Abstract: Apiezoelectric immunosensor has been developed for the determination of AFP.The crystal is AT-cut and has a basic resonant frequency of 9 MHz.Immobilization of theantibody of AFP(anti-AFP) to the crystal's surface is accomplished via a CNBr-activatedcopolymer coating of hydroxyethyl-methacrylate (HEMA )and methyl-methacrylate(MMA).The effects of immobilization method,the amount of copolymer coating and the reaction time between antigen and antibody are studied.Under the optimized conditions, the frequency shifts are linearly dependent on the AFPconcentrations in the range of 100~800ng/mL.Experimental results show that the piezoimmunosensor has good reproducibility, selectivity and sensitivity.Other antigens presented in human serum do not interfere with the sensor's response.Further, the valent value of AFPand anti-AFPand the affinity constant of immunoreaction in this experimental system are calculated.The analytical results given by this approach are in satisfactory agreement with those given by Radial Immunoassay(RIA).

Key words: Piezoelectric immunosensor, α-Fetoprotein, Copolymer of hydroxyethylmethacrylate and methyl-methacrylate, Affinity constant