Gold/WS.sub.2 nanocomposites fabricated by in-situ ultrasonication and assembling for photoelectrochemical immunosensing of carcinoembryonic antigen

Tungsten disulfide (WS.sub.2) nanosheets were obtained by exfoliating WS.sub.2 bulk crystals in N-methylpyrrolidone by ultrasonication. Gold nanoparticles (GNPs) were synthesized by in-situ ultrasonication of sodium citrate and HAuCl.sub.4 while fabricating the WS.sub.2 nanosheets. In this way, the GNPs were self-assembled on WS.sub.2 nanosheets to form a GNPs/WS.sub.2 nanocomposite through interaction between sulfur and gold atoms. The photoelectrochemical response of WS.sub.2 nanosheets is significantly enhanced after integration of the GNPs. The GNPs/WS.sub.2 nanocomposite was coated onto a glassy carbon electrode (GCE) to construct a sensing interface which then was modified with an antibody against the carcinoembryonic antigen (CEA) to obtain a photoelectrochemical immunosensor for CEA. Under optimized conditions, the decline in relative photocurrent is linearly related to the logarithm of the CEA concentration in the range from 0.001 to 40 ng mL.sup.-1. The detection limit is 0.5 pg mL.sup.-1 (at S/N = 3). The assay is sensitive, selective, stable and reproducible. It was applied to the determination of CEA in clinical serum samples.