Graphene quantum dots: Synthesis, optical properties and navigational applications against cancer

Graphene quantum dots (GQDs), zero-dimensional carbon-based nanomaterials, have attracted immense interest for theranostic applications. These applications of GQDs stem from chemical inertness, ultra-small size, and high aqueous dispersibility which probably enable their effective clearance without inflicting toxicity to the host. Relative to heavy metal-based quantum dots and organic fluorophores, GQDs display tunable bandgap and optoelectronic properties. Considerable efforts have been made to modulate their photoluminescence through doping of heteroatoms and controlling the size and edge profile. Subsequent changes in pi-conjugation improve the luminescence stability, signal-to-noise ratio, and imaging depth unachievable with organic dyes. This review covers the synthesis and structural aspects of GQDs in context to their application in cancer diagnosis. After discussing the effect of chemistry (surface functionalization and doping) on optical properties, we present an inclusive view on the sensing of cancer-related biomarkers with GQDs.