Electrostatic bridge-induced aggregation of silver nanoclusters for turn-on Mn2+ detection and luminescent film fabrication.

In this work, red-fluorescent silver nanoclusters (MMTA@Ag NCs) with aggregation-induced emission (AIE) properties were synthesized via a facile one-pot strategy at room temperature using 2-mercapto-4-methyl-5-thiazoleacetic acid (MMTA) as the capping ligand. The as-prepared Ag NCs initially exhibited weak fluorescence in aqueous solution with a quantum yield of only 0.0037. Upon the introduction of Mn2+, the metal ions acted as electrostatic bridges by coordinating with the carboxylate groups (-COO-) on the NCs surface, triggering significant aggregation of the nanoclusters. This aggregation effectively restricted intramolecular motion, leading to a remarkable "turn-on" fluorescence enhancement with a 100-fold increase in quantum yield to 0.38. Based on this AIE mechanism, a novel fluorescent sensing platform for Mn2+ detection was established. The method exhibited a satisfactory linear response over the Mn2+ concentration range of 0.01-0.50 µmol L-1 with a low detection limit of 9.79 nmol L-1 and excellent selectivity over other interfering ions. The proposed method was successfully applied to the determination of Mn2+ in milk samples, with satisfactory recoveries ranging from 99.0% to 106.2% and RSD below 2.7%. Furthermore, a highly luminescent PVA composite film was fabricated using the MMTA@Ag NCs-Mn2+ system, demonstrating promising potential in anti-counterfeiting applications.