Detecting melamine in milk has become extremely easy, quick and inexpensive thanks to a handheld melamine detector developed by researchers at the Indian Institute of Science (IISc), Bangalore. Leaf extract of a commonly seen weed parthenium along with silver nitrate is used for detecting the presence of melamine in milk. The results were published in the journal Sensors and Actuators B: Chemical.
“The presence of melamine in milk can be detected at room temperature within a few seconds through a change in colour,” says S.C.G. Kiruba Daniel from the Department of Instrumentation and Applied Physics, IISc and the first author of the paper.
“Our sensor has a very high sensitivity as it can detect melamine even at a low concentration of 0.5 ppm in raw milk.” Melamine content of more than 1 ppm in infant formula and more than 2.5 ppm in other foods should be viewed with suspicion of adulteration, says the Food Safety and Standards Authority of India.
In 2008, at least four babies in China died and around 100,000 became sick after consuming powdered milk baby food laced with melamine. Due to the presence of nitrogen, the addition of melamine to milk makes it look protein-rich.
Prior to melamine detection, the milk is processed to remove fat and proteins as they tend to interfere with detection. While most researchers had used already prepared silver nanoparticles for melamine detection, the IISc team added silver nitrate and the leaf extract in a particular ratio and at a particular pH to the preprocessed milk to synthesise silver nanoparticles.
“If melamine is present then it interferes with the synthesis and there is abrupt formation of nanoparticles leading to colour change,” says Dr. Daniel.
The change in colour depends on the amount of melamine present and, therefore, the extent of its interference with the synthesis of silver nanoparticles. “The colour change can be directly observed by the naked eye and also recorded by spectral change,” he says.
The silver nanoparticles are reddish yellow in the absence of melamine, while it becomes nearly colourless when melamine is present. Light absorption at 414 nm wavelength is a signature of silver nanopartciles. But when melamine is present the absorption of light is reduced as nanoparticle formation decreases.
“Currently, milk samples have to be brought to a central testing facility, so very less testing gets done. But all this can change with our handheld device,” Dr. Daniel says. As little as 1 ml of milk is sufficient for carrying out melamine detection.
The team is in the process of commercialising the product through a start-up that is incubated at the Society for Innovation & Development Centre at IISc.