The search for a rapid and effective test for melamine was made a priority following the contamination scandal in 2008, when tainted milk powder killed six children and sickened an estimated 300,000.
Writing in the peer-reviewed Talanta journal, researchers, funded by the Chinese Ministry of Health, said existing methods of detection offer a high degree of sensitivity but can be costly, time consuming and labour intensive.
In their search for a simpler alternative, they developed a colorimetric method using gold nanoparticles. The test relies on the fact that when gold nanoparticles approach each other and aggregate, their colour changes from wine red to purple (blue).
Because melamine kicks off this process, gold nanoparticles can be used as colorimetric probes to test for the toxin.
The proposed testing method can be used to test for melamine in liquid milk and infant formula with a detection limit of 1.0 ppm and 4.2 ppm respectively, relying on naked eye observation alone. And with UV-vis-spectroscopy, these limits can be improved to 0.15 ppm of melamine in liquid milk and 2.5 ppm in infant formula.
The test can be completed within 30 minutes and can be carried out without any need for pretreatment.
The study authors said: “The proposed method is promising for on-site screening of melamine adulterant in milk products.”
The scientists said their method offers obvious advantages such as a short analysis time and a low cost. In addition, it does not require any advanced instruments or solid phase extraction.
Although it is less sensitive than many other tests, the authors said it is sufficiently sensitive to detect melamine in milk-based products at levels desired by regulatory bodies.
In Europe and the US the safety limit for melamine has been set at 2.5mg kg−1 and in China the limit is set at 1mg kg−1 for infant formula and 2.5mg kg−1 for other dairy products.