Sandwich-type electrochemical immunosensor based on Au@Ag supported on functionalized phenolic resin microporous carbon spheres for ultrasensitive analysis of α-fetoprotein.

Signal amplification is crucial for obtaining low detection limits in electrochemical immunosensor. In this work, we developed a novel signal amplification strategy using Au@Ag nanoparticles loaded by polydopamine functionalized phenolic resin microporous carbon spheres (Au@Ag/PDA-PR-MCS). Phenolic resin microporous carbon spheres (PR-MCS) possesses uniform size and a large surface area (1656.8 m2 g-1). Polydopamine (PDA) functionalized phenolic resin microporous carbon spheres (PDA-PR-MCS) retains the advantages of PR-MCS and possesses strong adsorption ability. With the unique structure of PDA-PR-MCS, it not only improves the loading capacity and dispersity of Au@Ag nanoparticles (Au@Ag NPs), but also enhances the stability for the combination of the Au@Ag NPs by chemical absorption between Au@Ag NPs and -NH2 of PDA. The Au@Ag/PDA-PR-MCS exhibits extraordinary electrocatalytic activity towards reduction of hydrogen peroxide (H2O2) to make the electrochemical response more sensitive. Furthermore, Au NPs with good biocompatibility and excellent conductivity were electrodeposited on the surface of electrode, which was used as a sensing platform to immobilize primary antibody (Ab1) and accelerate the electron transfer on the electrode interface. Herein, the designed immunosensor provided a broad linear range from 20 fg/mL to 100 ng/mL for alpha fetoprotein (AFP) detection and a low detection limit of 6.7 fg/mL (signal-to-noise ratio of 3) under optimal experimental conditions. Moreover, the excellent performance in detection of human serum samples indicated that the proposed immunosensor will provide promising applications in clinical monitoring of AFP.