TiO2/SnOx-Au nanocomposite catalyzed photochromic reaction for colorimetric immunoassay of tumor marker

A simple colorimetric immunoassay based on visible light excitation for detection of carcinoembryonic antigen (CEA) was developed. Firstly, visible light photocatalysts of TiO 2 /SnO x -Au ternary heterostructures were prepared by in situ reduction method, which were characterized using transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD) and UV–vis diffuse reflectance spectroscopy (DRS). Then, a novel sandwich-type colorimetric immunoassay for quantitative analysis of CEA by using TiO 2 /SnO x -Au nanoparticle as signal tag was constructed. Under visible light irradiation (λ ≥ 420 nm), the color development of TMB was obtained. And the quantitative analysis was carried out in ABS buffer solution by ultraviolet spectrum scanning. Under optimal conditions, the absorbance values increased with the increasing of CEA levels in samples, which presented linear relationship in the range of 5 pg mL −1 –2.5 ng mL −1 with a detection limit of 5 pg mL -1 . Meanwhile, the colorimetric immunosensor owned acceptable specificity, stability and reproducibility.