One-step synthesis of graphene oxide–thionine–Au nanocomposites and its application for electrochemical immunosensing

•Graphene oxide–thionine–Au nanocomposites was prepared by one-step approach.•GO–Thi–Au was used to fabricate electrochemical immunosensor.•The detection limit for CEA reached 0.05 fg mL−1 using this immunosensor.•This method performed very well on the detection of clinical serum specimens.

Here we report a one-step approach to synthesize graphene oxide–thionine–Au (GO–Thi–Au) nanocomposites using the synergistic effect of Thi and GO. Thi molecules adsorbed on the nanocomposites still kept the property of electroactive redox. Meanwhile, the resulting Au nanoparticles (AuNPs) of the nanocomposites offer active sites for the immobilization of biomolecules. The GO–Thi–Au nanocomposites are successfully employed for the fabrication of a simple, label-free, and ultrasensitive electrochemical immunosensor. Using carcinoembryonic antibody (anti-CEA) and carcinoembryonic antigen as model systems, the immunosensor showed an ultralow detection limit of 0.05 fg mL−1, and a linear calibration plot was obtained in a wide concentration range from 0.1 fg mL−1 to 1×109 fg mL−1.