The development of a novel method for the purification of thrombin based on specific interaction with heparin, incorporated into polypyrrole (PPy) during growth, is described. Both platinised polyvinylidene fluoride (PVDF) membrane and reticulated vitreous carbon (RVC) were used as host substrates for the electrochemical deposition of polypyrrole-heparin. The heparin used was either unfractionated (Hep) or low-molecular-weight fractions with molecular weights of 3000 (HeP3000) or 6000 (Hep(6000)). A toluidine blue assay showed that using unfractionated heparin, a greater degree of excess sulfate groups existed in the biocomposite. However, thrombin binding was greatest for PPy-Hep(3000) and least for PPy-Hep. The use of applied potential (-0.3 V vs. Ag/AgCl (3 M MCl)) resulted in an increase in thrombin binding to the polymer, but reversing the potential failed to release the bound thrombin. Nevertheless, thrombin release was achieved by use of appropriate buffer or 4 M NaCl solutions. (C) 2002 Elsevier Science B.V. All rights reserved.