Turn-on fluorescent detection of melamine based on Ag nanoclusters–Hg2+ system

An efficient sensor was developed for highly sensitive and selective determination of melamine based on Ag nanoclusters (Ag NCs) capped by hyperbranched polyethyleneimine (PEI) molecules with different molecular weights. The fluorescence of the Ag NCs could be quenched by Hg2+ and recovered by melamine. The molecular weights of PEI had an appreciable effect on the sensitivity, and Ag NCs capped by PEI with a molecular weight of 600 were more sensitive; the linear range of melamine was from 0.1 to 30 μM with a detection limit 30 nM. Moreover, this Ag NCs–Hg2+ system displayed excellent selectivity over common interferences such as metal ions, amino acids, sugars and nitrogen-containing organic molecules. Benefiting from the high selectivity, good recoveries ranging from 96% to 101% were obtained in food samples, including milk, infant formula, and dog food. More importantly, Ag NC-doped agarose hydrogels were fabricated easily to construct a visual device for the detection of melamine in food samples.