De Novo Synthesis of Novel Haptens and Development of a Lateral Flow Immunochromatographic Sensor for the Detection of Aldicarb in Vegetables

Aldicarb is a highly toxic carbamate insecticide strictly regulated in vegetables, yet sensitive immunoassays remain limited because its small size and simple structure hinder the generation of high-performance antibodies. Two aldicarb haptens, Ald-262 and Ald-296, carrying an extended alkyl spacer and a benzene-containing spacer, respectively, at the carbamate terminus, were designed and synthesized by a total-synthesis route and characterized by mass spectrometry and density functional theory, which verified that the spacers preserve the epitope. Screening of homologous and heterologous hapten–carrier pairings showed that Ald-262 as an immunogen with Ald-296 as a coating antigen gave the best ic-ELISA response (IC50 = 11.94 ng/mL). Based on this antibody, a colloidal gold-based LFIA was developed, providing a detection range of 18.9–360.7 ng/mL, an IC50 of 82.5 ng/mL, and an estimate of the limit of detection (IC10) of 8.0 ng/mL. In spiked tomato and lettuce, it gave recoveries of 80.1–110.7% with coefficients of variation below 13.0% and correlated closely with UHPLC-MS/MS (y = 0.983x, R2 = 0.983). These findings demonstrate that rational modulation of hapten spacer architecture provides an effective strategy for antibody generation against structurally simple small-molecule pesticides and enables rapid on-site screening of aldicarb residues in vegetables.