Carbon dots: An updated overview on their synthesis, properties, and applications in pharmaceutical and biomedical sciences

Nowadays, carbon-based materials have acquired more attention in numerous fields including engineering, medicine, and pharmaceutics. As a new class of small carbon nanomaterials, carbon dots are developed due to their excellent physicochemical properties such as spherical shape, non-toxicity, cost effectiveness, facile, biocompatibility, and discrete particles <10 nm in diameter. In 2004, these carbon dots were first discovered accidentally during processing of single walled carbon nanotubes. Carbon dots have created huge excitement due to their advantages such as high water solubility, excellent biocompatibility, and resistance to photo bleaching. Carbon dots show unique properties such as photo stability, low toxicity, fluorescence, photo chemiluminescence, and electrochemiluminescence. Due to these properties, they have a wide range of applications in the field of bioimaging and drug delivery. Carbon dots are classified into two groups: Amorphous based carbon dots and graphene-based quantum dots with sp2 hybridization. The synthesis methods of carbon dots were reviewed along with their advantages and disadvantages. The applications of carbon dots in drug delivery, gene delivery, targeted drug delivery, crossing blood–brain barrier, and bio imaging were discussed.