Smartphone-integrated colorimetric and ratiometric fluorescence sensor for visual detection of HSO₄

The detection of bisulfate (HSO₄^-) is critical in food preservation and pharmaceutical quality control, as it is a common additive with potential health risks. Existing detection methods often lack the portability for on-site analysis or the capability for cross-validation to ensure accuracy. Establishing a rapid and reliable quantitative method for HSO₄^- is the prerequisite and core step for precisely controlling related food and pharmaceutical additives.

To address the need for a rapid, reliable, and field-deployable sensing platform that provides intuitive visual feedback and quantitative data for HSO₄^- detection in complex real-world samples, we engineered a novel Schiff base probe (KF) integrating aggregation-induced emission (AIE), excited-state intramolecular proton transfer (ESIPT), and intramolecular charge transfer (ICT) properties. HSO₄^- triggers a specific cleavage of the probe's imine bond, inducing a distinct colorimetric change (yellow to colorless) and a ratiometric fluorescence shift (yellow-green to blue). This dual-signal response enables visual qualitative analysis and provides an internal reference for quantitative measurement, with a fluorescence detection limit down to 72.9 nM. We integrated the probe with a smartphone-based RGB analysis platform (ColorPicker App), creating a portable device for on-site, quantitative determination. The platform's efficacy was successfully demonstrated by accurately detecting HSO₄^- in spiked vegetable and pharmaceutical samples with satisfactory recovery rates (83.1 %-114.4 %).

This work presents the first multifunctional probe combining AIE, ESIPT, and ICT for HSO₄^--triggered cleavage, enabling a dual-mode response. This study is significant for establishing a robust, smartphone-integrated sensor that transcends laboratory confines, offering a practical solution for on-site monitoring in food safety and pharmaceutical analysis.