Label-free turn-on fluorescent detection of melamine based on the anti-quenching ability of Hg2+ to gold nanoclusters

• BSA-stabilized gold nanoclusters have been used for detecting melamine with a wide linear range and a low detection limit.
• The method is verified by detecting melamine in milk powder and raw milk with satisfactory recoveries.
• This method does not require any complicated modifications and expensive instrumentation.

In this work, we proposed a facile, environmentally friendly and cost-effective assay for melamine with BSA-stabilized gold nanoclusters (AuNCs) as a fluorescence reader. Melamine, which has a multi-nitrogen heterocyclic ring, is prone to coordinate with Hg2+. This property causes the anti-quenching ability of Hg2+ to AuNCs through decreasing the metallophilic interaction between Hg2+ and Au+. By this method, detection limit down to 0.15 µM is obtained, which is approximately 130 times lower than that of the US food and Drug Administration estimated melamine safety limit of 20 µM. Furthermore, several real samples spiked with melamine, including raw milk and milk powder, are analyzed using the sensing system with excellent recoveries. This gold-nanocluster-based fluorescent method could find applications in highly sensitive detection of melamine in real samples.