In 0.1 mol/l KH2PO4-Na2HPO4 (pH 7.80) buffer solution, the potential of zero charge (PZC) and the open circuit potential of gold-coated silicon were determined to be about -0.6 and +0.10 V (vs SCE), respectively. The open circuit potential was higher than the PZC, which indicated that the surface of the gold-coated electrode had a positive charge. The ellipsometry experiment showed that the adsorption of fibrinogen onto the gold-coated silicon wafer surface arrived at a saturated state when the adsorption time exceeded 50 min. The percentage of surface without adsorbed protein, theta, was about 63%. This means that the proportion of surface actually occupied by fibrinogen was only about 37% after the adsorption arrived at saturation. The solution/protein capacitance value was determined in an impulse state around -0.59 V (vs SCE) and was stable (4.2 x 10(-5) F) at other potentials. (C) 2003 Elsevier Inc. All rights reserved.