Credit: © 2009 ACS

Melamine can cause renal failure in mammals but has been known to be illegally added to dairy products to falsify protein-content measurements based on the amount of nitrogen present. Current methods for detecting unsafe levels of melamine require expensive, complex instruments that make on-site detection difficult.

Now a team of chemists from the Changchun Institute of Applied Chemistry led by Lehui Lu have created1 a sensing system that has the potential for on-site and real-time detection of melamine in milk-based products. The aqueous sensing solution contains gold nanoparticles functionalized with a cyanuric acid (CA) derivative and changes colour on detection of melamine — from red to blue. Each melamine molecule forms a stable complex with up to three CA molecules, which causes the supramolecular aggregation of the functionalized nanoparticles, altering their optical properties.

The sensing system was able to detect 2.5 ppb of melamine in aqueous solutions through visually detectable colour changes and it was shown to be highly selective over similar molecules such as cytosine, uracil and thymine. The nanoparticles were also able to detect melamine impurities in tainted raw milk and infant formula, but in these cases the samples required a pre-treatment step prior to the measurements.