Portable Smartphone Platform Using Ratiometric Fluorescent Paper Strip for Visual Quantitative Sensing

Instrument-free, portable and direct read-out mini-devices have wider application prospects in various fields, especially for real-time/on-site sensing. Herein, combined with paper strip, a smartphone sensing platform integrated with a UV lamp and dark cavity has been developed for the rapid, sensitive, instrument-free and visual quantitative analysis in real-time/on-site conditions. The platform proved the feasibility for visual quantitative detection of pesticide via a fluorescence “on-off-on” response with a single dual-emissive ratiometric paper strip. Red-emitting CdTe quantum dots (rQDs) were embedded into the silica nanoparticles (SiO2 NPs) as an internal reference, while blue-emitting carbon dots (bCDs) as a signal report unit were covalently linked to the outer surface of SiO2 NPs. The blue fluorescence could be quenched by gold nanoparticles (Au NPs) and then recovered with pesticide. The Red (R), Green (G) and Blue (B) channel values of the generated images were determined by a Color Recognizer...