Abstract: A regenerative capacitive immunosensor was proposed for direct detection of the complement Ⅲ(C₃) in human serum. Cysteamine selF^-assembled monolayers(SAM) firstly were combined on the gold electrode surface, and then a positively-charged chitosan monolayer was attached on the amine-modified SAM via the aid of glutaraldehyde cross-linking. To increase the insulation degree of the layer, the modified electrode was blocked with 1-dodecanethiol ethanol solution. Finally, the natural polysaccharide alginate, a negatively-charge polyelectrolyte, which was previously coupled with the anti-C₃ was adsorbed on the chitosan monolayer by strong electrostatic interaction to accomplish the immobilization of the anti-C₃. The dependence of chitosan/Au electrode stability on the pH and ion strength was studied with alternating current impedance. The immunosensor fabricated with proposed method can offer high sensitivity and easy regeneration after immunoassay through washing with basic solution without obvious decrease in response. The linear calibration curve is obtained with a detection limit of 9.1 ng/mL and a dynamic response range from 18.2 to 292.5 ng/mL when plotted vs. the logarithm of the antigen concentration. A recovery experiment demonstrates the feasibility of the proposed immunosensor for clinical diagnosis.

Key words: Electrostatic attraction, Capacitive immunosensor, Complement Ⅲ