A Pocket Test For Melamine-Adulterated Milk | Chemical & Engineering News
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Web Date: July 20, 2015

A Pocket Test For Melamine-Adulterated Milk

Analytical Chemistry: Chemists adapt the personal glucose meter to test for illegal milk additive
Department: Science & Technology | Collection: Entrepreneurs, Life Sciences
News Channels: Analytical SCENE, Biological SCENE
Keywords: melamine, personal glucose meter, aptamer, kidney, milk, infant, invertase
Scientists have developed a test that detects melamine (left) in milk using a glucose meter (right).
Credit: Shutterstock

A new test converts the personal glucose meter (PGM) into a portable tool for exposing milk contaminated with melamine (Anal. Chem. 2015, DOI: 10.1021/acs.analchem.5b01085).

Used in plastic dinnerware, colorants, and flame retardants, melamine is not approved for use in food. Yet, in 2008, the Chinese government discovered that manufacturers were illegally adding melamine to milk powder, a practice that led to six infant deaths that year and sickened 300,000, according to news reports. Melamine’s high nitrogen content fools simple tests for protein, indicating falsely high protein levels. Subsequently, both U.S. and Chinese governments imposed a limit of 1-ppm melamine in infant milk products.

A fast, portable test that could check for melamine adulteration anywhere along the chain of production would help manufacturers and consumers, says Yi Lu of the University of Illinois, Urbana-Champaign. Lu’s group has developed ways to use the PGM to determine concentrations of metal ions, antibodies, and more. Lu and collaborators at Tsinghua University, in Beijing, extended this to melamine in milk.

The researchers identified a DNA aptamer—a sequence that binds with high specificity to a molecule of interest—for melamine. To measure melamine concentrations, the researchers add the aptamer to milk along with two complementary DNA sequences: one linked to a magnetic bead and the other to invertase enzyme, which converts sucrose to glucose. In the absence of melamine, the aptamer binds to both the bead and to invertase, allowing the researchers to remove invertase from the solution with a magnet. But if the aptamer binds melamine, it can’t bind to the bead or to invertase. The magnet removes empty beads, leaving behind invertase in proportion to the melamine concentration. Then when the researchers mix the sample with sucrose, the invertase produces glucose for the PGM to measure. The aptamer can detect melamine at 67.5 ppb in the presence of melamine analogs and milk proteins.

GlucoSentient, a company Lu cofounded, is working to commercialize the test.

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Dan Bode (Wed Jul 22 14:37:39 EDT 2015)
A fascinating use of the technology, but it raises a question. Melamine is approved as an ingredient in the formation of melamine formaledehyde crosslinkers for food contact use in coatings and articles [plastic dinnerware, as stated]. This device may detect melamine from approved uses at levels that would not pose a health risk, giving a false positive for adulteration.
Frankie Wood-Black (Sat Jul 25 11:32:38 EDT 2015)
Remember that dipstick technology was one of Helen Free's inventions!

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