Colour changing nanoparticles to flag up melamine-tainted milk
A research team from the University of Miami has developed the test using gold nanoparticles which change colour in the presence of melamine. The process, which also involves a dual colour and precipitation test, takes only 15 minutes, said assistant professor Na Li.
"Current methods of melamine detection in milk are costly and time consuming," she added. "Our work represents a significant step towards the rapid detection of melamine, which addresses a critical global issue."
Detection of melamine in milk became of worldwide concern in the wake of the 2008 contamination crisis when thousands of tonnes of the chemical were added to milk powder by Chinese manufacturers. Some 300,000 people were sickened and six died as a result of the scandal.
Test method
The new process first involves the separation of the casein-based component in the milk, as this can interfere with melamine detection, before the nanoparticles are added to the solution. The team said the interaction between the gold nanoparticles and melamine causes a dramatic colour change in tainted milk.
“When melamine is present, the colour of the solution changes from red to blue within seconds and can be measured both by visual inspection and spectrophotometry,” said the team.
Specificity can be increased by the sequential introduction of cyanuric acid – which is employed because it has a specific reaction with melamine. If melamine is present, a precipitant is formed, which can also be assessed both visually and by spectrophotometry, said the paper published in in the online journal Applied Physics Letters.
Dean Ho, assistant professor in the Departments of Biomedical and Mechanical Engineering, said: “It's important to utilize nanoparticles that can be manufactured in high yield, which makes it possible to have a method that can be widely used."
The team said it hoped to bring a simplified kit to market that could be used by the layperson, at home or in the field, to detect melamine in food.
"Our method provides not only an alternative method to the current lab-based detection, but also a way for early screening of milk, especially for field work and for developing countries," says Fang Wei, staff research associate in the Department of Mechanical and Aerospace Engineering, at the University of California, Los Angeles and study lead author.
'Rapid Detection of Melamine in Whole Milk Mediated by Unmodified Gold Nanoparticles', by Fang Wei, Robert Lam, Stacy Cheng, Steven Lu, Dean Ho and Na Li is published in Applied Physics Letters.
