THE ISFET BASED HEPARIN SENSOR WITH A MONOLAYER OF PROTAMINE AS AFFINITY LIGAND

The ion-step measuring method was used to determine absolute heparin c oncentrations in PBS and blood plasma with a Ta2O5 ISFET on to which a monolayer of protamine had been immobilized. Heparin is a highly nega tively charged polysaccharide, which is used clinically to delay the c lotting of blood. Protamine acts as an affinity ligand for heparin. Th e response of the ISFET system on a step-wise increase in the electrol yte concentration (a so-called ion-step) is a transient change of the output voltage, which is related to the surface charge density of the ISFET gate oxide. After 2 mins of incubation in a plasma sample contai ning heparin, the amplitude of the transient ISFET response to an ion- step showed a linear relation to the heparin concentration. In blood p lasma, heparin concentrations between 0.3 and 2.0 Units/ml could be de termined with an accuracy of +/-0.08 Units/ml. Heparin concentrations in different plasma samples of heparinized patients were determined an d compared with the APTT. No direct relation was found between the APT T and the heparin concentration, but this result was not surprising.