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Top2. Fabrication Of Biocompatible Carbon Nanodots As Functional Imaging Agents
The fabrication methods for carbon nanodots with tunable size can generally be classified into two main approaches: bottom-up and top-down (Li, 2012; Zuo, 2015). Top-down preparations of fluorescence C-dots are the early preparation approaches, including arc-discharge method (Li, 2012; Jian, 2010;), electrochemical oxidation (Zheng, 2009; Lu, 2009; Zhou, 2007; Zhao, 2008), and laser ablation (Yang, 2009; Goncalves, 2010). Compared with the multistep preparation method of C-dots, one-step reaction processes not only simplify the preparation procedure, but also these C-dots are with better fluorescent properties. Additionally, thus created C-dots may express special fluorescent properties by using various organic reaction solution. Bottom-up approaches are based on the polymerization reaction for small molecules to the formation of nanoscale C-dots. This strategy includes hydrothermal method (Liu, 2007; Wang, 2013; Qian, 2014; Xu, 2014; Dong, 2014; Gao, 2013; Ray, 2009), microwave-assisted pyrolysis method (Tang, 2014; Zhu, 2009; Wang, 2012; Chandra, 2011; Yang, 2012), ultrasonic method (Oza, 2015), acid dehydration method (Lecroy, 2014), and pyrolysis method (Bourlinos, 2008; Zong, 2014). Among them, the most widely used are the hydrothermal method and microwave-assisted pyrolysis method, which can be realized by the one-step method for preparing fluorescent C-dots with high quantum yield (QY > 50%). Thus, nanoparticles with diameter between 1–2 nm are formed spontaneously in one-step thermal treatment from different organic materials and are sufficiently well characterized by different structural methods. The C-dot hydrophobic core is made of pure carbon (consisted of aromatic domains) that is surrounded by polar (hydroxyl, carboxyl, amino, carbonyl and epoxy) and alkyl surface groups as shown on Figure 1. The organic functional groups make the nanoparticles highly soluble in aqueous media and help their penetration through the cell membrane mainly by endocytosis.