Photoluminescent Theranostic Graphene Quantum Dots as a Smart Nanovector for Targeted Drug Delivery

Cancer as a leading cause of human death has attracted substantial research interest in the past several decades. The incidence and mortality of cancer across the world is growing. In 2018, there were almost 18 million new cases of cancer diagnosed, along with 9.6 million deaths. Chemotherapy is one of the major treatment options for cancer. However, conventional chemotherapy using solo anticancer drugs suffers from several limitations, such as low water solubility, poor bioavailability, nonspecific selectivity, low local therapeutic concentration as well as adverse side effects to normal cells. Graphene quantum dots (GQDs), a new kind of nanomaterial with the combined properties of graphene and QDs are considered as natural candidate for effective anti-cancer drug delivery. The high specific surface area and biocompatibility endows their capability to load drugs efficiently with lower toxicity. Also, due to the Photoluminescence property of GQDs, the delivery complex can be observed without further modifying them with other marker dyes. Graphene oxide (GO) and its derivatives have also shown considerable potential in biological applications, including molecular imaging, drug delivery, and photothermal therapy due to their hydrophilicity and biocompatibility. GO exhibits an excellent loading capacity for highly aromatic molecules via strong π- π stacking interactions, which has been employed to deliver various types of water-insoluble drugs into cells. In this study, Graphene Quantum Dots (GQD) have been synthesized from the graphene oxide by chemical oxidation method. Synthesised GQDs showed excitation-dependent Photoluminescence, which is due to surface energy traps and the quantum effect. The quantum effect is related to particle size and causes green fluorescence. It was reported that excitation- dependent emission is due to different energy levels incorporated into the GQDs by different surface groups such as C-O, C=O, O=C-OH. PL showed excitation- dependent passivation of the GQDs reduced the energy ...