Abstract: Objective: To establish a nano-gold capillary immunochromatographic assay (CICA) based on a combination of colloidal-gold labeling and Immunochromatography for the rapid field detection of enrofloxacin (EF) residues in aquatic products. Methods: Based on the principle of indirect competitive immunoreaction, the CICA method was developed by optimizing antigen concentration in the test area, secondary antibody in the control area and gold-labeled antibody standard concentration. Then the sensitivity, specificity and repeatability of this method and several sample pretreatments were evaluated. Results: The visual and semi-quantitative detection limits for EF were estimated to be 5 and 1.29 ng/mL, respectively. The recoveries of EF in spiked negative samples of turbot, Spanish mackerel, tonguefishes, and Pacific while shrimp (P. vannamei) were 78.3%–129% and The intra- and inter-assay precision expressed as relative standard deviation (RSD) was less than 10%. Specificity analysis indicated that this method had strong specificity to all analogues except ciprofloxacin (CIP), for which the visual and semi-quantitative detection limit were 10 and 4.37 ng/mL, respectively and met the requirement of the national standard of China. Sulfonic acid extraction under normal temperature conditions was chosen as the optimal pretreatment method for CICA. Conclusion: CICA was a simple, rapid, easy-to-operate and reproducible method and could provide a new approach for the detection of antibiotic residues in aquatic products. Meanwhile, the pretreatment method for CICA chosen in this study can provide a theoretical basis and technical support for other rapid detection methods.

Key words: enrofloxacin, immunochromatography, capillary, colloidal gold