Synthesis of Up-Conversion Fluorescence N-Doped Carbon Dots with High Selectivity and Sensitivity for Detection of Cu2+ Ions

Carbon dots have drawn extensive attention in the detection of metal ions with good stability, excellent biocompatibility and low toxicity. Meanwhile, the quantum yield, response rate and the detection mechanism for Cu2+ ions are vital to their development and application. To obtain more selective and sensitive materials to detect Cu2+ ions, N-doped carbon dots (DN-CDs) were synthesized by a one-step hydrothermal method using citric acid as the carbon source and diethylenetriamine (DETA) as the nitrogen source. The obtained DN-CDs exhibited stable and intense blue light emission and special near-infrared up-conversion fluorescence at 820 nm, attributed to the effect of introducing N atoms into the structure of carbon dots. Due to the dynamic quenching of the DN-CDs by Cu2+ ions, the fluorescence intensity (lambda ex = 820 nm) of DN-CDs was quantitatively decreased in the presence of Cu2+ ions. The DN-CDs had a rapid response within 3 min. The DN-CD system exhibited a linear relationship with a concentration range from 2.5 to 50 mu M and low detection limit (LOD) of 42 nM. After careful investigation, an interesting conclusion was proposed: N-doped CDs with N/O = 1:1 or higher with relatively abundant N atoms prefer to detect Cu2+ ions while those with N/O = 1:2 or lower prefer to detect Fe3+ ions.