New plastic film to tackle E. coli

Chemical Engineers in Switzerland have created a plastic film that's up to 1000 times more effective at killing E. coli bacteria cells than conventional methods.

The team from the Swiss Federal Institute of Technology, Zurich have discovered that coating the film with a mix of silver and calcium phosphate nano-particles proves deadly to bacteria.

Wendelin Stark, a chemical engineer and leader of the project explained that it had been previously impossible to apply silver in a targeted and measured way. However, by using a film and applying the silver to the calcium phosphate, he believes the problem has been overcome: "Within 24 hours of the plastic film being applied to a surface, less than 1 bacterium out of 1 million bacteria will survive."

Because bacteria rely on calcium for their metabolism, the 20-50 nanometer calcium phosphate particles are used by the micro-organisms as nutrition. When the bacteria consume the calcium phosphate, this releases thousands of small silver 1-2 nanometer particles. It's these tiny silver particles that kill the bacteria and prevent germs from growing and spreading.

The polymer film only emits silver if bacteria are growing in the vicinity. This can be assessed by the quantity of calcium phosphate that is taken up by the bacterium. "It saves money and is much more efficient," said Stark.

"It also reduces the environmental impact of the process and we have developed a method that is easy to apply and could bring great benefits to patients in hospitals, as well as the food industry."

Silver has been used as an antiseptic and disinfectant for thousands of years. Wealthy households would commonly use silver tableware in the belief it could fend off germs, whilst poorer people would put silver coins into their milk jug.

Silver was also used in medical treatments before being replaced by antibiotics but nanotechnology has allowed the metal something of a medical renaissance. The project is now being up scaled by a Swiss Company.

The work has been praised by Dr David Brown, Chief Executive of the Institution of Chemical Engineers: "This is an outstanding example of how chemical engineers are making a crucial contribution to society".

Details of the work have been published in the science journal, Small with a second paper due for publication in Nature Nanotechnology next month.