Turn-On Near-Infrared Lateral Flow Immunoassay with Synergistic Energy Transfer for Direct and Ultrasensitive Detection in Complex Matrices.

The rapid, sensitive, and quantitative detection of small-molecule analytes in complex matrices remains fundamentally constrained by severe optical interference and limited signal transduction efficiency. Herein, we report a turn-on near-infrared (NIR) fluorescence lateral flow immunoassay (NFLFIA) that integrates indocyanine green-embedded nanoparticles and horseradish peroxidase-loaded gold nanorods as a spectrally matched donor-acceptor pair. Benefiting from the intrinsically low optical background of the NIR window and a cascade quenching mechanism governed by synergistic inner-filter effect and Förster resonance energy transfer, the NFLFIA enables ultrasensitive detection of aflatoxin M1 over an exceptionally broad dynamic range spanning 4 orders of magnitude, with a low limit of detection of 10.3 fg mL-1. With a sample-to-answer time of 30 min, this portable NIR-readout platform achieves sensitivity 3 orders of magnitude higher than commercial colloidal gold strips and delivers more reliable quantitative performance than 3-h-long enzyme-linked immunosorbent assays. This work establishes a robust and field-deployable platform for rapid, on-site monitoring of trace-level small molecules in complex matrices.