Orchestrating Interfacial Carrier Dynamics and Plasmonic Coupling toward High-Efficiency Photothermal Conversion for Sensitive Point-of-Care Testing

Abstract

Current design strategies for photothermal nanotags in lateral flow immunoassay (LFIA) focus largely on enhancing light-harvesting ability, yet overlook the modulation of photogenerated carrier dynamics. This critical oversight leads to suboptimal photothermal performance of nanotags and limits the sensitivity of photothermal LFIA. Herein, we construct an Au-CuS heterostructure (CuSNPs@Au) by intimately anchoring gold nanoparticles onto CuS nanoparticles, forming a Schottky barrier at the heterointerface. The Schottky barrier promotes efficient spatial separation of photogenerated charge carriers and suppresses charge recombination, prolonging the carrier lifetime from 49.85 to 103.07 ps. The extended carrier lifetime guarantees sufficient nonradiative relaxation and thus facilitates efficient photothermal conversion. Meanwhile, benefiting from strong plasmonic coupling, CuSNPs@Au achieves an electric field enhancement factor of 82.00 and a power absorption density of 9.9 × 1020 W·cm–3, which are 11.23- and 61.88-fold higher than those of CuSNPs (7.30 and 1.6 × 1019 W·cm–3), respectively. The synergistic integration of carrier dynamics modulation and plasmonic coupling endows CuSNPs@Au with a high photothermal conversion efficiency of 56.73%, markedly higher than that of CuSNPs (39.08%). Utilizing CuSNPs@Au as photothermal nanotags, the developed CuSNPs@Au-LFIA enables sensitive detection of chlorantraniliprole with a limit of detection of 0.019 ng mL–1, representing a 10.11-fold sensitivity improvement over conventional AuNPs-LFIA. This work provides a rational strategy for designing high-performance photothermal nanotags for sensitive LFIA.