Carbon dot-based nanomaterials in neurodegeneration: addressing neurobiological barriers and targeting challenges

Neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis, represent a major global health challenge due to their progressive nature and limited therapeutic options. One of the primary obstacles to treating these disorders is the blood-brain barrier (BBB), which restricts the delivery of most therapeutic agents into the central nervous system. In recent years, carbon-based nanomaterials, particularly carbon dot (CD) nanostructures, have emerged as promising platforms for neurological applications owing to their ultrasmall size, BBB-crossing ability, and anti-inflammatory and neuroprotective properties, in addition to tunable surface chemistry, strong photoluminescence, and favorable biocompatibility. This review provides a comprehensive overview of recent research developments in the application of CD-based nanomaterials, including carbon nanodots, carbon quantum dots, graphene quantum dots, and carbon polymer dots, for the potential treatment of neurodegenerative diseases. The synthesis strategies and carbonization approaches used to produce these carbon nanomaterials are discussed, along with their physicochemical properties relevant to neurobiological applications, such as particle size, surface functionalization, heteroatom doping, optical properties, and stability in biological environments. Furthermore, the mechanisms by which CD-based nanomaterials can traverse the BBB are examined, including receptor-mediated and adsorptive-mediated transcytosis pathways. In addition, their applications are discussed, with particular focus on their roles in bioimaging, biosensing, inhibition of pathological protein aggregation, antioxidative activity, and targeted drug delivery. Finally, key challenges related to toxicity, biodistribution, large-scale synthesis, and clinical translation are discussed, along with future perspectives for the development of multifunctional theranostic platforms. Overall, use of CD-based nanomaterials represents a promising emerging strategy for overcoming neurobiological barriers and enabling the development of next-generation nanotherapeutics for the management of neurodegenerative diseases.