Engineers from the University of Massachusetts Amherst (UMass Amherst) have created an ultraviolet (UV) ray-emitting glass that reduces the build-up of biofilm — a slimy layer of assorted microorganisms that grows on wet surfaces — from forming on underwater surfaces.

Because biofilm formation on underwater surfaces like ships increases a ship's drag, subsequent fuel usage, and corrosion damage on ships or oceanographic equipment as well as fogs up windows used for cameras and other sensing devices and transports non-native species across the seas, the engineers sought out a solution that didn’t involve commonly used chemical agents like biocidal coatings, which threaten ecosystems.

The glass treated with ultraviolet rays (inside), had 98% less biofilm growth than the untreated glass (outside). Source: University of Massachusetts Amherst

To accomplish this, the UMass Amherst team created biofilm-resistant glass using UVC radiation — which is reportedly the shortest and most effective and disinfecting wavelength of UV radiation.

The team previously demonstrated that UV side-emitting optical fiber can distribute UVC radiation in small channels — such as medical equipment, including endoscopes, catheters and respirators; home devices including coffee makers and refrigerators; and water storage/distribution systems including pipes, bladders and membranes — to destroy pathogenic organisms and subsequently prevent bacteria growth on surfaces.

This earlier approach of using a light source to evenly distribute UV light on a surface, however, would not necessarily work in an underwater environment. Among the assorted reasons for this, the team added, is that light is weaker as it travels away from the source, which makes it challenging to cover large surface areas. Further, UV waves can also be disturbed by surrounding water that is murky.

Consequently, this uneven distribution of UV light enables biofilm-forming microorganisms to gain a foothold, thereby leaving the entire surface vulnerable to biofilm attachment, which can then spread to other parts of the surface.

To address this, the team applied a silica-nanoparticle coating to glass.

"The UV LED is connected from the cross-section of the glass," the researchers described. "As UV enters the glass, we scatter the UV from inside of the glass to the outside," via light-scattering nanoparticles. The silica does not absorb the UV rays and the waves proceed to bounce off the nanoparticles and through the glass interior, thus allowing an even "glowing" glass surface.

The engineers tested the UV-emitting glass by submerging it in water for 20 days. When measured against untreated glass, the researchers reported that the UV-emitting glass reduced visible biofilm growth by roughly 98%.

The team is eyeing the technology for the future disinfection of transparent surfaces — including windows of ships, flotation spheres and moored buoys, camera lenses and sensors for oceanographical, agricultural and water treatment applications.

The technology is detailed in the article, “A promising strategy for biofilm inhibition on transparent surfaces,” which appears in the journal Biofilm.