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Light-Activated Coating Kills Bacteria, Even in Dark

Samples of silicone with various dyes infused

Samples of silicone with various dyes infused (Sacha Noimark, Elaine Allan and Ivan P. Parkin, University College London)

25 March 2014. Chemistry researchers at University College London in the U.K. developed a material that when coated on surfaces in the lab can kill bacteria when exposed to light, as well as in total darkness. The team led by UCL chemistry professor Ivan Parkin published its findings online earlier this month in the journal Chemical Science (paid subscription required).

The research was funded by Ondine Biomedical in Vancouver, British Columbia, Canada that first licensed UCL’s research in 2008. In 2011, Ondine and UCL received a grant of £1 million ($US 1.65 million) from the U.K.’s Medical Research Council to develop a light-activated anti-microbial application to prevent catheter-associated infections. UCL holds a patent on the technology.

Parkin and colleagues from UCL’s chemistry department and dental school designed the technology to meet the need for better tools to control infections in health care facilities, those acquired by patients in hospitals and clinics. According to the U.S. Centers for Disease Control and Prevention, about 1 in 20 hospitalized patients gets an infection when receiving medical care. Even with stringent cleaning and hand-washing policies, infections in hospitals remain difficult to control.

The UCL researchers address the problem differently, by creating surfaces hostile to microbes, to keep pathogens from accumulating on surfaces of equipment, keyboards, and door handles. The technology combines gold nanoparticles mixed with known anti-microbial dyes that react to light. As Parkin explains in a university statement, “The light excites electrons in them, promoting the dye molecules to an excited triplet state and ultimately produces highly reactive oxygen radicals that damage bacteria cell walls.”

The team still had to solve the problem of binding this anti-microbial compound to surfaces and equipment used in hospitals and clinics. They found a simple method of infusing silicone polymer rubber used on a wide variety of medical equipment with a solvent that swelled the silicone to penetrate the anti-microbial compound into the material. They then dipped the infused material into the compound to form a a thin layer on the surface, that in tests remained stable even when wiped with alcohol or exposed to light.

The UCL researchers tested combinations of crystal violet and methylene blue dyes mixed with gold particles as small as 2 nanometers — 1 nanometer equals 1 billionth of a meter. The tests were conducted with E. coli and Staphylococcus epidermidis bacteria known to form on catheters and other hospital devices, and under realistic lighting conditions, such as fluorescent lights.

Even with quantities of bacteria far greater than found in hospitals, say the researchers, the treated surfaces were able to kill all of the bacteria in 3 to 6 hours. As lead author and postdoctoral researcher Sacha Noimark notes in a university statement, they were surprised to discover a sample left in the dark also “showed significant reductions in bacterial load, albeit over longer timescales of about 3 to 18 hours.”

Ondine Biomedical’s technology platform, called photodisinfection, uses lasers to activate anti-microbial activity on surfaces. This new discovery, if developed further by Ondine, would expand its capabilities into activation under normal lighting conditions.

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