Sensor materials for the detection of proteases

The concept of generic and tunable sensor materials for the detection of proteases based on the thin film degradation of peptide cross-linked dextran hydrogels was explored. Hydrogel cross-links were formed via simple imine linkages between aldehyde groups in oxidized dextran and a peptide sequence susceptible to protease cleavage. Degradation of the hydrogel films was monitored in this study using a quartz crystal microbalance (QCM). The sensor material was developed using the protease/peptide pair of human neutrophil elastase (HNE) and Ala-Ala-Pro-Val-Ala-Ala-Lys (AAPVAAK). A direct relationship between the hydrogel degradation rate and protease activity was observed; HNE activities from 2.5 to 30 U ml−1 were detected using 25% cross-linked films. Film degradation was rapid and was complete in less than 10 min for HNE activities ≥10 U ml−1. An increase in the rate of degradation by a factor of 3.5 was achieved by increasing the cross-linking density from 25% to 75%. QCM admittance data fitted with a BVD equivalent circuit showed increases in film viscoelasticity upon enzyme addition. A second protease/peptide pair of cathepsin G and Ala-Ala-Pro-Phe-Phe-Lys (AAPFFK) was tested where 25% AAPFFK cross-linked hydrogels demonstrated a rapid response at 100 mU ml−1. Swapping the protease/peptide pairs to HNE/AAPFFK and cathepsin G/AAPVAAK showed low levels of cross-sensitivity further demonstrating the specificity of film degradation.