Multicolor Biosensor for Trypsin Detection Based on the Regulation of the Peroxidase Activity of Bovine Serum Albumin-Coated Gold Nanoclusters and Etching of Gold Nanobipyramids

The detection of trypsin is significantly important for both clinical diagnosis and disease treatment. In this study, an innovative multicolor sensor for trypsin detection has been established based on the regulation of the peroxidase activity of bovine serum albumin-coated gold nanoclusters (BSA–Au NCs) and efficient etching of gold nanobipyramids (Au NBPs). BSA–Au NCs have slight peroxidase enzyme activity and can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to generate TMB+, while trypsin can hydrolyze BSA ligands on the surface of BSA–Au NCs, thus exposing more catalytic active sites of BSA–Au NCs and resulting in the enhancement of the peroxidase activity of BSA–Au NCs, hence more TMB+ is generated. Under acidic conditions, TMB+ can etch Au NBPs efficiently, consequently affecting the aspect ratio of Au NBPs accompanied by the ultraviolet–visible (UV–vis) spectra blue shifting of the system. Furthermore, this also results in color variations that can be distinguished and recognized by naked eyes without any expensive and sophisticated instruments. This multicolor sensor has an available linear relationship with the logarithm of the trypsin concentration in the range of 0.1–100 μg/mL, and the detection limit is 0.045 μg/mL. The designed sensor has been used to detect the concentration of trypsin in human serum samples from healthy individuals and pancreatitis patients with satisfactory results.