Dual-readout fluorescence 'turn-on' lateral flow immunoassay for sensitive detection of imidacloprid

Although imidacloprid (IMI) is a widely used, highly efficient, and broad-spectrum insecticide, it poses a serious threat to pollinators such as bees, which can significantly impact crop harvests. Therefore, there is an urgent need to develop a sensitive, portable, and economical method for detecting IMI. This study establishes a novel dual-readout fluorescence 'turn-on' mode lateral flow immunoassay (LFIA) based on the inner filter effect (IFE) for the detection of IMI. The assay combines hollow gold nanoparticles (HAuNPs) and ultra-bright red luminescent bovine serum albumin (BSA)-stabilised gold nanoclusters (BSA-AuNCs) as quencher/donor pairs. HAuNPs effectively quenched the red-emitting fluorescence of BSA-AuNCs due to the higher IFE efficiency resulting from the spectral overlap. The dual-readout immunosensor exhibited fluorescence and colorimetric responses for IMI within 16 min, with limits of detection (LOD) of 7.8 and 47.8 pg/mL for fluorescence and colorimetric modes, respectively. The fluorescence mode thus attained an approximately six-fold decrease in detection limits compared with conventional gold nanoparticle-based LFIA (AuNPs-LFIA). The dual-readout fluorescence 'turn-on' immunosensor showed a good recovery range of 82.40-113.80 % for detecting IMI in real samples, with a relative standard deviation (RSD) below 11.88 %. Thus, the developed immunosensor may be used as a rapid and highly sensitive tool for the detection of hazardous substances in practical applications.