Test detects trace melamine levels in milk products

Researchers have developed a new detector for melamine that could be used to identify tiny traces of the toxic chemical in milk.

Melamine adulteration of milk and infant formula has been a major concern since the notorious 2008 contamination scandal in China, in which more than 300,000 children suffered side effects from exposure to the chemical and up to 12 infants died.

Because of its high levels of nitrogen, melamine is added to milk and other food products such as eggs, biscuits, candy and coffee drinks to fool the standard Kjeldahl test, which provides a measure of protein levels.

Existing techniques to detect melamine in foods - including high performance liquid chromatography, gas chromatography coupled with mass spectrometry, voltammetry, infrared spectroscopy and Raman spectrometry - tend to be time consuming and labour-intensive whilst also requiring complex and often expensive equipment.  They also struggle to detect very concentrations.

The new detector - based on modified, fluorescent gold nanoparticles - can detect melamine levels down to femtomolar (fM) levels, well below the safe exposure limits (2.5mcg/L for adults and 1mcg/L for infants) set by the US Food and Drug Administration (FDA) in 2009.

Furthermore, it could serve as a simple, rapid, low-cost and portable screening method that is suitable for on-site detection, say the authors of the study, which is published in the journal Biosensors and Bioelectronics (April 15 edition).

The technique relies on the use of fluorescent gold nanoparticles capped with 3-amino-5-mercapto-1,2,4-triazole (AMTr) which give off purple emissions - measured by spectrofluorimetry - and gradually turn colourless as the concentration of melamine present increases.

The detection limit was the lowest of any test reported to date at just 10 fM/L, and the technique was robust even in the presence of 500-fold concentrations of potentially interfering elements such as sodium, potassium, calcium and chloride ions, cyanuric acid, glucose, sucrose, glycerol, alanine and ascorbic acid.