Layer-by-layer assembly of chemical reduced graphene and carbon nanotubes for sensitive electrochemical immunoassay

In this work, uniform and stable multi-walled carbon nanotubes (MWCT) and chemically reduced graphene (GR) composite electrode interface was fabricated by using layer-by-layer assembly method. The performances of these GR-MWCT assembled electrode interfaces were studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). It was demonstrated that the assembled composite film significantly improved the interfacial electron transfer rate compared with that of GR or MWCT modified electrode. Based on the GR-MWCT assembled interface, a sandwich-type electrochemical immunosensor was constructed using human IgG as a model target. In this assay, human IgG was fixed as the target antigen, the HRP-conjugated IgG as the probing antibody and hydroquinone as the electron mediator. The detection limit of the immunosensor was 0.2 ng mL(-1) (signal-to-noise ratio of 3). A good linear relationship between the current signals and the concentrations of Human IgG was achieved from 1 ng mL(-1) to 500 ng mL(-1). Moreover, this electrochemical immunosensor exhibited excellent selectivity, stability and reproducibility, and can be used to accurately detect IgG concentration in human serum samples. The results suggest that the electrochemical immunosensor based on GR-MWCT assembled composite will be promising in the point-of-care diagnostics application of clinical screening of multiple diseases.