<scp>l</scp>-Cysteine-Functionalized Boron-Doped Graphitic Carbon Nitride Quantum Dots: A Biocompatible Fluorescent Sensor for Cadmium Detection in Water
Samarjit Pattnayak, Shubhalaxmi Choudhury, Ugrabadi Sahoo, Pragnyashree Aparajita, Surajita Sahu, Monalisa Mishra, Riya Adhikari, Garudadhwaj Hota
Abstract
Boron-doped graphitic carbon nitride quantum dots (B-gC 3 N 4 QDs) are synthesized through a simple thermal process and functionalized with l -Cysteine ( l -Cys) via an EDC/NHS coupling reaction. The resulting l -Cys/B-gC 3 N 4 QDs demonstrate a high quantum yield of 28%, excellent water solubility, and resistance to photobleaching and ionic strength. These quantum dots are employed as fluorescent probes for detecting Cd 2+ ions at trace levels in water. They exhibit a fluorescence signal enhancement in response to Cd 2+ ions, attributed to a chelation-enhanced fluorescence (CHEF) mechanism. The sensor detects Cd 2+ ions within a linear range of 0.1–0.7 μM, with a detection limit of 0.23 μM and a binding constant of 9.83 × 10 5 M –1 . Cytotoxicity assays reveal that l -Cys/B-gC 3 N 4 QDs, both alone and in the presence of Cd 2+, show no DNA damage or cell membrane disruption, confirming their nontoxic nature. Furthermore, the sensor achieves high accuracy in detecting Cd 2+ in real water samples, with recovery rates ranging from 95 to 106%. This work presents a sustainable, biocompatible, and cost-effective fluorescent probe for real-time monitoring of cadmium ions in environmental water sources.