A versatile ratiometric nanosensing approach for sensitive and accurate detection of Hg2+ and biological thiols based on new fluorescent carbon quantum dots

Herein, we first reported a facile synthesis method for fabrication of highly photoluminescent carbon quantum dots (CQDs) using sodium alginate as the carbon source and histidine as both the nitrogen source and functional monomer by one-pot hydrothermal synthesis. The as-prepared CQDs gave a high quantum yield of 32%. By employing the new CQDs and rhodamine B (RhB), we demonstrated a simple, facile, sensitive, and accurate ratiometric sensor for detection of Hg2+ and biological thiols. The photoluminescence of CQDs in the ratiometric sensor can be selectively and intensively suppressed by Hg2+ due to strong electrostatic interaction between the surface functional groups of the CQDs and Hg2+. When glutathione (GSH) was introduced into the “Turn Off” CQDs-RhB-Hg2+ sensing system, the fluorescence of the CQDs can be recovered rapidly due to the stronger affinity between thiol and Hg2+, while the fluorescence of the RhB remained constant in this sensing process. Based on the above principle, the ratiometric strategy for detecting Hg2+ and GSH can be achieved readily, and gives satisfactory limit of detections (LODs) of 30 and 20 nM for Hg2+ and GSH, respectively. The dual-emission fluorescent CQDs-RhB sensor does not need the complicated molecular design and the synthesis of dual-emission fluorophores. Meanwhile, the feasibility of the proposed method for analysis of water samples, food samples, and biological samples (plasma from mice oxidative stress study) was investigated. The developed ratiometric nanosensor is proven to be facile, with less sample consumption, rapid, lost cost, highly sensitive, and very selective for Hg2+ and biological thiol detection, which offers a new approach for environmental, food, and biological analysis.