DEVELOPMENT OF AN ISFET BASED HEPARIN SENSOR USING THE ION-STEP MEASURING METHOD

The ion-step measuring method was used to determine heparin concentrat ions in PBS and blood plasma. Heparin is a sulphated polysaccharide wh ich is clinically used as a drug to prevent the clotting of blood. The measuring method is based on detection of changes in charge density i n a porous membrane which is deposited on the gate of an ISFET. Protam ine was used as affinity ligand in the membrane. In PBS a linear relat ion was found between the heparin concentration and the ISFET response . The incubation time was reduced from 18 h to 15 min by increasing th e porosity of the membrane. The results of the measurements in blood p lasma show a significant nonspecific binding of plasma components in t he membrane. Suggestions are given to prevent this nonspecific adsorpt ion. The results described in this paper show a detection limit for th e ion-step measuring method of at least 5 +/- 10(-11) Mol/l which is p romising for future practical applications.