Simultaneous electrochemical detection of Cd (II) and Pb (II) based on L-cysteine functionalized gold nanoparticles/metal-organic frameworks-graphene oxide nanocomposites

In this paper, a facile electrochemical sensor for simultaneous detection of Cd²⁺ and Pb²⁺ was fabricated, on the base of in situ growing gold nanoparticles (AuNPs) on L-cysteine functionalized metal-organic frameworks (L-MOFs) and graphene oxide (GO) nanocomposites (L-Au-MOFs-GO). First, L-MOFs were in-situ synthesized on the GO nanosheets by a one-step hydrothermal method. Then, the L-cysteine in L-MOFs-GO nanocomposite was used as a reductant to react with HAuCl₄ and in-situ obtain AuNPs, finally forming the L-Au-MOFs-GO composite. This L-Au-MOFs-GO composite not only can enhance the conductivity of the composite by accelerating the electron transfer, but also can act as an enrichment medium phase of heavy metal ions because of the interaction between metal cations and hydrophilic groups of L-MOFs or GO. The morphology of L-Au-MOFs-GO composites were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometer (FT-IR), and X-ray diffraction (XRD). The results showed that the electrochemical performance of L-Au-MOFs-GO composite was better than GO material or MOFs-GO composite. Under the optimal conditions, the L-Au-MOFs-GO modified electrode was successfully applied to individually and simultaneously detect the Cd²⁺ and Pb²⁺ in an acetic acid buffer solution with good selectivity and high sensitivity. This method was utilized for simultaneous detection of Cd²⁺ and Pb²⁺ in river water and the leaching solution of watermelon with great reliability and accuracy. This new nanomaterial for simultaneous detection of Cd²⁺ and Pb²⁺ has the potential application in complicated samples.