Photoresponsive oxidase-like phosphorescent carbon dots in colorimetric Hg2+ detection

Developing novel photoresponsive oxidase mimics is highly useful for environmental pollution monitoring and biological sensing. Herein, long-life room-temperature phosphorescent nitrogen-doped carbon quantum dots (P-NCDs) were synthesized from triethylenetetramine hexaacetic acid via a simple one-step hydrothermal method. The P-NCDs showed high photoresponsive oxidase-like activity. On this basis, a P-NCD-based photostimulated colorimetric sensing system was developed and used to detect Hg2+ in environmental and biological samples. P-NCDs under 365 nm UV lamp irradiation converted dissolved oxygen, via triplet excited state (T1) exciton transfer, to singlet oxygen (1O2), which then oxidized 3,3′,5,5′-tetramethylbenzidine (TMB), leading to a color changing reaction. Cysteine can suppress the catalysis of P-NCDs, and its specific complexation with Hg2+ can recover the oxidation activity of P-NCDs. Hence, efficient colorimetric Hg2+ detection with a linear range of 0.01–14 μM and a detection limit of 3.1 nM was achieved by detecting the color change of TMB. The feasibility of this strategy was validated through real sample analysis. Our study broadens the application scope of phosphorescent nanomaterials into colorimetric sensing.