An ultrasensitive electrochemical immunosensor for the detection of tumor marker human chorionic gonadotropin (hCG) was developed with a limit of detection as low as 2 pg ml-1 in phosphate buffer. The platinum nanoparticles (PtNPs) were electrodeposited to modify the gold surface and to increase enlarging the electrochemically active sites, resulting in the facilitation of electron exchange. Cysteamine (Cys) self-assembled monolayer was chemisorbed spontaneously on Pt substrates via the Pt-S bond and the amine groups array exposed on the electrode surface was used to anchor AgNPs through electrostatic interaction. AgNPs increased the immobilized amount of antibodies on the electrode to enhance the sensitivity of the sensor. Under optimal experimental parameters, differential pulse voltammetry (DPV) signal changes of the [Fe(CN)6]3-/4- are used to detect hCG with two broad linear ranges: 0.007-1.11 and 1.11-68 ng ml-1. The reported strategy has provided a promising platform for highly sensitive and selective detection of hCG. Finally, the proposed immunosensor is successfully used in detecting hCG in human serum samples.
