An ultrasensitive fluorescent nanosensor for trypsin based on upconversion nanoparticles

Trypsin and its inhibitors are relevant to many physiological processes and diseases. In this study, a nanosensor capable of detecting trypsin and its inhibitors was designed based on the fluorescence resonance energy transfer (FRET) between upconversion nanoparticle (UCNP) and gold nanoparticle (AuNP). UCNP and AuNP were linked by a trypsin-sensitive peptide DDDDARC, forming the non-fluorescent UCNP-peptide-AuNP nanosensor. In the presence of trypsin, the peptide was cleaved and the quenched fluorescence was restored; in the presence of trypsin inhibitors, the recovery of the fluorescence was decreased. The nanosensor showed a superb sensitivity and selectivity for trypsin and its inhibitors, with a detection limit of 4.15 ng mL(-1) for trypsin. UCNP-peptide-AuNP could eliminate the interference of background fluorescence and avoid the light toxicity, and potentially be used to diagnose trypsin-related diseases or screen trypsin inhibitors.