Aggregation-enhanced emission of metal nanoclusters triggered by peptide self-assembly and application in chymotrypsin inhibitor screening

Abstract Herein, a new strategy is developed to induce the aggregation of glutathione-capped gold nanoclusters (GSH-AuNCs) by self-assembly of peptide. The diphenylalanine peptide (L-Phe- l -Phe, FF) self-assembles in aqueous solution into the nano-net structure (FF-Nanonet, FF N). With self-assembly of FF, GSH-AuNCs aggregate in the network of FF N to form a dual-emission probe, called FF-N@GSH-AuNCs. One emission is from the self-assembled FF N at 470 nm, and the other one is the aggregation-induced enhanced emission (AIEE) of the GSH-AuNCs at 575 nm. Due to the hydrolysis of FF by chymotrypsin (CHT), the peptide bond on the carboxyl side of the phenylalanine is cleaved and the AIEE from GSH-AuNCs becomes faint because the released nanoclusters are dispersed in the solution again. Therefore, FF-N@GSH-AuNCs can be applied to screen and evaluate the CHT inhibitors. The inhibitory effects of four ingredients from natural products (i.e. epigallocatechin gallate (EGCG), tannic acid, oleanolic acid, and ursolic acid) on CHT activity have been studied. Oleanolic acid and ursolic acid are invalid. The half maximal inhibitory concentration (IC 50) values of EGCG and tannic acid are 13.9 and 19.2 μM, respectively. The screening results show that these two compounds have significant inhibitory effects on CHT.