This quick and efficient detection method can render visual results, which can be confirmed by spectrophotometry.

Visual color and turbidity changes of gold nanoparticles resulted from different concentrations of melamine (decreasing from left to right). Source: Fang Wei, University of California, Los Angeles, and Na Li, University of Miami.
Melamine detection has required the use of expensive spectrophotometric equipment, and until melamine was first suspected in contaminated pet food and dairy products in 2007 and 2008 respectively, no procedures existed for finding its presence using lab equipment and software.

A new method of melamine detection, developed by University of Miami College of Engineering Assistant Professor Na Li and her colleagues, reveals the presence of melamine in a product visually in solution as the color turns from red to blue. Spectrophotometric equipment can also be used to verify the test, which takes seconds.

Li’s new method, which has been published in Applied Physics Letters, is entitled “Rapid Detection of Melamine in Whole Milk Mediated by Unmodified Gold Nanoparticles.” The study develops a facile and accurate approach to detection of melamine using gold nanoparticles and a dual-color precipitation test. The complete detection method can be performed in less than 15 minutes.

The fist step is to separate the casein-based milk component, which can interfere with melamine detection. Next, gold nanoparticles are added to the solution. The interaction between the gold nanoparticles and melamine causes a dramatic color change of the solution within seconds, from red to blue, indicating the presence of melamine. Melamine can be measured both by visual inspection and spectrophotometry.

“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 first author of the study.