A Fluorescent Probe Based on Carbazole and Benzoindole for On‐Site Detection of Sulfite

Design, synthesis and DFT analysis of a highly selective chromenylium based fluorescent probe for cellular imaging and selective detection of sulfite ions

Sulfite (SO32−) is a significant analyte that is frequently employed as a food and beverage sector preservative but its excessive consumption might lead to negative health effects. Therefore, it is important to develop ultra-sensitive and ultra-selective sulfite detection methods. Herein, we demonstrate the design, synthesis and application of a highly selective fluorescent probe for fast and sensitive detection of sulfite ions. The interaction between this probe and SO32− ions induced a fluorescence signal (quenching) which made it possible to monitor the ions in a highly selective manner amongst various competing anions. Furthermore, the probe exhibited an excellent detection capability within a wide linear range and a high sensitivity with low detection limit (1.44 µM). Besides, the probe was applied for the analysis of sulfite ions in real samples as well as for cell imaging. Further validation of the suggested sensing mechanism was obtained from density functional theory (DFT) calculations, which showed substantial variation in the energy gaps between HOMO–LUMO, charge distribution, and intramolecular charge transfer (ICT). DFT calculations confirmed that the nucleophilic attack of SO32− on the π-conjugated system of the probe causes inhibition of ICT and fluorescence quenching behavior. The above findings clearly highlight the efficiency of the designed probe as an analytical tool for detecting sulfite ions in the environment and food safety applications.

A carbazole-benzothiazole-based fluorescent probe embedded in paper, cellulose, and chitosan sensors for visual and rapid detection of bisulfite in food samples.

Bisulfite (HSO3-) is widely used as a food additive, yet its excessive residue poses potential health risks. Herein, a novel fluorescent probe TC-FV-BT was developed for the detection of HSO3-. Upon addition of HSO3-, the nucleophilic addition disrupted the π-conjugation of the probe, giving rise to a distinct fluorescence enhancement with bright orange emission. TC-FV-BT exhibited a rapid response, a low detection limit of 0.077 μM, and excellent selectivity. The sensing mechanism was confirmed by 1H NMR titration, HRMS, and DFT calculations. Furthermore, TC-FV-BT was successfully immobilized onto paper, cellulose acetate (CA), and chitosan (CS) film substrates to construct a portable visual detection platform, which was applied to the analysis of HSO3- in ten complex food matrices. Notably, the CS film-based sensor displayed superior anti-interference performance in high-oil and high-pigment samples. This work provides a versatile and practical platform for on-site rapid monitoring of HSO3- in food safety applications.

Cyanide-Triggered Fluorescence Turn-On in an Indole-Based Chemodosimeter.

Colorimetric and Fluorometric Recognition of Al3+ using Thiazole-Based Schiff base: A Mini-Review.

A ratiometric fluorescent probe for HSO3− and its application in environmental and food analysis

Bisulfite (HSO3−) is widely used as a preservative and antioxidant in the food industry and chemical manufacturing, yet its excessive residues pose risks to food quality, environmental safety, and human health. To achieve rapid, selective, and quantitative detection of HSO3−, a ratiometric fluorescent probe based on a benzothiazole–carbazole unit and a benzoindole ion was developed. Upon reaction with HSO3−, the probe exhibits a distinct dual-emission response, fluorescence intensity decreases at 612 nm and increases at 467 nm, enabling robust ratiometric sensing (F467/F612). Owing to its pronounced fluorescence modulation (emission signal change > 145 nm) and high sensitivity (limit of detection = 0.62 μM), the probe demonstrates reliable performance in aqueous samples and has been successfully integrated into portable test strips and swabs. Furthermore, when coupled with a smartphone-based colorimetric application software, the probe allows convenient and real-time quantification of both gaseous SO2 and aqueous HSO3− across environmental and food-related matrices. This work thus delivers a practical, instrument-free platform for sulfite monitoring in complex real-world settings.

A ratiometric fluorescent probe based on benzothiazole with a large Stokes shift for fluoride ion sensing in living cells, animals and plants.

A novel near-infrared ratiometric fluorescent probe designed and synthesized by rationally linking dicyanoisophorone with 2-(2-hydroxyphenyl)benzothiazole provides a reliable and versatile tool for the visual monitoring of fluoride ions in both environmental and biological contexts.