A Colorimetric Immunoassay Based on g-C(3)N(4)@Fe(3)O(4) Nanocomposite for Detection of Carcinoembryonic Antigen

We proposed a colorimetric immunosensor based on g-C(3)N(4)@Fe(3)O(4) nanocomposite-mediated transformation strategy for sensitive detection of carcinoembryonic antigen (CEA). The g-C(3)N(4)@Fe(3)O(4) nanocomposite was synthesized and characterized by the scanning electron microscope (SEM), energy dispersive X-ray spectra (EDX), X-ray powder diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Fe(3+) derived from g-C(3)N(4)@Fe(3)O(4) nanocomposite could combine with sodium salicylate to form purple complex products. Based on this color development, the sandwich colorimetric immunoassay was built by utilizing g-C(3)N(4)@Fe(3)O(4) nanocomposite as nanolabels on the microplate. With the increasement of CEA concentration, the purple color showed a gradient change. Under optimal conditions, the linearity range is 0.001–50 ng/mL with the detection limit of 0.35 pg/mL for CEA. More importantly, the colorimetric immunoassay has good selectivity, specificity, repeatability, and stability.