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Early diagnosis of diseases is of great importance because it increases the chance of a cure and significantly reduces treatment costs. Thus, development of rapid, sensitive, and reliable biosensing techniques is essential for the benefits of human life and health. As such, various nanomaterials have been explored to improve performance of biosensors, among which, carbon dots (CDs) have received enormous attention due to their excellent performance. In this Review, the recent advancements of CDbased biosensors have been carefully summarized. First, biosensors are classified according to their sensing strategies, and the role of CDs in these sensors is elaborated in detail. Next, several typical CD-based biosensors (including CD-only, enzymatic, antigen− antibody, and nucleic acid biosensors) and their applications are fully discussed. Last, advantages, challenges, and perspectives on the future trends of CD-based biosensors are highlighted.

Among various cancers, pediatric brain tumors represent the most common cancer type in children and the second most common cause of cancer related deaths. Anticancer drugs and therapies, such as doxorubicin (Dox), have severe side effects on patients during chemotherapy, especially for children as their bodies are still under development. These side effects are believed to be due to the lack of a delivery system with high efficacy and targeting selectivity, resulting in serious damages of normal cells. To improve the efficacy and selectivity, the transferrin (Trans) receptor mediated endocytosis can be utilized for drug delivery system design, as transferrin receptors are expressed on the blood brain barrier (BBB) and often over expressed in brain tumor cells. Carbon dots (C-Dots) have recently emerged as benign nanoparticles in biomedical applications owing to their good water solubility, tunable surface functionalities and excellent biocompatibility. The unique characteristics of C-Dots make them promising candidates for drug delivery development. In this study, carbon dots-transferrin-doxorubicin covalent conjugate (C-Dots-Trans-Dox) was synthesized, characterized by different spectroscopic techniques and investigated for the potential application as a drug delivery system for anticancer drug doxorubicin to treat pediatric brain tumors. Our in vitro results demonstrate greater uptake of the C-Dots-Trans-Dox conjugate compared to Dox alone presumably owing to the high levels of transferrin receptors on these tumor cells. Experiment showed that C-Dots-Trans-Dox at 10 nM was significantly more cytotoxic than Dox alone, reducing viability by 14-45%, across multiple pediatric brain tumor cell lines.