Copper nanoclusters with the properties of aggregation‐induced emission and peroxidase‐like activity simultaneously as a colorimetric nanoprobe for detecting captopril

In recent years, metal nanoclusters (M NCs) exhibiting either aggregation‐induced emission (AIE) or peroxidase‐like activity have attracted increasing research interest. However, M NCs that possess both AIE properties and peroxidase‐like activity remain rarely reported. In this study, copper nanoclusters stabilized by 3‐mercaptopropionic acid (Cu NCs‐MPA) were synthesized via a rapid aqueous‐phase method. As‐prepared Cu NCs‐MPA exhibited both AIE characteristics and peroxidase‐like activity. When dispersed in pure water, Cu NCs‐MPA displayed minimal fluorescence emission. However, bright orange fluorescence under 365 nm UV irradiation was observed when Cu NCs‐MPA were dispersed in mixtures of water and various organic solvents, including methanol (MeOH), ethanol (EtOH), ethylene glycol (EG), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). Notably, when Cu NCs‐MPA were dispersed in DMSO‐H2O mixtures, fluorescence intensity increased with higher DMSO content, confirming the distinct AIE behavior of Cu NCs‐MPA. Additionally, Cu NCs‐MPA exhibited significant peroxidase‐like catalytic activity in the H2O2–3,3′,5,5′‐tetramethylbenzidine (TMB) reaction system, effectively catalyzing the conversion of H2O2 into hydroxyl radicals (•OH), which subsequently oxidized TMB to blue‐colored oxidized TMB (oxTMB), resulting in increased ultraviolet absorbance at 652 nm. Upon addition of captopril, the •OH oxidized its thiol groups to form disulfide bonds (‐S‐S‐), thereby inhibiting oxTMB formation and reducing the absorbance at 652 nm. Based on this mechanism, a highly sensitive colorimetric assay was developed for captopril detection, with a linear range of 25–250 μM and a low detection limit of 3.93 μM. Moreover, the method was successfully applied to the determination of captopril in real pharmaceutical samples, demonstrating high sensitivity, good selectivity, and rapid response.