Photoresponsive colorimetric immunoassay based on chitosan modified AgI/TiO2 heterojunction for highly sensitive chloramphenicol detection

Chloramphenicol (CAP) is an antibiotic used for a variety of infections, however, it is banned for use in food-producing animals due to its hazards to humans blood. Herein, the highly sensitive photoresponsive colorimetric immunoassay was exploited based on AgI/TiO2 heterojunction nanomaterials. Firstly, chitosan modified AgI/TiO2 photocatalyst (CS-AgI/TiO2) was synthesized by deposition-precipitation method, which was characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR). Then, by utilizing CS-AgI/TiO2 labeled CAP antibody as tags, a novel competitive-type immunoassay was constructed for detection of CAP on the surface of CAP-BSA modified magnetic bead. The color development of 3,3′,5,5′-tetramethylbenzidine (TMB) was obtained under visible light irradiation (λ≥420 nm) and the assay was carried out in pH 3.0 ABS buffer solution by UV-Vis spectrophotometry. Under optimal conditions, the absorbance values decreased with the increasing of CAP levels in sample, which exhibited linear in the range of 0.03-12.53 nM with a detection limit of 0.03 nM. Meanwhile, the selectivity, repeatability, and stability were acceptable. Excitedly, no significant difference was observed for detection of the spiked CAP in the real food samples with the referenced values.