A fluorometric and colorimetric method for determination of trypsin by exploiting the gold nanocluster-induced aggregation of hemoglobin-coated gold nanoparticles.

A dual-signal assay is described for the determination of trypsin based on the use of gold nanoparticles (AuNPs) that aggregate in the presence of gold nanoclusters (AuNCs) due to electrostatic interaction. This is accompanied by a color change from red to blue. However, if hemoglobin (Hb) is present in the solution, it will attach to the surface of AuNPs, thus preventing aggregation. The Hb-coated AuNPs quench the fluorescence of AuNCs. Trypsin can hydrolyze Hb and destroy the protective coating of Hb on the AuNPs. As a result, AuNP aggregation will occur after the addition of AuNCs, and the blue fluorescence of the AuNCs with 365 nm excitation and 455 nm maximum emission peak is recovered. Thus, trypsin can be determined by measurement of fluorescence emission intensity. Additionally, trypsin can be determined by the maximum absorption peak wavelength between 530 nm and 610 nm. Fluorescence increases linearly in the 10-2500 ng⋅mL-1 concentration range, and absorbance in the 20-2000 ng·mL-1 concentration range. The limits of detection are 4.6 ng·mL-1 (fluorometry) and 8.4 ng·mL-1 (colorimetry), respectively. The assay is sensitive and selective, and can be applied to the determination of trypsin in serum. Graphical abstract Schematic presentation of a fluorometric and colorimetric method for determination of trypsin. The presence of hemoglobin (Hb) protects AuNPs from agglomeration after adding AuNCs and the fluorescence of AuNCs is quenched. With trypsin present, trypsin destroys the coating of AuNPs by Hb. AuNPs aggregate again and the fluorescence recovers after the addition of AuNCs.