A novel microsphere-based fluorescence immunochromatographic assay for monitoring cefalexin residues in plasma, milk, muscle and liver

A novel, microsphere-based fluorescence immunochromatographic assay (MFIA), of higher sensitivity and faster detection than the monoclonal-based competitive indirect enzyme-linked immunosorbent assay (ci-ELISA), was developed for the routine surveillance of cefalexin antibiotic residues in plasma, milk, muscle and liver. The cross-reactivities of the fluorescent microsphere–monoclonal antibody (FM–mAb) conjugates to cefaclor, cefadroxil, cefradine and cefixime were 212.7%, 155.6%, 108.1% and 86.6%, respectively. The limits of detection of the proposed MFIA were <0.1 μg L−1 in all the cases, with IC50 values in the range from 0.59 to 0.71 μg L−1. The recoveries were 84.5% to 107.2% with the coefficient of variation less than 6.9% when cefalexin standards were spiked in selected biological matrices. Good correlations among the MFIA, ci-ELISA and ultra performance liquid chromatography-mass spectrometry/mass spectrometry (UPLC-MS/MS) results for blood samples from a cefalexin-injected rabbit were observed. In summary, the entire assay took about 30 min, and was simple, rapid, highly sensitive and cost-effective for both high-throughput screening and individual testing in food quality control.