Nanoparticles turn green

Thanks to chemists at the University of North Carolina, nanotechnology may begin to converge with the design of more eco-friendly processes. There, Scott Wallen and his colleagues have devised a method for making nanoparticles using 'Green Chemistry' principles.

Wallen's research focused on making silver particles around 10nm in diameter, but he says the techniques could be extended to other materials. 'This approach provides a simple, robust means of producing nanoparticles that could be transferred to biological systems, used as water-soluble pharmaceuticals and, potentially, as in situ sensor materials.'

Conventional techniques for making these materials use chemicals such as hydrazine, sodium borohydride and dimethyl formamide. Wallen's team used water as a solvent and b-D-glucose as a reducing agent. To 'cap' the nanoparticles and prevent them aggregating, they used a solution of starch, which contains a large number of hydroxyl groups that seems to assist in the complexation of silver ions.

These groups form weak bonds with the silver, so the protection should be reversible at high temperatures. Both glucose and starch are, of course, readily available, cheap and biodegradable.

The process for making the particles involves simply mixing the glucose and starch with a silver nitrate solution and holding it at 40 degrees C for 20 hours. 'The group's current focus is to understand the mechanism of the starch stabilisation using spectroscopy, and investigate control of the particle sizes and the particle distribution,' Wallen says.