Ultrasensitive fluorescent detection of trypsin on the basis of surfactant–protamine assembly with tunable emission wavelength

Abstract

A facile and ultrasensitive fluorometric assay for trypsin detection was successfully established on the basis of surfactant/protamine/fluorescent hydrophobic dye assemblies. The supramolecular micellar-type assemblies were obtained by mixing the positively charged protein protamine as the substrate of trypsin with the anionic surfactant sodium dodecyl sulfate (SDS) at a level lower than its critical micelle concentration (CMC), and their apolar interiors could sequester several types of the representative hydrophobic fluorescent dyes such as Nile red, pyrene, and coumarin 6. It was found that the supramolecular assemblies exhibited a high specificity towards trypsin and its stability had a significant effect on the fluorescent intensity of the sequestered dyes. The addition of trypsin into the assembly system led to the dissociation of the assemblies and the decrease of the fluorescent intensity of the dye, which was exploited for trypsin detection and inhibitor screening. A detection level down to 0.044 ng mL⁻¹ was obtained for trypsin. Moreover, the emission wavelength and detection range could be tuned by simply varying the type of fluorescent dye.