Novel rapid coordination of ascorbic acid 2-phosphate and iron(III) as chromogenic substrate system based on Fe2O3 nanoparticle and application in immunoassay for the colorimetric detection of carcinoembryonic antigen

This work for the first time reports on a simple and rapid colorimetric immunoassay with rapid coordination of ascorbic acid 2-phosphate (AAP) and iron (III) for determination of carcinoembryonic antigen (CEA, used as a model) by using Fe2O3 nanoparticle based-chromogenic substrate system. The signal was produced rapidly (1 min) from the coordination of AAP and iron (III) with color development of colorless to brown. TD-DFT calculation methods were employed to simulate the UV–Vis spectra of AAP-Fe2+ and AAP-Fe3+ complexes. Moreover, Fe2O3 nanoparticle could be dissolved with the aid of acid, thereby releasing free iron (III). Herein, a sandwich-type immunoassay was established based on Fe2O3 nanoparticle as labels. As target CEA concentration increased, the number of Fe2O3 labelled-antibodies (bound specifically) increased, resulting in loading more Fe2O3 nanoparticle on platform. The absorbance increased as the number of free iron (III), derived from Fe2O3 nanoparticle, increased. So, the absorbance of reaction solution is positively correlated with antigen concentration. Under optimal conditions, the current results showed good performance for CEA detection in the range 0.02–10.0 ng/mL with a detection limit of 11 pg/mL. Moreover, the repeatability, stability, and selectivity of the colorimetric immunoassay were also acceptable.