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