Antibacterial surface active even in the dark

The combination of two simple dyes together with gold nanoparticles is lethal to the bacteria when exposed to light - even at low lighting levels found inside buildings such as hospitals

Researchers from University College London (UCL) have developed a new antimicrobial agent that has the potential to reduce hospital-acquired infections. The combination of two simple dyes together with gold nanoparticles is lethal for the bacteria when exposed to light - even at low lighting levels that exist inside buildings. The new combination activity is effective even in total darkness. The research findings were published in the scientific journal Chemical Science.

Infections that develop in hospitals are a serious problem in modern medicine, when strains of bacteria that are resistant to antibiotics are gaining increasing popularity. Although medical institutions have strict and strict disinfection policies, insisting on frequent hand washing of workers, and are stockpiles of powerful drugs, it is difficult to eradicate these infections unless you make the hospital environment hostile to the bacteria. Various surfaces, such as those of doorknobs, medical equipment, keyboards, pens, etc. are easy routes for the spread of bacteria, even for hands that have just been washed.

One possible solution to this problem is to develop alternative strategies such as antimicrobial coatings that make surfaces less friendly to infections. These surfaces are not similar to antibacterial liquids that just wash out the contaminants - the goal is to make the surface inherently lethal to the harmful bacteria.

"There are a number of dyes known to be harmful to bacteria when exposed to bright light," explains lead researcher Ivan Parkin (director of the chemistry department at the research institute). "The light excites their electrons in these substances, raises the color molecules to the state of an excited triplet and ultimately causes the creation of highly active oxygen radicals that destroy the cell walls of the bacteria. As part of our project, we tested new combinations of such color materials together with gold nanoparticles, and we also made the ways to treat such surfaces simpler, which will make our technology simpler and cheaper."

The research team examined several different combinations of the dyes crystal violet (already used today to treat bacterial infections) and methylene blue together with nano-gold to coat the surface of silicon. This flexible material is commonly used as a sealant, coating as well as for building medical devices such as tubes, catheters, gaskets, and is also used inside cases that protect various objects such as keyboards and telephones.

While previous studies dealing with the creation of antimicrobial surfaces often focused on the complex ways of attaching the dyes to the surface, this study chose a simpler approach. The researchers used an organic solvent designed to swell the silicone, while bubbling the dye molecules and gold nanoparticles into the polymer. In the next step, they dipped this silicon in a solution of the crystal violet dye to create a thin layer of dye on top of the polymer surface.

In their experiments, where the contaminated surfaces were exposed to lighting levels similar to those used in hospital buildings, surfaces treated with the combination of crystal violet, methylene blue and nano-gold exhibited the best antimicrobial effect ever observed for this type of surface. Moreover, the treatment did not result in a significant change in the properties of the silicone (for example, its water repellency level), and the coating was not affected by pouring alcohol on it, which means that it will be able to withstand the repeated cleanings carried out in hospitals, without wearing it out.

"Even though we contaminated the surface with an amount of bacteria tens of times higher than the level that exists in hospitals, and exposed it to normal fluorescent lighting conditions, all the bacteria were eliminated within 6-3 hours, depending on the type of bacteria," said the chief researcher. "That in itself was a great result, but the bigger surprise came with the sample we left in the dark. This sample also showed a significant reduction in the amount of bacteria, although it took much longer, ie 8-3 hours. Still, the exact mechanism within which this bacterial eradication takes place in the dark is still unclear." This is the first time that an antibacterial surface activated by light has shown an active result in the dark. This result, together with the unprecedented performance under normal hospital lighting conditions, and the relatively simple and inexpensive manufacturing processes, mean that this technology holds great promise for future applications.

The news about the study