Development of an ion-channel sensor for heparin detection

The ion-channel sensor technique was used to determine heparin concentrations in artificial and horse serum with cyclic voltammetry. The sensor is based on self-assembled monolayers (SAMs) of thioctic acid on which protamine is attached as a receptor to control the rate of [Mo(CN)8]4− oxidation or [Fe(CN)6]3− reduction in the presence of heparin. The analyte, heparin, with its negative charges, neutralizes the positive charges on the protamine receptor and at high heparin concentrations provides the electrode surface with an excess of negative charge, thereby repulsing the marker ions from the electrode surface. This decreases the redox currents and makes them a function of the analyte concentration. In artificial serum, a linear concentration range of 0.05–1.5 μg/ml was obtained for the heparin response at a scan rate of 10.24 V/s when [Mo(CN)8]4− was used as marker. Repeated measurements of heparin in artificial and horse serum gave average heparin concentrations of 1.30 and 1.56 μg/ml, respectively, compared to 1.25 μg/ml heparin that was introduced into the serum. Measurements of heparin in horse serum using a fresh electrode for each sample, however, gave an average heparin concentration of 1.21 μg/ml with a standard deviation of 0.026 μg/ml.