A novel kind of nitrogen-doped carbon dots (N-CDs) with strong blue fluorescence emission was synthesized via microwave pyrolysis method using humic acid, urea, and citric acid as the precursor. We found that the fluorescence emission of N-CDs can be firstly quenched by Fe³⁺ (turn-off) and then recovered by glutathione (turn-on). Moreover, N-CDs applied as an “on-off-on” fluorescent sensor for the detection of Fe³⁺ and glutathione (GSH) was further studied in this work. N-CDs showed good selectivity and sensitivity towards Fe³⁺ than other metal ions, and the limit of detection (LoD) is lower to 0.102 μM. Furthermore, the stable N-CDs/Fe³⁺exhibited a high sensitivity detection for GSH with a LoD of 0.226 μM. In addition, density functional theory calculations were further performed to reveal the mechanism of the “turn-off” and “turn-on” process. According to geometries and frontier molecular orbital (FMO) results, N-CDs exhibited strong interaction with Fe³⁺ rather than other metal ions, and the N-CDs/Fe³⁺ complex exhibited the highest stability among other complexes. Furthermore, this “on–off–on” fluorescent sensor was successfully applied as a stain-screening detector for Streptococcus thermophilus with high production of GSH.

以腐殖酸，尿素和柠檬酸为前驱体，通过微波热解法合成了一种新型的强氮荧光的氮掺杂碳点（N-CDs）。我们发现，N-CDs的荧光发射可以首先被Fe ³⁺淬灭（关闭），然后被谷胱甘肽恢复（打开）。此外，在这项工作中还进一步研究了N-CD作为“开-关-开”荧光传感器检测Fe ³⁺和谷胱甘肽（GSH）的方法。N-CD与其他金属离子相比，对Fe ³⁺具有良好的选择性和灵敏度，检测限（LoD）降至0.102μM。此外，稳定的N-CD / Fe ³⁺对GSH的检测灵敏度高，LoD为0.226μM。此外，进一步进行了密度泛函理论计算，以揭示“关闭”和“开启”过程的机理。根据几何结构和前沿分子轨道（FMO）结果，N-CDs与Fe ³⁺而不是其他金属离子具有很强的相互作用，N-CDs / Fe ³⁺配合物在其他配合物中表现出最高的稳定性。此外，这种“开-关-开”荧光传感器已成功用作具有高GSH产量的嗜热链球菌的污点筛选检测器。