Ligand Engineering-Based High-Efficiency Photothermal Sensors Powered Sensitive Lateral Flow Immunoassay Platform

The photothermal lateral flow immunoassay (LFIA) has garnered considerable attention, owing to its suitability for on-site quantitative detection. Furthermore, it has distinct advantages in further constructing sensitive detection methods for low-concentration targets. In this study, we employed a ligand engineering strategy to synthesize Fe³⁺-chelated quinone nanoparticles (FQNPs). Quinones with different structures, namely, naphthazarin, quinizarine, purpurin, and tetrahydroxyanthraquinone (THAQ), served as ligands to fabricate a series of FQNPs. Among them, FQNPs based on tetrahydroxyanthraquinone (FQNPs-T) exhibited exceptional light absorption ability (molar extinction coefficient = 12.71 × 10¹⁰ M^–1 cm^–1) and photothermal conversion efficiency (η = 60.32%). Subsequently, a photothermal LFIA based on FQNPs-T (FQNPs-LFIA) was developed for the detection of chlorantraniliprole (CHL) in apple and chili. The FQNPs-LFIA enables the highly sensitive detection of CHL within 25 min with a limit of detection (LOD) of 0.021 ng mL^–1, which was 8.77-fold lower than that of conventional gold nanoparticle-based LFIA (0.193 ng mL^–1). The average recovery rates of FQNPs-LFIA were 84.29–113.58%, with coefficients of variation of 4.20–14.84%. Overall, this study demonstrates the potential of FQNPs-LFIA for the sensitive and accurate detection of CHL, and it paves the way for the rapid screening of other food contaminants.