Ultrasensitive electrochemical immunoassay based on cadmium ion-functionalized PSA@PAA nanospheres

A simple strategy for sensitive detection of human IgG using cadmium ions-functionalized polymer nanospheres as the label is presented. The polymer nanosphere consisted of hard poly-styrene core and biocompatible poly (acrylic acid) (PAA) shell. The carboxyl groups of hydrophilic shell were used to chelated with the cadmium ions, and then conjugate with antibody (Ab(2)) to fabricate metal ions marked bioconjugates as the label in immunoassay. For constructing the matrix of the immunosensor, the PAA-functionalized carbon nanotubes were used to modify disposable screen printed electrodes for the immobilization of antibody (Ab(1)). After sandwich immunoreaction, differential pulse voltammetry was used to oxidize the conjuncted cadmium for the detection of antigen. The obtained results provided a linear response range from 0.1 to 35.0 pg/mL human IgG with a lower detection limit of 0.06 pg/mL, which is prominently improved in comparison with conventional immunoassay. The usage of the chelation reaction offers a simple and convenient route for the preparation of metallo-immunoassay labels, and also avoids the complicated and time-consuming dissolving of metal component for ultrasensitive determination. This approach is expected to have wide applications in protein diagnostics and bioanalysis in the future.