A dual signal immunochromatographic strip for the detection of imidaclothiz using a recombinant fluorescent-peptide tracer and gold nanoparticles

• Fluorescent peptide tracer is successfully used to develop dual signal ICS. • Sensitivity of the ICS is significantly improved by employing the peptidomimetic. • The “turn-on” mode makes the result more intuitive and avoid the misinterpretation. • Fluorescent peptide tracer does not suffer from batch-to-batch variability. • The dual signal ICS is low-cost and environmentally friendly. Immunochromatographic strips (ICS) attract much attention as practical analytical tools, particularly for point of care testing. However, ICS suffer from insufficient sensitivity, especially for small molecules. Competitive assays developed with analyte peptidomimetics obtained from phage display peptide libraries, usually enable to attain lower detection limits than the widely used chemical haptens, but are rarely used in ICS assay because of the shortcomings of the phage particle. In this work, we used a phage-free fluorescent peptide tracer (C2-15-EmGFP) for ICS, which consists of the emerald green fluorescent protein (EmGFP) fused to a peptidomimetic of imidaclothiz (C2-15). C2-15-EmGFP works as fluorescent donor and colloidal gold nanoparticles (AuNPs) coated with an anti-imidaclohtiz antibody as quencher, which allowed to develop a fluorescence quenching-based ICS (FQICS) for the detection of imidaclothiz in agricultural and environmental samples. The colorimetric and fluorescent signals were determined by both naked eye and imageJ software. Quantitative image analysis showed that the sensitivities obtained using the colorimetric (50% inhibitory concentration (IC 50 ): 9.62 ng mL −1 ) and fluorescent (50% saturation concentration (SC 50 ): 10.1 ng mL −1 ) signals were similar. The visual detection by the naked eye showed a sensitivity of 8.00 ng mL −1 with fluorescent readout which was 8-fold lower than that of the colorimetric readout (64.0 ng mL −1 ). The FQICS performed with excellent recoveries and good correlation with high-performance liquid chromatography in different matrices.