Shooting bacteria with a silver bullet

It has been known for some time that silver is highly toxic to a wide range of bacteria, and silver-based compounds have been used extensively in bactericidal applications.

This property of silver has caused great interest especially as new resistant strains of bacteria have become a serious problem in public health.

For example MRSA bacteria kill 5,000 hospital patients a year in the UK alone and any method of attacking them, not involving normal antibiotics, is becoming increasingly important.

Silver in the form of nanoparticles is even more effective, partly because of the high surface/volume fraction so that a large proportion of silver atoms are in direct contact with their environment. In addition, nanoparticles are sufficiently small to pass through outer cell membranes and enter cells' inner mechanisms.

A recent study showed that only silver nanoparticles with sizes less than 10 nm (1,000 times smaller than the width of a human hair) were able to enter cells and disrupt them. The same study showed that silver nanoparticles are highly toxic to the bacteria that colonise the lungs of cystic fibrosis sufferers often with fatal consequences.

Professor of Nanoscience at the University of Leicester, Chris Binns, commented: "One of the problems, however, is in getting assemblies of nanoparticles of the same size into the right environment, for example on the surface of a wound dressing or in a colloidal suspension that can either be turned into an aerosol or injected into the body.

"The studies carried out so far acknowledge that in existing commercially available nanoparticle suspensions, only 1% of the material consists of nanoparticles of the right size."

"With support from the "Higher Education Reach "Out to Business and the Community Innovation and Regional Fund' (HIRF) this is now being put to good use to develop a machine specifically to produce nanoparticle assemblies for medical applications. The impressive uniformity of silver nanoparticles produced by the source is illustrated in the figure (available on request) and the design enables the nanoparticles to either be coated onto a solid surface or incorporated into a liquid suspension," Binns said.

Trials of the anti-microbial effectiveness of the nanoparticle suspensions will begin shortly.