A label-free voltammetric immunoassay based on 3D-structured rGO–MWCNT–Pd for detection of human immunoglobulin G

• rGO–MWCNT–Pd nanocomposite has special 3D structure.
• Substrate materials rGO–MWCNT–Pd nanocomposite possesses excellent conductivity.
• Wide linear range and low detection limit.
• The immunosensor can detect HIgG in human serum.

In this work, a 3D-structured reduced graphene oxide–multiwalled carbon nanotube–palladium nanoparticles (NPs) nanocomposite (rGO–MWCNT–Pd) was prepared by a facile and green way and used as substrate material for the development of a label-free electrochemical immunoassay for human immunoglobulin G (HIgG) detection. The network structure of rGO–MWCNT nanocomposite provides more active sites for Pd nucleation. And the synergistic effect of rGO, MWCNTs and Pd NPs significantly improved the electrochemical performance of the modified electrode. Pd particles can combine HIgG antibodies and enhance the conductivity of electrode. The structure of rGO–MWCNT–Pd nanocomposite was characterized by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The HRTEM of Pd NPs and energy dispersive X-ray spectroscopy (EDS) of rGO–MWCNT–Pd nanocomposite confirmed the composition of the as-synthesized nanocomposite. K3[Fe(CN)6] was used as a redox probe. HIgG antibodies are immobilized onto the nanocomposite via PdNH2 bonds. Cyclic voltammetry and square wave voltammetry were used to characterize the recognizability of HIgG. Under optimum experimental conditions, the proposed immunoassay exhibited a low detection limit (3.3 pg/mL), a wide linear range (from 0.01 to 25 ng/mL) as well as good stability, reproducibility and selectivity.

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