Colloidal Gold Immunochromatographic Assay for Rapid On-Site Detection of Tetracycline in Seawater

Recently increasing concerns from the scientists and public have been paid for seawater pollution due to tetracycline (TC) overuse in maricultural area. However, there are few methods or instruments that can be used for specific and rapid detection of this antibiotic in seawater. In this study, the colloidal gold immunochromatographic assay (CG-ICA) was used to achieve this goal. A commercialized monoclonal antibody against TC (anti-TC mAb) was selected because of its higher sensitivity (half-maximal inhibitory concentration of 2.38 µg L−1). The prepared CG particles (average diameter of 20 nm) were used to label anti-TC mAb at pH 8.0. The conjugate pad was formed by spraying the CG-labeled anti-TC mAb on a glass fibre membrane followed by proper dryness. The test pad was made by immobilizing artificial antigen and anti-mouse mAb in the test line and the control line, respectively, in a nitrocellulose membrane. The test strip, assembled with sample pad, conjugate pad, test pad and absorbent pad, could be used to detect TC during seawater sample flowing through these components in turn. The results could be observed by the naked eye in 10 min. The visible limit of detection (vLOD) was 20 µg L−1 for TC in seawater. The CG-ICA test results were in good agreement with those of liquid chromatography-tandem mass spectrometry (LC-MS/MS). The assay also showed that, oxytetracycline (OTC) and chlortetracycline (CTC), as the structural analogues of TC, did not interfere with TC determination. Furthermore, the TC concentration given by test strip could not be affected by the fluctuation of temperature (10°C–30°C), pH (7–9) and salinity (0–40) of seawater. Therefore, CG-ICA is a suitable tool for rapid, on-site, and semi-quantitative detection of TC in seawater.