European scientists have created light-activated antimicrobial surfaces by modifying a material used in medical devices with tiny amounts of commonly used dyes.

Silicone is used in medical equipment, such as catheters. But bacteria can colonise its surface so that infections associated with catheter use are very common. Ivan Parkin, Mike Wilson, at University College London, and their colleagues in the UK and Spain have modified the polymer so that it kills bacteria when it is irradiated with a laser or visible light.

Lasers and dyes can kill bacteria

The researchers covalently bound organic dye molecules, methylene blue or toluidine blue O, to silicone surfaces. The process involves dipping a modified silicone in a solution of the dye for 24h, washing and drying it. It uses only small amounts of the dyes (picograms per mm2) but is very effective. After a few minutes' exposure to a low power laser, levels of viable Escherichia coli and Staphylococcus epidermidis on the polymeric surfaces dramatically drop: up to 99.999 per cent in the case of S. epidermidis.

The dyes work by generating reactive oxygen species under light irradiation and it is these that are toxic to the bacteria. The dyes have been incorporated into silicone before, but not covalently so they could potentially leach from the polymer.

Previous methods to sterilise catheters include using silver coatings - an expensive method - or flushing the catheters with antibiotics. However, using antibiotics persistently can make bacteria resistant to the drugs. 'This [technique] would strengthen the lifetime you could use antibiotics for,' says Parkin. Not only catheters, but antimicrobial keyboards or telephones made of these materials could soon be possible, which 'would be especially important to minimise infections in hospitals,' suggests Parkin.

For Declan McCormack, an expert in materials chemistry from the Dublin Institute of Technology, Ireland, the coating's importance is clear. 'Parkin's work is an interesting and novel strategy in developing effective antimicrobial coatings for medical surfaces,' he says. 'It is a significant advancement in functional coatings.'

Amaya Camara-Campos

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