Surface modification techniques and competitive immunoassay to detect residual ciprofloxacin in foods*

An easy and rapid method to detect ciprofloxacin residue, quinolone antibiotic, widely used on farm animals, was developed to ensure food safety. Antibody specific to ciprofloxacin was immobilised on surface-modified chips, and the microparticles and ciprofloxacin were conjugated covalently by two common cross-linkers. A linear correlation appeared between ciprofloxacin concentration and signal intensity at dynamic ranges of 0.1−10,000 μg/kg under the competitive binding format. The detection and quantification limits for standard solutions were 1 and 20 μg/kg, respectively. The recoveries and precision rates in real food matrices ranged from 48.7% to 59.2% and from 11.6% to 20.1%, respectively. The surface-modified microparticles and biochips enabled more sensitive detection of ciprofloxacin than currently available techniques, for screening. This novel method can enable simple and continuous detection in an inexpensive way, making it feasible to continuously monitor trace levels of antibiotics in large samples of food in a high-throughput manner.