Solid-contact electrochemical polyion sensors for monitoring peptidase activities

We report here on improved solid-contact electrochemical polyion sensors for the detection of polyion protamine. The polymeric membrane sensors were fabricated with a conducting polymer as an ion-electron transduction layer. We observed that decreasing the magnitude of the applied current pulse caused a significant improvement of the sensor sensitivity to low protamine levels. The protamine sensors exhibited a stable and reversible response to protamine concentrations ranging from 0.05 to 30 mg L-1. The sensors were used for monitoring peptidase activities utilizing galvanostatically controlled solid-contact membrane sensors. The polyion protamine was used as a substrate to detect the activity of the protease trypsin. The enzyme activity was continuously monitored by measuring the protamine concentration as it is cleaved by enzyme into smaller fragments to which the sensor is less sensitive. In the presence of a given level of protamine the initial rate of reaction can be linearly related to the trypsin activity within a 0-5 U mL-1 concentration range. The interference with the enzymatic reaction product arginine was specifically examined.