碳点(Carbon dots, CDs)作为一种新颖的零维碳基纳米材料，因光学活性优越、细胞毒性低、生物相容性好等优点引起了广泛关注。基于CDs的荧光探针具有合成成本低、操作简便、水溶性好、光稳定性优异等优势，因而适用于环境和生物体内活性离子的检测与成像。本文合成了三种氮掺杂表面功能化荧光碳点并探究了其结构特征、荧光性能、传感能力、识别机理以及成像应用。

主要工作如下：

(1) 氮掺杂羟基表面功能化荧光碳点的合成及其对ClO⁻的检测

采用聚乙烯吡咯烷酮、柠檬酸和精氨酸为原料在水热条件下合成了CDs(N-CDs)。透射电镜图像(TEM)、X射线光电子能谱(XPS)和傅里叶变换红外光谱(FT-IR)等方式证明N-CDs平均尺寸为1.74±0.28 nm，具有氮掺杂羟基表面功能化的结构特性。不仅如此，N-CDs具有优异且稳定的荧光性能及良好的选择性识别行为，可作为“on-off”型荧光探针实现对ClO⁻的特异性检测，在0.1-100 μmol·L⁻¹范围内有良好的线性关系，检测限为 0.01 μmol·L⁻¹。由N-CDs制成的检测试纸在10 min内实现了实际样品中ClO⁻的可视化检测。3-(4,5-二甲基噻唑-2-)-2,5-二苯基四氮唑溴盐(MTT)实验结果证明了N-CDs具有出色的生物相容性和低细胞毒性，成功用于活细胞中ClO⁻的传感成像。

(2) 氮硫共掺杂甲硫氨酸表面功能化荧光碳点的合成及其对Fe³⁺和抗坏血酸的检测

在氮掺杂的基础上通过加入甲硫氨酸合成了氮硫共掺杂甲硫氨酸表面功能化荧光CDs(N,S-CDs)。N,S-CDs具有优异的量子产率29.4%，可作为荧光探针通过“on-off-on”过程高选择性和灵敏性检测Fe³⁺和抗坏血酸(AA)且不受其他共存离子的干扰，在0.01-800 μmol·L⁻¹和0.01-50 mmol·L⁻¹范围内分别对Fe³⁺和AA呈现良好的线性关系，检测限分别低至0.26 nmol·L⁻¹和17.6 μmol·L⁻¹，并成功实现了活细胞中Fe³⁺和AA的成像。基于N,S-CDs制备的检测试纸和水凝胶可作为固体传感器用于溶液中Fe³⁺和AA的实时监测。此外，含有N,S-CDs的荧光油墨在信息加密传输和图案防伪印刷方面取得了良好效果。

(3) 氮掺杂表面功能化荧光碳化聚合物点的合成及其对Cu²⁺和S^2–的检测

通过增加褐煤，调整聚合物用量得到了一种新型CDs—碳化聚合物点(Carbonized polymer dots, CPDs)，结构表征证实其具有独特的核壳结构，且表现出优越的光学性能、良好的水溶性、出色的生物相容性和低毒性。CPDs可作为“on-off-on”型荧光探针用于对溶液中Cu²⁺和S^2–的选择性传感，检测限分别为0.059 μmol·L^–1和 0.032 μmol·L^–1。智能手机中的颜色识别软件通过捕捉基于CPDs检测试纸的荧光变化，在1 min内实现了现场实时可视化测定Cu²⁺和S^2–的浓度。CPDs也可作为荧光油墨成功用于信息加密和防伪印刷。

Carbon dots (CDs), as a novel zero-dimensional carbon based nanomaterials, have attracted widespread attention due to superior optical activity, low cytotoxicity and good biocompatibility. Fluorescent probes based on CDs have the advantages of low synthesis cost, easy operation, good water solubility and excellent photostability, which are suitable for the detection and imaging of reactive ions in the environment and organisms. In this paper, three nitrogen doped and surface functionalized fluorescent CDs were synthesized and their structural features, fluorescence properties, sensing abilities, recognition mechanisms and imaging applications were investigated.

The main work is as follows:

(1) Synthesis of nitrogen doped hydroxyl surface functionalized fluorescent carbon dots and their detection of ClO⁻

The CDs (N-CDs) were synthesized by using polyvinylpyrrolidone, citric acid and arginine as raw materials under hydrothermal method. Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) demonstrate that the N-CDs have an average size of 1.74±0.28 nm and possess structural properties of nitrogen doped hydroxyl surface functionalization. In addition, N-CDs have stable and excellent fluorescence luminescence performance and good selective recognition behavior, which can be used as "on-off" fluorescent probes to achieve specific detection of ClO⁻, with a good linear relationship in the range of 0.1-100 μmol·L^–1 and the detection limit was 0.01 μmol·L^–1. The test paper fabricated with N-CDs enables the visual detection of ClO⁻ in the samples within 10 min. The results of 3-(4,5-dimethylthiazol-2-)-2,5-diphenyltetrazolium bromide (MTT) experiments prove that the N-CDs have excellent biocompatibility and low cytotoxicity, successfully applied to the sensing imaging of ClO⁻ in living cells.

(2) Synthesis of nitrogen and sulfur co-doped methionine surface functionalized fluorescent carbon dots and their detection of Fe³⁺ and ascorbic acid

The CDs (N,S-CDs) co-doped with nitrogen and sulfur and surface functionalized with methionine were synthesized on the basis of nitrogen doping by introducing methionine. The N,S-CDs have excellent quantum yield (29.4%) and can serve as fluorescent probes for the highly selective and sensitive detection of Fe³⁺ and ascorbic acid (AA) through "on-off-on" process without interference from other co-existing ions, which show good linearity in the range of 0.01-800 μmol·L^–1 and 0.01-50 mmol·L^–1 for Fe³⁺ and AA, with the detection limits of 0.26 nmol·L^–1 and 17.6 μmol·L^–1, respectively, and the imaging of Fe³⁺ and AA in living cells are successfully achieved. The test paper and hydrogel prepared based on N,S-CDs can be utilized as solid sensors for real-time monitoring of Fe³⁺ and AA in solution. In addition, fluorescent inks containing N,S-CDs achieve good results in the encrypted transmission of information and anti-counterfeiting printing of patterns.

(3) Synthesis of nitrogen doped surface functionalized fluorescent carbonized polymer dots and their detection of Cu²⁺ and S^2–

Carbonized polymer dots (CPDs), a new type of CDs, were prepared by adding lignite and increasing the polymer content, and structural characterization confirms that they have unique core-shell structures and exhibit superior optical properties, good water solubility, prominent biocompatibility and low toxicity. As "on-off-on" fluorescent probes, CPDs can achieve selective sensing of Cu²⁺ and S^2– in solution with detection limits of 0.059 μmol·L^–1 and 0.032 μmol·L^–1, respectively. The color recognition software in smartphone allow on-site real-time visual detection of Cu²⁺ and S^2– concentrations within 1 min by capturing the fluorescence changes of the CPDs-based test paper. CPDs can also be successfully used as fluorescent inks for information encryption and anti-counterfeiting printing.