A ratiometric luminescence probe for selective detection of Ag based on thiolactic acid-capped gold nanoclusters with near-infrared emission and employing bovine serum albumin as a signal amplifier.

When thiolactic acid-capped gold nanoclusters (AuNCs@TLA) with strong near-infrared (NIR, 800 nm) emission were applied to detect metal ions, only Ag induced the generation of two new emission peaks at 610 and 670 nm in sequence and quenching the original NIR emission. The new peak at 670 nm generated after the 800-nm emission disappeared utterly. The ratiometric and turn-on responses showed different linear concentration ranges (0.10-4.0 μmol·L and 10-50 μmol·L) toward Ag, and the limit of detection (LOD) was 40 nmol·L. Especially, the probe exhibited extremely high selectivity and strong anti-interference from other metal ions. Mechanism studies showed that the novel responses were attributed to the anti-galvanic reaction of AuNCs to Ag and formation of bimetallic nanoclusters. The two new emission peaks were due to the composition change and size growth of the metal core. Besides, bovine serum albumin (BSA) has been employed as a signal amplifier based on the assembly-induced emission enhancement properties of AuNCs, which improved the LOD to 10 nmol·L. Moreover, the ratiometric method is feasible for Ag detection in diluted serum with high recovery rates, showing large application potential in the biological system. The present study supplies a novel ratiometric probe for Ag with a two-stage response and provides a novel signal amplifier of BSA, which will facilitate and promote the application of NIR-emitted metal nanoclusters in biological system.