A Sensitive and Specific Dual-T-Line Immunochromatographic Assay Based on Rational Hapten Design for On-Site Rapid Detection of Fenazaquin in Food and Environmental Samples

Fenazaquin (FEN), a widely used quinazoline acaricide, poses potential risks to public health and ecosystems due to its residue accumulation in food and the environment, thus demanding rapid and reliable detection methods. Herein, novel FEN haptens were rationally designed based on computational chemistry to successfully generate a highly specific and sensitive monoclonal antibody. The antibody exhibited a half-inhibitory concentration of 1.90 ng/mL. A gold nanoparticle-based dual-T-line lateral flow immunochromatographic assay was established for the rapid detection of FEN in lake water, soil, apples, and tea within 20 min. The detection limits were 1.74, 2.29, 4.38, and 2.64 μg/kg, with quantitative ranges of 6.12–450.44, 7.38–404.59, 11.49–309.78, and 8.16–385.02 μg/kg, respectively. Spiked recovery and blind sample tests showed excellent agreement with instrumental analysis. This study provides a rational hapten design strategy and a practical tool for field screening of FEN in food and environmental matrices.