Colorimetric and photothermal dual-mode immunoassay for tumour marker detection based on a Ag2CO3@Ag nanocomposite

Under the limitations of advanced instruments and professional operations, straightforward readouts play an increasingly vital role in immunoassays. Herein, a Ag 2 CO 3 @Ag nanocomposite-mediated colorimetric and photothermal immunoassay was developed to detect carcinoembryonic antigen (CEA). The Ag 2 CO 3 @Ag nanocomposites could oxidize 3,3’,5,5’-tetramethylbenzidine to form blue oxidation products (TMB ox ) due to the acidic dissolution of Ag 2 CO 3 under acidic conditions. TMB ox presented a strong photothermal effect driven by a near-infrared (NIR) laser. Therefore, TMB ox could act as a photothermal probe to convert immunoassay signals into thermal signals. The Ag 2 CO 3 @Ag nanocomposite was characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD). Then, a sandwich-type immunoassay was built on the surface of a magnetic bead, and CEA was quantified using a common thermometer based on the photothermal effect. Under optimal conditions, the temperature increased with increase of CEA concentrations in the range of 0.1 ng/mL–5 ng/mL. More importantly, this system exhibited high selectivity, good repeatability and outstanding stability.