Improving mycotoxin enzyme immunoassay performance by optimizing formaldehyde-mediated hapten–protein conjugation: an α-cyclopiazonic acid case study

Enzyme immunoassays (EIAs) for small molecules often suffer from limited sensitivity or high non-specific background. This study presents a reproducible strategy to improve EIA performance by optimizing hapten-protein conjugation conditions. Using an immunoassay for the mycotoxin α-cyclopiazonic acid (α-CPA) as a case study, key parameters of the formaldehyde-mediated (Mannich) condensation reaction for synthesizing a hapten-bovine serum albumin conjugate were systematically investigated. Variation of reaction temperature (8-37°C) and time (0.25-72 h) showed that short reaction times at low temperature markedly improved assay performance. Under optimized conditions (8°C, 15 min), the detection limit improved from >100 ng/mL to 2.4 ± 0.2 ng/mL, with a strong reduction in non-specific background. The results demonstrate that targeted optimization of hapten-protein conjugation can significantly enhance EIA sensitivity and specificity, which helps to reduce the number of laboratory animals for antibody production. The approach is readily transferable to other indole-containing mycotoxins and was successfully applied to determine α-CPA in fungal agar plugs from mold-ripened cheeses. This study highlights an important aspect of conjugation conditions during immunoassay optimization. •Systematic optimization of formaldehyde-mediated hapten-protein conjugation for EIAs •Improved assay sensitivity and background without new antibody production •Transferable strategy demonstrated for α-CPA analysis in complex fungal samples.