Determination of trypsin using protamine mediated fluorescent enhancement of DNA templated Au nanoclusters

A fluorescent method is described for trypsin determination through the strong electrostatic interactions between cationic polyelectrolytes and single-stranded DNA (ssDNA) templated Au nanoclusters (AuNCs). The ssDNA-AuNCs display improved fluorescence emission with excitation/emission maxima at 280/475 nm after being incorporated with poly(diallyldimethylammonium chloride) (PDDA). Fluorescent enhancement is mainly attributed to the electrostatic interactions occurring between PDDA and ssDNA templates. This can make the conformation of the ssDNA templates to change. Thus, it offers a better microenvironment for stabilizing and protecting ssDNA-AuNCs, and results in fluorescence emission enhancement. By using protamine as a model, the method is employed for the determination of trypsin. The assay enables trypsin to be determined with good sensitivity and a linear response ranging from 5 ng center dot mL(-1) to 60 ng center dot mL(-1) with a 1.5 ng center dot mL(-1) limit of detection. It is also extended to determine the trypsin contents in human's serum samples with recoveries between 98.7% and 103.5% with relative standard deviations (RSDs) between 3.5% and 4.8%.

Automated summary

A fluorescent method utilizing the electrostatic interactions between cationic polyelectrolytes and ssDNA templated AuNCs is developed for trypsin determination. The incorporation of PDDA improves the fluorescence emission of ssDNA-AuNCs with excitation/emission maxima at 280/475 nm. The method shows good sensitivity and a linear response range of 5-60 ng·mL(-1) with a detection limit of 1.5 ng·mL(-1) for trypsin determination.