Spatial Configuration-Directed Screening of Isomer-Derived Carbon Dots for Highly Selective Sensing of Nitrite in Food and In Vivo Imaging

Fluorescence sensing technology based on carbon quantum dots (CDs) has garnered significant attention due to its high sensitivity and operational simplicity. However, research on regulating CDs' performance and sensing mechanisms through spatial configuration control of precursors remains relatively underdeveloped. This study employed three isomers of benzidine as carbon sources, synthesizing corresponding CDs via a solvothermal method. The size distribution and band structure of the CDs were significantly different due to isomer-induced polymerization differences, as validated by both experimental characterization and density functional theory calculations. Among these, MPD-CDs synthesized from m-phenylenediamine exhibited the most favorable comprehensive performance. A fluorescence sensor based on MPD-CDs achieved highly sensitive detection of NO2- in food, with a detection limit of 0.22 µM, primarily through diazotization-coupling reactions between MPD-CDs and NO2- causing static fluorescence quenching. Furthermore, cell viability exceeded 80% after incubation with 100 µg/mL MPD-CDs, enabling successful application in mouse in vivo imaging. This study provides theoretical and experimental foundations for screening and designing high-performance CD-based fluorescent sensing platforms, offering broad application prospects in food safety detection and bioimaging analysis.