Spontaneous Growth of Au Nanoparticles onto CdS, ZnS or PbS Thin Films for Electrochemical Immunosensors

A facile method to fabricate Au-CdS (or ZnS, PbS) nanocomposites is reported. The method is based on spontaneous growth of Au onto the metal sulfide nanoparticles. Unlike typical synthesis of Au-semiconductor nanocomposites, this method does not require additional steps of introducing other reducing agents. Direct redox reactions occurs between Au(III) ions and metal sulfide nanoparticles. We have probed the Au-semiconductor nanocomposites by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). A possible mechanism was proposed for spontaneous growth of Au nanoparticles. It was found that H2O2 appeared to inhibit the Au growth onto the metal sulfide surface. We accordingly developed an enzyme-linked sandwich electrochemical immunosensor for the detection of human immunoglobulin G (IgG). In the electrochemical immunosensor, we use the glucose oxidase labeled antibody to generate H2O2 that inhibits the Au growth on CdS films, thereby decreasing the cathodic current at 0.9 V. This immunosensor can detect IgG as low as 1.5 ng/mL.