Development of an ion-channel sensor for heparin detection

The ion-channel sensor technique was used to determine heparin concentratio ns in artificial and horse serum with cyclic voltammetry. The sensor is bas ed 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, hepar in, with its negative charges, neutralizes the positive charges on the prot amine receptor and at high heparin concentrations provides the electrode su rface with an excess of negative charge, thereby repulsing the marker ions from the electrode surface. This decreases the redox currents and makes the m a function of the analyte concentration. In artificial serum, a linear co ncentration range of 0.05-1.5 mu g/ml was obtained for the heparin response at a scan rate of 10.23 V/s when [Mo(CN)(8)](4-) was used as marker. Repea ted measurements of heparin in artificial and horse serum gave average hepa rin concentrations of 1.30 and 1.56 mu g/ml, respectively, compared to 1.25 mu g/ml heparin that was introduced into the serum. Measurements of hepari n in horse serum using a fresh electrode for each sample, however, gave an average heparin concentration of 1.21 mu g/ml with a standard deviation of 0.026 mu g/ml. (C) 2000 Elsevier Science B.V. All rights reserved.