Development and application of a smartphone-based thermal contrast amplification reader for photothermal lateral flow immunoassays

The high cost and poor portability of external infrared thermal imagers have limited the widespread adoption of photothermal lateral flow immunoassays (PT-LFIAs) in on-site testing. To address this, we developed a smartphone-based handheld Thermal Contrast Amplification (TCA) Reader, eliminating the need for costly external hardware. Compared with existing recent external thermal imager-based PT-LFIA readout, this reader integrates a selected thermal-sensor-equipped smartphone, a motorized laser module, Bluetooth-enabled control, and a fixed 3D-printed holder into a compact device. The reader enables automated thermal signal acquisition with a same-strip measurement CV below 1% and supports multiple PT-LFIA formats. Using Au@Ag core-shell nanoparticles (Au@Ag NPs) as reliable photothermal labels, the handheld TCA reader-based PT-LFIAs (hT-PT-LFIAs) offers higher sensitivity compared to conventional LFIAs. The hT-PT-LFIAs can be used for the multiplex detection of viral antigens (Influenza A/B, SARS-CoV-2), small molecule drugs (morphine, methamphetamine, ketamine) and nucleic acids (HPV 16/18), demonstrating versatility across various LFIA formats, good clinical performance in training cohort, and high repeatability for small molecule assay. By seamlessly integrating micro-engineering, nanotechnology, and smartphone-based sensing, this work provides a low-cost, portable, and broadly applicable PT-LFIAs detection strategy that bridges a critical technological gap.