Colorimetric-catalytic-fluorescence triple-mode lateral flow immunoassay based on Au@PtPd NPs for sensitive detection of capsaicinoids: Evaluation of edible oil and chili quality

Rapid quantification of capsaicinoids (CAPs) is critical for identifying recycled cooking oil and the grading of chili pepper pungency. In this study, a CAPs-specific monoclonal antibody and trimetallic core-shell Au@PtPd nanoparticles (Au@PtPd NPs) were prepared, the bare Au@PtPd NPs exhibited excellent antibody-binding capacity and pronounced fluorescence quenching effect. Notably, the as-prepared Au@PtPd NPs possess remarkable peroxidase-like activity (V_max = 0.389 μM/s, K_m = 0.834 mM), and after conjugation with the antibody (sAb-Au@PtPd), the catalytic activity was slightly enhanced (V_max = 0.403 μM/s, K_m = 0.832 mM). The multifunctional probe enabled the simultaneous generation of colorimetric, catalytic, and fluorescence signals. Based on this probe, a triple-signal lateral flow immunoassay (LFIA) was developed, overcoming the limitation of conventional single-signal qualitative detection. The three signals not only cross-validated each other but also achieved obvious signal amplification through catalytic and fluorescent readouts, substantially improving the sensitivity and accuracy of quantitative CAPs detection. The fluorescence mode exhibited the highest sensitivity, with a limit of detection (LOD) of 0.17 ng/mL and a linear range from 1.97 ng/mL to 3000 ng/mL - approximately 3.9-fold more sensitive than the colorimetric readout. The established LFIA enabled reliable and rapid CAPs detection in different matrices (edible oils and chili peppers), supporting on-site screening of recycled cooking oil and rapid pungency grading. This platform thus demonstrates substantial promise for food safety supervision and quality evaluation.