Carbon Dots: From Lab Synthesis to Unique Applications

of a dissertation at the University of Miami. Dissertation supervised by Professor Roger M. Leblanc. No. of pages in text. (103) Carbon dots (CDs) have joined the research of carbon-based nanoparticles since 2004. Upon the discovery of carbon dots, CDs were observed to be photoluminescent and small in size (1-10 m). The subsequent broad studies gradually reveal the potential values of CDs. Firstly, CDs have been synthesized with numerous carbon-based precursors including both classic and novel starting materials by various techniques. In this thesis, I will mainly introduce the development of three types of CDs (black CDs, gel-like CDs and orange CDs). Then, considering the lack of careful discussion of purification procedure in many present literatures, I have systematically studied the purification effect of different methods and observed that the selection of purification method should reply on the difference of size, molecular weight, and polarity between precursors and resulting CDs. Besides, the separation of gel-like CDs by TLC or orange CDs by SEC indicates CDs separate fractions are heterogeneous in polarity, molecular weight or size. Characterizations of CDs are often performed with various instruments to reveal their optical, structural and morphological properties. And some other unique properties can be also observed in certain CDs species such as thermal effect in gel-like CDs or solvent effect in orange CDs. In addition, different CDs species in vivo exhibit different properties. Using zebrafish as a model, black CDs species are observed to specially target the bones of zebrafish, which inspires the drug conjugation and delivery of biotin, retinoic acid and gel-like CDs. Furthermore, bloodbrain barrier (BBB) is as obstacle for drug delivery to the central nervous system (CNS). Considering the controllable size, charge, hydrophobicity and surface moiety, different CDs species have been explored for crossing the BBB and have shown the ability to overcome the BBB of zebrafish with different cellular mechanisms. For example, orange CDs have shown the ability to cross the BBB via passive diffusion while CDs prepared from tryptophan cross the BBB by carrier-mediated transport. Additionally, CDs have been widely studied regarding the cytotoxicity with different cell lines and it turned out that CDs are nontoxic regardless of different preparations. Moreover, due to the high photoluminescence, CDs have the potential and have been successfully applied in 2D, 3D printings and cosmetics such as fluorescent hair colorant and nail polish. Among them, 3D printing was first achieved by taking use of the special property of superabsorbent polymer to absorb water to embed orange CDs into superabsorbent polymer. In conclusion, in this thesis, the development of CDs will be illustrated in terms of versatile synthesis, purification, separation, characterization, drug delivery toward bones or across the BBB, printing and cosmetics. However, as a new family member of carbon-based nanoparticles, the studies of CDs have not reached the peak and there are still many properties to be characterized such as photocatalysis and thermoelectricity. Among them, photocatalysis and drug delivery by the conjugation between two CDs species are the focus of my future work.