Shark-Derived Single-Domain Antibody as a New and Effective Recognition Element for Norfloxacin Detection

ABSTRACT Low specificity and sensitivity often restrict the fluoroquinolones (FQs) detection when traditional IgG antibodies are used as recognition elements in immunoassay. Herein, shark-derived single-domain antibodies (ssdAbs) were used as new recognition elements to enhance the sensitivity and specificity for norfloxacin detection in immunoassay. Firstly, NOR-specific clones were isolated by phage display technology. Finally, five clones were successfully isolated from a NOR-immunized library. Secondly, a soluble expression system was constructed to produce ssdAbs. The 1N9 ssdAb exhibits the best affinity to the NOR complete antigen, with a limit of detection of 0.392   ng/mL and the cross-reaction rates of less than 8.240%, indicating its high sensitivity and specificity as a new recognition element in NOR detection. More importantly, the ELISA result proved that in NOR-negative fish matrix, no serious interference was observed, the 1N9 ssdAb could still recognize complete antigen NOR-OVA effectively. While in icELISA, 1N9 ssdAb could recognize NOR in different NOR-spiked concentrations between 10 to 1000   ng/mL, with the recovery rates between 93.66 - 116.49% with high reproducibility. Our study provides a new and effective recognition element with great potential for NOR detection.