Computationally guided hapten design enables a colloidal gold immunochromatographic assay for rapid citalopram detection in water and dietary supplements

Citalopram, a widely prescribed selective serotonin reuptake inhibitor (SSRI), has emerged as an environmental and food contaminant owing to its extensive consumption and incomplete removal during wastewater treatment, posing potential risks to aquatic ecosystems and human health. Rapid on-site detection methods with high specificity are urgently required for routine monitoring, yet their development is largely constrained by the bottleneck in hapten design for high-performance antibody generation. Herein, a rational in silico strategy was applied to screen hapten candidates by systematically evaluating conformational similarity, charge distribution, physicochemical properties, and electrostatic potential, so as to maximally preserve the core epitope and molecular characteristics of citalopram. The optimal haptens were selected for animal immunization, and a high-specificity monoclonal antibody (mAb12H) was successfully obtained, with a half maximal inhibitory concentration (IC 50 ) of 0.88 ng/mL and no appreciable cross-reactivity observed toward 10 structural and functional analogs at the highest tested concentration of 1000 ng/mL. Molecular docking was further performed to elucidate the specific recognition mechanism, revealing that π-π stacking, hydrophobic microenvironment confinement, and auxiliary hydrogen bonding collectively dominate the stable and selective binding of citalopram. Based on this antibody, a colloidal gold immunochromatographic assay (CG-ICA) was established, achieving cut-off values of 5.0 ng/mL in environmental water and 40–45 ng/g in dietary supplements, with recoveries of 92.3%–108% and coefficients of variation of 3.44%–9.85%. This work provides a colloidal gold immunochromatographic assay for on-site citalopram screening, and also offers a practical paradigm for rational hapten design to improve specificity in small-molecule immunoassay development.