Boron Doped Carbon Dot Integrated Fluorescent Hybrid Microgels: A Smart and Responsive Framework for Sensing of Salicylic Acid

The increasing prevalence of salicylic acid as an unauthorized adulterant in milk and its derived products poses serious concerns for human health and safety. In this study, a fluorescent probe based on boron-doped carbon dot-integrated poly(N-isopropylacrylamide) microgels (BCQDs@PNIPAM) was developed for the selective and sensitive detection of salicylic acid. The incorporation of carbon quantum dots (CQDs) within the PNIPAM microgel matrix not only imparts strong fluorescence but also minimizes their inherent tendency to self-aggregate, thereby enabling a stimuli-responsive sensing platform for salicylic acid detection. The biocompatibility of the developed probe was further evaluated through seed germination and bacterial assays. Moreover, the introduction of electron-deficient boron into the CQDs enhances their fluorescence performance, improving selectivity and quick response with "turn-on" signal for salicylic acid. Using this strategy, the probe demonstrated a linear detection range of 1-240 µM with a low limit of detection (LOD) of 54 nM. The feasibility of the sensing platform was demonstrated in real samples, highlighting its potential in quality control in food products. In addition, the enhanced fluorescence characteristics of the hybrid microgels enabled their application in security and anti-counterfeiting systems. Overall, this work offers a reliable and sustainable sensing platform for ensuring milk quality and safety, with promising implications for food surveillance and public health protection.