|Place of Conferral||北京|
|Keyword||碳点 重金属检测 氮化碳 荧光成像|
作为碳材料的新成员，碳点的出现受到了广泛的关注。与传统的碳材料相比，碳点由于尺寸较小,表现出一些特殊的性质，例如可以更好的分散在水中，具有较高的比表面积。更有趣的是在一定波长的光照下碳点可以发出荧光，并且具有优异的稳定性和较高的量子产率。因此，碳点被广泛的应用在传感和生物成像领域中。本论文针对碳点的制备及其在传感和成像中的应用做了以下工作：（1）在先前的工作中我们发现DNA分子经过水热之后，可以制备出蓝色的荧光碳点来，而且这种荧光可以被汞和银离子猝灭，因此开发了一种可以同时检测汞和银离子的荧光探针。为了进一步确定上述实验的传感机理,我们采用DNA的基本单元：A腺嘌呤、G鸟嘌呤、C胞嘧啶和T胸腺嘧啶这四种脱氧核苷酸，把它们作为碳源，通过水热的方法进行碳点的制备，结果发现只有胞嘧啶和胸腺嘧啶可以产生荧光，并且胸腺嘧啶制备的碳点（cyt-dot）产生的荧光可以选择性的被汞离子猝灭。与DNA制备的碳点相比，它对汞离子的检测灵敏度更高，检测限更低。针对此现象我们对传感机理进行了探究，发现制备的cyt-dot含有更多的N元素,故N元素的增加可能是导致其对汞离子传感性能提高的原因。（2）基于上一个工作的结论，我们采用N元素含量更高的2，4，6-三氨基嘧啶为前驱体，通过一步水热的方法制备出荧光碳点，命名为TAPI-dots。通过XPS分析发现制备的碳量子点的N含量高达41 %。据我们所知，这是目前N元素含量最高的碳点。制备的TAPI-dots在365 nm的紫外灯下发出蓝色的荧光，通过测定相对量子产率可达到75%。此外，在pH值为6和pH值为11时，荧光可以被银离子和汞离子猝灭，其检测限分别为11.4 nM和10.3 nM。在实际水样分析中，这种传感方法显示出宽的线性范围和高的回收率。针对这种选择性可控的荧光探针我们测定了它荧光猝灭前后的荧光寿命，发现了两种不同的荧光猝灭的机理。借助不同pH条件下碳点表面离子的变化规律，提出了一种新的pH辅助传感重金属的机理。（3）为了进一步提高N元素的含量，我们采用氮含量更高的三聚氰胺为前驱体。由于三聚氰胺不溶于水而且在有水的条件下易于分解的原因,故无法采取水热方法制备。于是我们将三聚氰胺高温煅烧2小时，未经冷却后直接在冷水中超声10 min，然后制备得到CN-dots。这种高温骤冷制备CN-dots的方法相比酸切方法和长时间超声方法,更加的简单、快速。通过对原子力显微镜和透射电镜的结果分析可知制备CN-dots粒径在2 nm左右，高度为2碳氮的原子层。制备的CN-dots具有良好的水分散性而且发出蓝色的荧光，并且具有双光子荧光的特性。基于此我们将制备的CN-dots与HeLa细胞孵育4个小时后，在荧光显微镜和双光子显微镜下得到清晰的细胞图像。
As a new member of carbon materials, carbon dots have attracted much researchers’ attention since it was first reported. Owning to its small size, carbon dots usually exhibit water dispersibility and larger surface area. More important, they can emit fluorescence (FL) with high quantum yield and good photo-stability. Thus, carbon dots have been wildly studied in FL sensing and bio-imagine. The primary content of this thesis was focused on the synthesis of N doped carbon dots and their application in sensing and bio-imaging.(1) Recently, our group had synthesized a new type of bio-dots and used for detection of Hg(II) and Ag(I). To confirm the sensing mechanism, four DNA units: adenine (A), cytosine (C), thymine (T), and guanine (G) were used to prepared carbon dots via hydrothermal method. However, only cytosine produced CDs and emit fluorescence which could be selectively quenched by Hg(II) with low limit of detection. In view of this phenomenon, we explored the sensing mechanism and found that the increase of nitrogen element may be an important reason for its sensitivity to Hg(II) ions.(2) Based on the above result, we plan to prepare carbon dots which containing higher N element using 2,4,6-Triaminopyrimidine (TAPI) as precursor. From XPS results, the obtained carbon dots were found to contain 41 at. % nitrogen, which was significantly higher than similar materials reported previously. Under the 365 nm lamp, the carbon dots emitted bright blue fluorescence the quantum yield as high as 75%. Moreover, the fluorescence was selectively quenched by Hg(II) at pH of 6 and Ag(I) at pH of 11, with detection limits of 11.4 nM and 10.3 nM, respectively. In the lake water analysis, the nitrogen rich carbon dots exhibited high sensitivity, wide linear range and satisfactory recovery, suggesting that they are suitable to be used as probes for Hg(II) and Ag(I) detection. By analyzing the fluorescence lifetime of the carbon dots, different mechanisms of fluorescence quenching were revealed for Hg(II) and Ag(I). Based on that, a sensing mechanism of pH assisted selective detection was proposed.(3) To further increase the content of N, we used melamine as a precursor. However, as melamine is insoluble in water and would decompose under water conditions. Thus, we heated melamine at 520 oC about 2 hours, then cooling it directly in cold water and ultrasonic about 10 min. In compared with previous methods such as acid digestion or ultrasound, it is easy-operation and short time-consuming. The prepared CN-dots was about 2 nm and the height was about 1.2 nm. Meanwhile, it could emit blue fluorescence under excitation of 365nm lamp. Moreover, we incubated CN-dots and HeLa cells for 4 hours, and obtained clear cell images under FL microscope and two-photon microscope, suggesting its great potential application in bio-imaging.
|罗亮. 氮掺杂荧光碳点的制备及其传感和成像性能研究[D]. 北京. 中国科学院大学,2018.|
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