Design and implementation of a low-cost portable reader for thermometric lateral flow immunoassay

Lateral flow immunoassay (LFIA) is a widely used tool for point-of-care testing (POCT). Although the method is fast and inexpensive, it provides only qualitative or semi-quantitative information, which limits the scope of its applications in POCT. Here, we report the development of a low-cost, portable LFIA reader based on photothermal detection of reporters (such as colloidal gold and colored latex beads) captured on LFIA strips using a low-power green laser as the heating source and a single-element infrared sensor as the detector. For 40-nm colloidal gold, we measured a detection limit of 3 x 10(5) particles/mm(2) by laser irradiation of the reporters at 532 nm with an intensity of 20 W/cm(2). The photothermal detection enables a 10-fold enhancement in sensitivity over color visualization with the naked eye. More importantly, with the use of the control line intensities as internal calibrants, the results so obtained are quantitative and useful to support critical decision-making in POCT, as demonstrated by gold-based assays for human chorionic gonadotropin and human immunodeficiency virus as well as latex-based assays for nucleocapsid protein of the SARS-CoV-2 virus.