Ultrasensitive non-mediator electrochemical immunosensors using Au/Ag/Au core/double shell nanoparticles as enzyme-mimetic labels.

Determination of squamous cell carcinoma antigen (SCCA) in human serum plays an important role in diagnosis of cervical squamous cell carcinoma. In this work, Au/Ag/Au core/double shell nanoparticles (Au/Ag/Au NPs) were prepared by a simple approach and were used as novel enzyme-mimetic labels for development of a sandwich-type electrochemical immunosensor for SCCA. The nanostructure of Au/Ag/Au NPs could be well confirmed by transmission electron microscope (TEM) and UV-vis spectra. Au NPs decorated mercapto-functionalized graphene sheets (Au@SH-GS) were used as platform for immobilization of primary antibody (Ab1), while Au/Ag/Au NPs were employed as labels of secondary antibody (Ab2). Due to the excellent electrocatalytic activity of Au/Ag/Au NPs towards the reduction of hydrogen peroxide (H2O2), electrochemical amperometric responses to SCCA were achieved after the immuno-reaction. Under optimum conditions, the electrochemical immunosensor exhibited a wide linear range from 0.5 pg/mL to 40 ng/mL with a low detection limit of 0.18 pg/mL for SCCA. The designed immunosensor displayed an excellent analytical performance with good reproducibility, high selectivity and stability.