An ultrasensitive enzyme-free electrochemical immunosensor for CA125 using Au@Pd core-shell nanoparticles as labels...

A facile and sensitive enzyme-free sandwich-type immunosensor for the detection of carbohydrate antigen 125 (CA125) was designed based on Au@Pd core-shell nanoparticles. Au@Pd nanoparticles were used both as electrode-modifying materials to immobilize the primary antibody (Ab₁) of CA125 and as labels of secondary antibody (Ab₂). The covalent bond between palladium nanoparticles and available amine groups of Ab₁ enables the anchoring of larger amounts of Ab₁ while the high stability and bioactivity of Ab₁ can be reserved. Au@Pd nanoparticles show high electrocatalytic activity toward hydrogen peroxide (H₂O₂) reduction. The encapsulated Au nanoparticles can also accelerate the electron transfer. A high-performance electrochemical immunosensor was constructed based on the signal amplification of Au@Pd nanoparticles. Under optimal conditions, the immunosensor exhibited a wide linear response to CA125 ranging from 0.002 to 20 U mL^-1 with a low detection limit of 0.001 U mL^-1. The designed immunosensor displayed an excellent analytical performance with high sensitivity and stability. This strategy was successfully proved to be a simple method, which could be easily extended to other protein analysis.