We proposed a colorimetric immunosensor based on g-C₃N₄@Fe₃O₄ nanocomposite-mediated transformation strategy for sensitive detection of carcinoembryonic antigen (CEA). The g-C₃N₄@Fe₃O₄ 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). Fe³⁺ derived from g-C₃N₄@Fe₃O₄ 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-C₃N₄@Fe₃O₄ 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.

中文翻译：

---

基于 g-C3N4@Fe3O4 纳米复合材料的比色免疫法检测癌胚抗原

我们提出了一种基于gC ₃ N ₄ @Fe ₃ O ₄纳米复合材料介导的转化策略的比色免疫传感器，用于灵敏检测癌胚抗原（CEA）。合成了gC ₃ N ₄ @Fe ₃ O ₄纳米复合材料，并通过扫描电子显微镜（SEM）、能量色散X射线光谱（EDX）、X射线粉末衍射（XRD）和傅里叶变换红外光谱（FTIR）对其进行了表征。 ）。Fe ³⁺衍生自 gC ₃ N ₄ @Fe ₃ O ₄纳米复合材料可与水杨酸钠结合形成紫色络合物。基于这种显色，利用 gC ₃ N ₄ @Fe ₃ O ₄纳米复合材料作为微孔板上的纳米标记构建了夹心比色免疫测定法。随着CEA浓度的增加，紫色呈梯度变化。在最佳条件下，线性范围为 0.001–50 ng/mL，CEA 的检测限为 0.35 pg/mL。更重要的是，比色免疫测定具有良好的选择性、特异性、重复性和稳定性。