Carbon dots (CDs) are the new fellow of carbon family having a size less than 10 nm and attracted much attention of researchers since the last decade because of their unique characteristics, such as inexpensive and facile synthesis methods, easy surface modification, excellent photoluminescence, outstanding water solubility, and low toxicity. Due to these unique characteristics, CDs have been extensively applied in different kind of scientific disciplines. For example in the photocatalytic reactions, drug-gene delivery system, in vitro and in vivo bioimaging, chemical and biological sensing as well as photodynamic and photothermal therapies. Mainly two types of methods are available in the literature to synthesize CDs: the top-down approach, which refers to breaking down a more massive carbon structure into nanoscale particles; the bottom-up approach, which refers to the synthesis of CDs from smaller carbon units (small organic molecules). Many review articles are available in the literature regarding the synthesis and applications of CDs. However, there is no such review article describing the synthesis and complete application of CDs derived from small organic molecules together. In this review, we have summarized the progress of research on CDs regarding its synthesis from small organic molecules (bottom-up approach) via hydrothermal/solvothermal treatment, microwave irradiation, ultrasonic treatment, and thermal decomposition techniques as well as applications in the field of bioimaging, drug/gene delivery system, fluorescence-based sensing, photocatalytic reactions, photo-dynamic therapy (PDT) and photo-thermal (PTT) therapy based on the available literature. Finally, the challenges and future direction of CDs are discussed.

中文翻译：

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小分子衍生碳点：合成及其在传感、催化、成像和生物医学中的应用。

碳点（CD）是尺寸小于10 nm的碳家族的新成员，由于其独特的特性，如廉价且简便的合成方法、易于表面修饰、优异的光致发光、水溶性优异，毒性低。由于这些独特的特性，CD已广泛应用于不同类型的科学学科。例如，在光催化反应、药物基因传递系统、体外和体内生物成像、化学和生物传感以及光动力和光热疗法中。文献中主要有两种类型的方法来合成碳点：自上而下的方法，是将更大质量的碳结构分解成纳米级颗粒；自下而上的方法，是指从较小的碳单元（小有机分子）合成碳点。文献中有许多关于 CD 的合成和应用的评论文章。然而，目前还没有这样的综述文章描述由有机小分子衍生的CD的合成和完整应用。在这篇综述中，我们总结了有机小分子通过水热/溶剂热处理、微波辐射、超声波处理和热分解技术合成碳点（自下而上的方法）的研究进展以及在碳点领域的应用。基于现有文献的生物成像、药物/基因递送系统、基于荧光的传感、光催化反应、光动力疗法（PDT）和光热疗法（PTT）。最后，讨论了CD的挑战和未来方向。