First surface that kills deadly bacteria even in dark

Scientists have developed the world's first light-activated antimicrobial surface that can kill deadly bacteria even in the dark and may help cut hospital acquired infections.
The combination of two simple dyes with nanoscopic particles of gold is deadly to bacteria when activated by light - even under modest indoor lighting.
And in a first for this type of substance, it also shows impressive antibacterial properties in total darkness, researchers said.
Hospital-acquired infections are a major issue for modern medicine, with pathogens like methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile (C diff) getting extensive publicity, they said.
It is difficult to eliminate these infections unless you can make the hospital environment more hostile to microbes.

"There are certain dyes that are known to be harmful to bacteria when subjected to bright light," said corresponding author Ivan Parkin from University College London.

"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.
"Our project tested new combinations of these dyes along with gold nanoparticles, and simplified ways of treating surfaces which could make the technology easier and cheaper to roll out," said Parkin.
The team, tested several different combinations of the dyes crystal violet, methylene blue and nanogold, deposited on the surface of silicone.

The researchers used an organic solvent to swell the silicone, allowing the methylene blue and gold nanoparticles to diffuse through the polymer.
They then dipped the silicone into a crystal violet solution to form a thin dye layer at the polymer surface.
In their tests, in which infected surfaces were subjected to light levels similar to those measured in hospital buildings, surfaces treated with a combination of crystal violet, methylene blue and nanogold showed the most potent bactericidal effect ever observed in such a surface.
"Despite contaminating the surface with far more bacteria than you would ever see in a hospital setting, placed under a normal fluorescent light bulb, the entire sample was dead in three to six hours, depending on the type of bacteria," said the research paper's lead author, Sacha Noimark.

"That was an excellent result, but the bigger surprise was the sample which we left in the dark," said Noimark.
The finding was published in the journal Chemical Science.