An ultrasensitive immunochromatographic assay for non-pretreatment monitoring of chloramphenicol in raw milk

A non-pretreatment monitoring method based on immunochromatographic test (ICT) strips was developed to test for chloramphenicol (CAP) in raw milk. This assay was designed to measure competitive binding affinities for CAP molecules in raw milk and CAP antigen immobilized on strips with colloidal gold nanoparticles (GNPs, average diameter of 30 nm) labeled with anti-CAP monoclonal antibody (CAP mAb). Several working conditions, including the CAP solvent, different types and concentrations of CAP mAb, coating antigen, and GNP, were optimized for performance. After optimization, the detection process was carried out in 8 min with a visual limit of detection (LOD) of 0.3 ng/mL for qualitative detection and a LOD of 0.064 ng/mL for semi-quantitative detection. No cross-reactivity was detected toward CAP analogs. Based on these results, this simple and ultrasensitive assay could be thoroughly applied in the on-site testing of CAP in raw milk.