doi:10.1038/nindia.2013.25 Published online 19 February 2013
Researchers have designed a new kind of sensor using modified, fluorescent gold nanoparticles that can detect extremely low concentrations of melamine, a nitrogen-rich organic compound used to adulterate milk, infant formula and various other foodstuffs1. The sensor will be useful in identifying food products contaminated with melamine.
Melamine-contaminated milk is known to have deleterious effects on children's kidneys. Animal studies suggest that melamine-containing foods could trigger bladder cancer. Existing techniques to detect melamine in foods are selective and fail to track minute traces.
To devise a better melamine sensor, the researchers synthesized fluorescent gold nanoparticles using amino-mercapto-triazole, an organic compound. The nanoparticles were capped with the organic compound. They then used these nanoparticles to identify traces of melamine in real samples such as cow milk and infant formula.
They prepared several samples with varying concentrations of melamine and added them to solutions of fluorescent nanoparticles. Increasing the melamine concentrations from femtomolar to picomolar levels increased the emissions, turning the wine-red nanoparticles-containing solutions to purple. The nanoparticles-containing solution turned colourless when melamine was added at micromolar concentrations.
The study showed that the nanoparticles could selectively detect traces of melamine even in the presence of 500-fold concentrations of common interfering agents such as sodium, potassium, calcium and chloride ions, cyanuric acid, glucose, sucrose, glycerol, alanine and ascorbic acid.
"In future, this sensor might be used to quantitatively determine the presence of melamine in dairy products," says lead researcher S. Abraham John.