Silver nanoparticles can provide a highly sensitive colorimetric method to detect melamine in infant formula claim Chinese scientists. 

The China milk scandal in 2008 when 300,000 infants became victims of melamine, a chemical usually used in fire retardants and fertilizers, contaminated milk and infant formula highlighted the need for the country to improve detection standards for chemical contaminants in foods. 

Several improved techniques were developed following the crisis but they involved large specialised equipment, such as mass spectrometers. Now, Cuiping Han and Haibing Li at the Central China Normal University, Wuhan, have developed a silver nanoparticle sensor that changes colour from yellow to dark green in the presence of melamine. As the result can be seen with the naked eye, no other specialist lab equipment is required making the test more portable. 

'The unique instrument-free detection feature of this colorimetric method could allow for on-site detection of melamine and offers great potential for household diagnostic applications' say the researchers. Colometric methods using gold nanoparticles have been tried previously but they require an additional stabilizer to detect the melamine which is difficult to synthesize and limits their practical application, explain Han and Li. 

The silver nanoparticles are modified with p-nitroaniline (p-NA) and are easily prepared using commercially available materials. The electron donor-acceptor interaction between the melamine (donor) and p-NA (acceptor) results in aggregation of the silver nanoparticles, causing the colour change and allowing melamine levels as low as 0.1 ppm to be detected in as little as two minutes. 

Paolo Ugo, a specialist in nanoelectrochemistry and sensors at the University of Venice Ca' Foscari, Italy, calls this 'a smart application of recent advances in the chemistry of nanoparticles to a very real analytical issue.' The next step for this sensor is to develop it into a more user friendly form, such as a test strip or reagent box that it can be used by the general public in their homes, say Han and Li. 

Rebecca Brodie 

Enjoy this story? Spread the word using the 'tools' menu on the left or add a comment to the Chemistry World blog.