Boron-doped carbon dots with integrated functions: Highly sensitive pH monitoring, pH-triggered information encryption, and versatile vitamin B12 detection.

Fluorescent sensors are pivotal in environmental and bioanalysis owing to their high sensitivity and rapid response. Among them, carbon dots (Cdots) stand out as ideal platforms for multifunctional sensing. Their tunable fluorescence and excellent biocompatibility facilitate the integration of multiple detection modalities, enabling versatile analyte detection. This capability can be further enhanced through heteroatom doping. Notably, boron doping introduces defect sites and active functional groups, providing a powerful strategy for developing advanced sensors suited for challenging applications in complex media. In this work, boron-doped yellow fluorescent carbon dots (BCdots) were synthesized via a green, facile approach to construct a dual-mode fluorescence/colorimetric sensing system for pH and vitamin B12 (VB12) detection. The fluorescence-based pH sensing operates on a protonation-induced enhancement mechanism, enabling ultrasensitive dynamic monitoring within a linear range of pH 2.5-6.0. For VB12 sensing, fluorescence quenching occurs via an inner filter effect (IFE) between VB12 and BCdots, yielding a wide linear range of 0.47-359.12 μM and a low detection limit of 80.15 nM. The colorimetric mode also displayed excellent sensitivity, with a linear range of 0.70-219.64 μM and a detection limit of 0.12 μM. Real sample analyses validated accuracy and reproducibility of the dual-mode fluorescence/colorimetric sensing platform, achieving recoveries of 95.74%-108.85% and RSDs below 3.33%. This study presents a carbon-based dual-mode sensor for the simultaneous detection of pH and vitamin B12, leveraging a synergistic integration of fluorescence and colorimetric detection. The developed platform demonstrates high precision, strong selectivity, and reliable performance in complex sample matrices. This work provides a crucial methodology for advancing multifunctional sensing tools in environmental monitoring and biomedical diagnostics.