Ratiometric fluorescence probe based on lipase coated Au NCs covalently linked to FITC for smartphone-integrated dual-mode detection of paraquat.

The use of paraquat (PQ) poses significant environmental and health risks, necessitating the development of rapid and sensitive detection methods. Herein, a novel ratiometric fluorescent probe, FITC-Lip-Au NCs, was constructed by covalently linking fluorescein isothiocyanate (FITC) to Lip-Au NCs prepared using lipase (Lip) as a pioneering protein template for the selective and visual detection of PQ. Upon PQ interaction, FITC-Lip-Au NCs showed electrostatic interaction-assisted dynamic quenching at 650 nm and a constant signal at 520 nm, enabling a LOD of 15 nM and a linear range of 0.025-45 μM. Leveraging the distinct color change, paper-based and hydrogel-film sensors coupled with smartphone RGB analysis enabled on-site visual and quantitative detection of PQ. This work not only expanded protein template diversity for nanocluster synthesis but also presented a reliable, rapid, and dual-mode sensing strategy for monitoring PQ residues in food quality and safety.