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/TiO 2 heterojunction nanomaterials . Firstly, chitosan modified AgI/TiO 2 photocatalyst (CS-AgI/TiO 2 ) 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/TiO 2 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.