We report a new type of potentiometric immunosensor for the determination of human a-fetoprotein (AFP). Gelatin-silver film as gentle carrier was used to immobilize anti-AFP on the surface of platinum disk electrode. The effective immobilization of the antibody comes from the entrapment by the gelatin film and graft by silver nanoparticles. Glutaraldehyde was employed to improve the character of complex film. Cyclic volatmmograms (CV) and electrochemical impedance spectroscopy (EIS) were used to determine the character of the film constituting the active phase of the electrode. The resulting AFP sensor exhibited a short response time (< 5 min), high sensitivity, low interference from other antigens, and a working lifetime at least 60 days. The analytical results by the proposed method were in satisfactory agreement with those by enzyme-linked immunosorbent assay (ELISA). It would be valuable for clinical immunoassay. (c) 2005 Elsevier Ltd. All rights reserved.