Nanocomposites of nitrogen-doped graphene decorated with a palladium silver bimetallic alloy for use as a biosensor for methotrexate detection

Abstract

The synthesis and application of composites of N-graphene decorated with a bimetallic palladium–silver alloy (PdAg/NG–GCE) for the detection of methotrexate (MTX) are described. The nanocomposites were synthesized with different ratios of Ag and Pd (3 : 1, 1 : 1 and 2 : 1). Energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) show that the Pd and Ag cations were completely reduced to Pd and Ag, respectively, during the formation of PdAg/NG. Transmission electron microscopy (TEM) showed good loading between the PdAg alloy nanoparticles and the NG nanosheets with a Pd : Ag ratio of 1 : 1. The TEM results also depicted the existence of PdAg alloy nanoparticles with sizes between 3 and 13 nm, decorated on the surface of NG nanosheets. Electrochemical impedance spectroscopy (EIS) data also showed a decrease in the charge transfer resistance of Pd₁Ag₁/NG–GCE compared with Pd/NG, Ag/NG, NG and GCE, which suggests that the electron-transfer kinetics for MTX oxidation is highly facilitated at the Pd₁Ag₁/NG interface. The electrocatalytic activity of Pd₁Ag₁/NG–GCE towards MTX was also explored using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at pH 5.8. The anodic peak currents of MTX on Pd₁Ag₁/NG–GCE were approximately 8-fold higher than on the non-modified electrodes. A good linear ratio of the oxidation peak currents and MTX concentrations over the range of 0.02–200 μM with a limit of detection of 1.32 nM was achieved.