Journal
MICROCHIMICA ACTA
Volume 183, Issue 1, Pages 441-448Publisher
SPRINGER WIEN
DOI: 10.1007/s00604-015-1669-3
Keywords
Oxidase mimetics; Tetramethylbenzidine; Colorimetric assay; Transmission electron microscopy; Photocatalysis
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Funding
- National Natural Science Foundation of China [21275065]
- Fundamental Research Funds for the Central Universities [JUSRP51314B]
- Opening Foundation of the State Key Laboratory of Analytical Chemistry for Life Science of Nanjing University [KLACLS1008]
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We describe a colorimetric assay for the quantitation of melamine (MA). It relies on the observation that MA reverses the inhibition of the light-triggered activity of horseradish peroxidase (HRP) functionalized gold nanoclusters (HRP-Au NCs) by Hg(II) ions. The HRP-Au NCs catalyze the oxidation of the substrate 3,3',5,5'-tetramethylbenzidine (TMB) by dissolved oxygen if exposed to visible light provided by a 300 W Xe lamp (lambda a parts per thousand yen 400 nm). The addition of Hg(II) suppresses the enzymatic activity due to the metallophilic interaction between Hg(II) and Au(I) present on the surface of the HRP-Au NCs. MA with its triazole ring can restore the catalytic activity of the HRP-Au NCs by inhibiting the metallophilic interaction. As a result of these findings, a colorimetric turn-on assay for MA was worked out that can be used to determine MA in the 0.2 to 15 mu mol center dot L-1 concentration range and with a 72 nmol center dot L-1 detection limit, which is much lower than the established safety limit. The method was successfully applied to the quantitation of MA in (spiked) raw milk and milk powder, with recoveries ranging from 98.5 % to 101.5 %.
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