Background-Free and Reversible Upconversion Hydrogel Sensing Platform for Visual Monitoring of Sulfite

Abstract

Excessive sulfite usage in food and pharmaceutical production causes respiratory and neurological diseases, underscoring the need for a sensitive and rapid quantification strategy. The portable sensing platform based on a luminescent hydrogel sensor is a powerful tool for the on-site, realtime detection of sulfite ions. However, the lack of recyclability in almost all reaction-based hydrogel sensors increases the application cost. This study constructed a reversible and upconversion nanoprobe combining upconversion nanoparticles (UCNPs) and pararosaniline (PAR) for sulfite detection. The upconversion nanoprobe was further encapsulated in a three-dimensional polyacrylamide hydrogel matrix to create a background-free, reversible hydrogel sensor. The near-infrared excitation of UCNPs avoids the autofluorescence in the hydrogel and real samples. Meanwhile, PAR serves as a specific recognition unit for sulfite ions. After the addition of sulfites, a specific reaction occurs between PAR and sulfites, leading to the recovery of characteristic emission at 540 nm, achieving sensitive detection of sulfite ions. Importantly, this specific reaction is reversible under thermal treatment, allowing the hydrogel sensor to return to its initial state and thus enabling reversible detection of sulfite ions. Furthermore, a portable sensing platform is developed to realize point-of-care, real-time quantitative detection of sulfite ions. The proposed upconversion reversible hydrogel sensor provides a new sensing strategy for the detection of hazardous substances in food and offers new insights into the preparation of reversible, highly sensitive hydrogel sensors.

Synthesis of Naphthalimide Azocarboxylates Showing Turn‐On Fluorescence by Substitution Reaction with Sulfinates**

“…In fact, the sensing or detection of toxic inorganic sulfite (SO 3 2À ) has been wellstudied using this strategy. [7,8] On the other hand, target labeling in chemical biology requires the formation of covalent bonds with the appropriate labeling molecules for post-labeling analysis, such as proteomics. However, efficient labeling methods for sulfinates are still under development due to their weak nucleophilicity and electrophilicity compared to other sulfur functional groups such as sulfanyl (R-SH) and sulfenyl (R-SOH) groups.…”