testing before applying for a patent on it.
“We are waiting for the data, and then we are pretty much finished. We know it will work,” said Ye.