Polyacrylamide hydrogel films cross-linked with the peptide sequence AAPVAAK were synthesised on piezoelectric quartz crystals. Degradation of the hydrogel films was monitored using a combination of quartz crystal microbalance (QCM) and electrochemical impedance measurements. The films were shown to degrade in the presence of human neutrophil elastase (HNE). The rate of degradation was directly related to the enzyme activity making the system suitable for the detection of HNE in the activity range from 0.72 to 30 U mL(-1). The films were not affected by non-specific adsorption. Film degradation was only accompanied by changes in the QCM signal, while no significant impedance change was observed during degradation. (C) 2009 Elsevier Ltd. All rights reserved.