Portable Virus Disinfection Within Reach

DOUGLAS FARMER, SENIOR EDITOR
doug.farmer@photonics.com

With the rapid spread of the virus that causes COVID-19 and others, researchers, clinicians, custodial staff, and the general population are looking for the most efficient way to disinfect surfaces and other areas where the virus may reside and have a significant impact on public health. Many products have become scarce as professionals and the public have grappled with how to keep living and working quarters safe during the ongoing pandemic.

A collaboration of academics from the U.S. and Japan have concluded that the solution may be to bathe these spaces in ultraviolet light with the aid of strontium niobate, or SrNbO₃. Those involved in the project work at Penn State University, the University of Minnesota, Tohoku University, and the University of Tokyo.

Traditionally, the most common methods to decontaminate an area from viruses and bacteria are chemicals or ultraviolet radiation. While the former haven’t been easy to come by in recent months, the latter often requires a bulky system using a mercury-containing gas discharge lamp. Those involved in recent research, however, realized that UV-emitting diodes could prove to be part of the answer for the construction of more mobile equipment.

Roman Engel-Herbert, an associate professor of materials science, physics, and chemistry, explained that enough UV light had to hit an area to kill all viruses present. Joseph Roth, a doctoral candidate in materials science and engineering under the tutelage of Engel-Herbert, said the length of time it needed to be used in an area was dependent on the UV light intensity.

“The CDC recommends a 1.8-J/cm² dose to reach an antimicrobial efficacy of 99.9% for influenza and coronavirus strains,” Roth said. “This means a UV light with an irradiance of 100 mW/cm² would take 18 seconds to disinfect a surface.”

To be effective, the electrode itself needed to be transparent to UV light, to maximize transmission. Roth said they were aware that their Japanese counterparts had been experimenting with SrNbO₃ for various purposes, and the group was excited to see if it could prove viable in this context.

“UV disinfection using mercury vapor lamps is quite common,” Roth said. “This technology has most commonly been used in hospitals for disinfection, but with the recent pandemic its usage has been expanded to disinfect public spaces such as the New York City metro and the Shanghai public transit.”

In their study, researchers discussed the challenges of working with LED light in the UV spectrum (260 to 320 nm), such as low external quantum efficiency and the current lack of a transparent electrode material. Both need to be improved to create a portable unit to be used in a variety of settings, such as HVAC systems in buildings, theaters, and public transit systems.

But fortunately, they discovered that SrNbO₃ works well as a conductor in the visible and UV range. Various samples of this material were grown at varying thicknesses and were studied. The researchers determined that strontium niobate has a combination of high transmission and conductivity, which would enable effective, long-lasting, and portable uses.

“The technology is only dependent on a highly efficient UV LED array and a battery to power it, so it could be compared to the size of anything that can house those two components,” Roth said.

The researchers believe their research could lead to further applications in UV sanitation, biomolecule sensing, UV phototherapy, UV curing, UV photolithography, and solar blind detector technology.

This research was published in Communications Physics (www.doi.org/10.1038/s42005-020-0372-9).