Near-infrared induced photothermal lateral-flow immunoassay utilizing plasmonics-active gold nanostars.

The lateral flow immunoassay (LFIA) has become a widely accepted point-of-care diagnostic tool (POCT) due to its simplicity, portability, cost-effectiveness, and rapid biomarker detection capabilities. However, its sensitivity in detecting target analytes has been limited by the visual signals produced by traditional gold nanoparticles. In this study, we introduce a highly sensitive near infrared (NIR) photothermal platform using gold nanostars (GNS) with a tunable plasmon resonance band spanning wavelengths from 700 to 850 nm. The GNS, particularly the GNS-3 probe with its large number of branches, exhibited exceptional light-to-heat conversion efficiency, significantly enhancing photothermal conversion. Using GNS-3 as an efficient photothermal probe, we successfully detected the high-risk pathogen Francisella Tularensis biomarker lipopolysaccharide (FtLPS) as the model analyte, achieving an outstanding limit of detection (LOD) of 3.5 pg/mL for photothermal LFIA. This photothermal LFIA enhances the detection sensitivity nearly 1000-fold compared to traditional colorimetric gold nanosphere-based LFIA. Furthermore, we demonstrate the potential of the photothermal LFIA platform for real-world applicability by detecting ultra-low levels of FtLPS spiked in blood serum samples, achieving an LOD as low as 4 pg/mL. This photothermal LFIA platform shows promise for establishing high-performance photothermal sensing in point-of-care settings and holds great potential for future advancements in rapid, on-site screening of infectious diseases.