Dual-mode colorimetric/photothermal lateral flow immunoassay using AuPd nanohybrids for sensitive detection of...

The presence of hormonal residues, such as progesterone (P₄) in food, whether due to illegal use or accumulation, raises serious food safety concerns, potentially disrupting endocrine function. There is an urgent need for rapid, sensitive, and matrix-tolerant screening methods. Herein, we report a dual-mode lateral flow immunoassay (LFIA) that combines colorimetric and photothermal detection for sensitive P₄ quantification, using gold-palladium (AuPd) nanohybrids as signal probes. The AuPd nanoprobes exhibit broad absorption across the visible to near-infrared spectrum and high photothermal conversion efficiency (41.30%), enhancing the detection signals in both modes. Under optimized conditions, the colorimetric (CLFIA) and photothermal (PLFIA) modes achieved detection limits of 0.263 ng/mL and 0.142 ng/mL, representing improvements of 2.7- and 3.2-fold over conventional AuNP-based assays. The method demonstrated good recovery rates (84.03%-106.61%) and reproducibility (RSDs <10%) in spiked milk and pork. This dual-mode LFIA is highly sensitive, user-friendly, and field-deployable, providing a robust tool for on-site screening of hormonal residues in complex food matrices.