Aggregation-induced emission enhancement of gold nanoclusters triggered by silicon nanoparticles for ratiometric detection of protamine and trypsin.

Metal nanoclusters protected by glutathione (GSH) have attracted a wide attention due to the unique aggregation-induced emission (AIE) feature. However, the "trigger" effects of ethanol, temperature, pH values, and metal ions may restrict the application of these particles. In this work, the amino modified silicon nanoparticles (SiNPs) and GSH-capped gold nanoclusters (GSH-AuNCs) can self-assemble into well-defined spherical particles due to the electrostatic interaction. As a result, the unique aggregation-induced emission enhancement (AIEE) of GSH-AuNCs arises at 570 nm, and the SiNPs keep their own blue fluorescence at 450 nm, so a novel nanohybrid probe (SiNPs@GSH-AuNCs) with dual-emission property has been constructed. When protamine is added to SiNPs@GSH-AuNCs, the cationic protamine can compete with SiNPs and absorb onto the surface of GSH-AuNCs, which inhibits the self-assembly and leads to the fluorescence quenching of GSH-AuNCs; while trypsin can catalyze the hydrolysis of protamine, the self-assembly starts again, producing the AIEE recovery. In the whole process, the SiNPs act as an internal standard and their emission stays constant. By means of the fluorescence intensity ratios I570/I450, the linear range of protamine is from 0.15 to 3.00 μg mL-1 with the limit of detection (LOD) of 0.07 μg mL-1, and trypsin shows a linear response in the range from 10 to 100 ng mL-1 with LOD of 4.50 ng mL-1. Furthermore, this strategy exhibits good sensitivity and selectivity, and has been further validated by applying it for the determination of protamine and trypsin in serum samples.