Electrochemical immunosensor for alpha-fetoprotein determination based on ZnSe quantum dots/Azure I/gold nanoparticles/poly (3,4-ethylenedioxythiophene) modified Pt electrode

A novel amperometric enzyme immunosensor with amplified sensitivity for the determination of alpha-fetoprotein (AFP) was constructed with layer-by-layer assembly of ZnSe quantum dots (ZnSe QDs)/Azure I/gold nanoparticles (nanoAu)/poly (3,4-ethylenedioxythiophene) (PEDOT) on Pt electrode. Firstly, citrate coated nanoAu was immobilized on the PEDOT polymer film, which was electrochemically synthesized in ionic liquid electrolyte of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]). Then, Azure I was immobilized on nanoAu/PEDOT composite matrix as a redox probe and was used to immobilize ZnSe QDs. Subsequently, AFP antibody (anti-AFP) was adsorbed onto the surface of ZnSe layer. Finally, horseradish peroxidase (HRP) was employed to block sites against nonspecific binding and amplify the current signal of the antigen–antibody reaction. The modification processes were characterized by cyclic voltammetry, scanning electron microscopy. The factors influenced the performances of the proposed immunosensors were studied in detail. Because of the synergism between Azure I and nanoAu/PEDOT to facilitate electron-transfer process, and the small diameter of ZnSe QDs favorable for stabilization of biological activity to a large extent, the immunosensor displayed a high sensitivity, fast analytical time, a relatively low detection limit of 1.1 fg/mL at 3 times of signal-to-noise ratio (S/N = 3), and a especially broad linear response to AFP in a ranges from 5 × 10−5 to 250 ng/mL. Moreover, the selectivity, repeatability, and stability of the proposed immunosensor were acceptable.