Trypsin is the most important digestive enzyme produced in the pancreas, and is a useful biomarker for pancreatitis. In this work, a rapid and sensitive method for the quantitative determination of trypsin activity is developed by using a biological alpha-hemolysin protein nanopore. Due to its much larger molecular diameter than the narrow pore constriction, trypsin itself cannot transport through the alpha-hemolysin channel. Hence, an indirect trypsin detection method is developed by monitoring its proteolytic cleavage of a lysine-containing peptide substrate. Based on the current modulations produced by the translocation of the substrate degradation products in the nanopore, the activity levels of trypsin could be determined. The method is rapid and highly sensitive, with picomolar concentrations of trypsin detected in minutes. In addition, the effects of cation and temperature on the sensor sensitivity, trypsin inhibition, and serum sample analysis are also investigated.

A label-free method for the measurement of the activity of HIV-1 protease is developed by real-time monitoring of the cleavage of a peptide substrate by HIV-1 protease in a nanopore. The method is rapid and sensitive: picomolar concentrations of HIV-1 protease could be detected in ~10 minutes. Simulated clinical samples are analyzed, and the activity of HIV-1 protease could be accurately detected. Our developed nanopore sensor design strategy should find useful application in the development of stochastic sensors for other proteases of medical, pharmaceutical, and biological importance.

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Scheme 1. Schematic illustration of a single nanopore sensor (left), typical single-channel recording trace segments (middle), and the constructed 3D plots of event counts versus residence time versus blockage amplitude for metal ion detection and differentiation (right). The ionic current through the nanopore is maintained by applying a voltage bias between two Ag/AgCl electrodes in an electrolyte solution.