A Biocompatible Fluorescent Ink Based on Water-Soluble Luminescent Carbon Nanodots
A Biocompatible Fluorescent Ink Based on Water-Soluble Luminescent Carbon Nanodots
复制标题
基于水溶性发光碳纳米点的生物相容性荧光墨水
DOI：
10.1002/anie.201206791
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Wang, Lijun
中科院分区：
文献类型：
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作者：
Qu, Songnan;Wang, Xiaoyun;Wang, Lijun
碳纳米点（C点）是一种迷人的碳材料，与有机染料和其他具有重金属核的半导体纳米点相比，它们具有独特的优点，如化学惰性，缺乏光学闪烁，低光漂白，低细胞毒性和优异的生物相容性，因此吸引了越来越多的兴趣。[1]C点用途广泛，可用于各种技术，如生物成像，[2]生物传感器，[3]传感器，[4]激光器，[5] LED，[6]和能量转换/存储设备。[7]然而，除了有前途的生物应用，基于C-dot的固态发光器件的性能仍然不令人满意，因为在干燥和聚集状态下发生强烈的荧光猝灭。只有少数情况下，高荧光的固态材料的基础上的C-点已被报道。[8]目前，在将C点用于商业应用之前，还需要对C点进行更多的研究。碳点可以通过几种现有的技术制备，如激光烧蚀，[9]热解，[10]湿氧化，[11]超声[12]和微波辅助[13]合成，水热合成[14]和电化学蚀刻。[15]在这些方法中，微波合成已成为流行的，因为较低的相关成本比其他方法和合成是在一个步骤中实现。为了实现发光C点，通常需要表面钝化试剂，并且报道的没有表面钝化的C点的量子产率相对较低（约1%）。Qu等人报道了一种微波辅助的一步法，包括添加微量的无机离子，用于合成发光C点而不进行表面钝化。[13a]然而，这些微波合成的发光C点的量子产率通常小于10%。在此，我们报道了一种简单、低成本、一步微波合成水溶性发光C点的方法，以及它们作为一种新的生物相容性荧光油墨的应用。首先，将柠檬酸（3g）和尿素（3g）加入到蒸馏水（10 mL）中以形成透明溶液。然后将溶液在家用750 W微波炉中加热4-5分钟，在此期间溶液从无色液体变为棕色，最后变为深棕色簇状固体，表明形成了C点。然后将该固体转移到真空烘箱中，并在608 ℃下加热1小时以除去残留的小分子。将C-点的水溶液在离心机中纯化（3000分钟，20分钟）以除去大的或聚集的颗粒。所得有色（棕色）水溶液在各种浓度下保持无限期稳定。使用透射电子显微镜（TEM）和原子力显微镜（AFM）的C-点的形态进行了表征。将C点的稀水溶液的液滴沉积在用于TEM的碳涂覆的铜网格上和用于AFM的玻璃和硅衬底上。TEM图像（图1a）和AFM图像以及相关的高度分析（参见支持信息，图S6和S7）表明，C点为球形且分散良好，直径范围为1-5 nm。C点的XRD图谱（图1b）显示出两个中心位于6.8和3.4的宽峰，这归因于高度无序的碳原子，类似于石墨晶格间距。[16]元素分析揭示C点的组成为C 41.54重量%、H 4.41重量%、N 20.79重量%和O（计算的）33.12重量%，因此表明这些点是富碳纳米点。C点的拉曼光谱（图1c）在1365.
Carbon nanodots (C-dots) are fascinating carbon materials that are attracting increasing interest because they possess distinct benefits, such as chemical inertness, a lack of optical blinking, low photobleaching, low cytotoxicity, and excellent biocompatibility, compared with organic dyes and other semiconductor nanodots with heavy metal cores.[1] C-dots are versatile and can be used in a wide range of technologies, such as bioimaging,[2] photocatalysis,[3] sensing,[4] lasers,[5] LED,[6] and energy conversion/storage devices.[7] However, with the exception of promising biological applications, the performance of C-dot-based solid-state luminescent devices is still not satisfactory because strong fluorescence quenching occurs in dry and aggregate states. Only a few cases of high fluorescence in solid-state materials based on C-dots have been reported.[8] At present a lot more research into C-dots is required before they can be used for commercial applications. C-dots can be prepared by several existing techniques, such as laser ablation,[9] pyrolysis,[10] wet oxidation,[11] ultrasound-[12] and microwave-assisted [13] synthesis, hydrothermal synthesis,[14] and electrochemical etching.[15] Among these methods, microwave synthesis has become popular because of the lower associated costs than for the other methods and synthesis is achieved in one step. To achieve luminescent C-dots, surface-passivation reagents are usually required, and the reported quantum yields for C-dots without surface passivation are relatively low (approximately 1%). Qu et al. reported a microwave-assisted one-step method, involving the addition of a tiny amount of an inorganic ion, for the synthesis of luminescent C-dots without surface passivation.[13a] However, the quantum yields of these microwavesynthesized luminescent C-dots are often less than 10%. Herein, we report a simple, low-cost, one-step microwave synthesis route towards water-soluble luminescent C-dots, and their application as a new biocompatible fluorescent ink. First, citric acid (3 g) and urea (3 g) were added to distilled water (10 mL) to form a transparent solution. The solution was then heated in a domestic 750 W microwave oven for 4–5 mins, during which the solution changed from being a colorless liquid to a brown and finally dark-brown clustered solid, indicating the formation of C-dots. This solid was then transferred to a vacuum oven and heated at 608C for 1 h to remove the residual small molecules. An aqueous solution of the C-dots was purified in a centrifuge (3000 rminÀ1, 20 min) to remove large or agglomerated particles. The resulting colored (brown) aqueous solution remained indefinitely stable at various concentrations. The morphology of the C-dots was characterized using transmission electron microscopy (TEM) and atomic force microscopy (AFM). Drops of a dilute aqueous solution of the C-dots were deposited on a carbon-coated copper grid for TEM and on glass and silicon substrates for AFM. The TEM image (Figure 1a) and AFM images with associated height analyses (see the Supporting Information, Figures S6 and S7) illustrate that the C-dots are spherical and well dispersed, and range between 1–5 nm in diameter. The XRD patterns of the C-dots (Figure 1b) displayed two broad peaks centered at 6.8 and 3.4, which are attributed to highly disordered carbon atoms, similar to the graphite lattice spacing.[16] Elemental analysis revealed the composition of the C-dots to be C 41.54 wt%, H 4.41 wt%, N 20.79 wt%, and O (calculated) 33.12 wt%, thus indicating these dots are carbonrich nanodots. The Raman spectra of the C-dots (Figure 1c) display two broad peaks at around 1365 …