Synthesis and electrocatalytic effect of Ag@Pt core-shell nanoparticles supported on reduced graphene oxide for sensitive and simple label-free electrochemical aptasensor

Bimetallic Ag@Pt core-shell nanoparticles supported on reduced graphene oxide nanosheets (Ag@Pt-GRs) was synthesized and used as novel desirable sensor platform and electrocatalyst for catechol as probe in aptasensor. Gold screen-printed electrodes modified with Ag@Pt-GRs and applied to advance enzyme-free and label-free electrochemical aptasensor for detection of protein biomarker tumor necrosis factor-alpha (TNF-alpha). The morphology of the Ag@Pt-GRs could be characterized by transmission electron microscopy, X-ray diffraction and UV-vis spectra. The results showed that these nanocomposite exhibited attractive electrocatalytic activity and also yielded large surface area, which improve the amount of immobilized TNF-alpha aptamer. Due to the excellent electrocatalytic activity of Ag@Pt-GRs towards the oxidation of catechol, determination of TNF-alpha antigen was based on its obstruction to the electrocatalytic oxidation of catechol by Ag@Pt-GRs after binding to the surface of electrode through interaction with the aptamer. The calibration curve was obtained by differential pulse voltammetry and square wave voltammetry. Under optimum conditions, the results demonstrated that this electrochemical aptasensor possessed a dynamic range from 0.0 pg/mL to 60 pg/mL with a low detection limit of 2.07 pg/mL for TNF-alpha. The analytical usefulness of the aptasensor was finally demonstrated analyzing serum samples. The simple fabrication method, high sensitivity, specificity, good reproducibility and stability as well as acceptable accuracy for TNF-alpha detection in human serum samples are the main advantages of this aptasensor, which might have broad applications in protein diagnostics and bioassay. (C) 2015 Elsevier B.V. All rights reserved.