Cation-driven luminescent self-assembled dots of copper nanoclusters with aggregation-induced emission for β-galactosidase activity monitoring

Thiolate-protected copper nanoclusters (CuNCs) with aggregation-induced emission (AIE) have emerged as a novel kind of luminescent material, but their applications in neutral solution are greatly limited by their ultra-low emission efficiency under such conditions. Herein, we report a facile synthesis of glutathione-protected CuNCs with AIE properties, and their self-assembly was driven by aluminum cations. The bright red luminescence of solid CuNCs illustrates their significant AIE nature, but CuNCs dispersed in neutral water exhibit almost no luminescence. It was found that aluminum cations were capable of driving the self-assembly of the CuNCs, and the resulting CuNC dots with controllable sizes retain their bright luminescence under neutral conditions. The strong affinity of GSH ligands to the CuNCs contributes to this good stability in neutral and even in weakly alkaline solutions. The stable existence of the luminescent CuNC dots enables them to function as a luminogen under physiological conditions. This ability was employed to detect beta-galactosidase activity using 4-nitrophenyl-beta-D-galactopyranoside as the substrate. The strong quenching effect of the CuNC dots by p-nitrophenol was used to achieve a sensitive measurement of the beta-Gal level. This work proposes the preparation of CuNC dots with bright luminescence in neutral solution via the self-assembly of GSH-capped CuNCs by aluminum ions, and demonstrates their sensing application in the detection of beta-galactosidase activity under physiological conditions.