Novel signal amplification strategy for ultrasensitive sandwich-type electrochemical immunosensor employing Pd–Fe3O4-GS as the matrix and SiO2 as the label

An ultrasensitive sandwich-type electrochemical immunosensor based on a novel signal amplification strategy was developed for the quantitative determination of human immunoglobulin G (IgG). Pd nanocubes functionalized magnetic graphene sheet (Pd–Fe 3 O 4 -GS) was employed as the matrix to immobilize the primary antibodies (Ab 1 ). Owing to the synergetic effect between Pd nanocubes and magnetic graphene sheet (Fe 3 O 4 -GS), Pd–Fe 3 O 4 -GS can provide an obviously increasing electrochemical signal by electrochemical catalysis towards hydrogen peroxide (H 2 O 2 ). Silicon dioxide (SiO 2 ) was functionalized as the label to conjugate with the secondary antibodies (Ab 2 ). Due to the larger steric hindrance of the obtained conjugate (SiO 2 @Ab 2 ), the sensitive decrease of the electrochemical signal can be achieved after the specific recognition between antibodies and antigens. In this sense, this proposed immunosensor can achieve a high sensitivity, especially in the presence of low concentrations of IgG. Under optimum conditions, the proposed immunosensor offered an ultrasensitive and specific determination of IgG down to 3.2   fg/mL. This immunoassay method would open up a new promising platform to detect various tumor markers at ultralow levels for early diagnoses of different cancers.