Graphene oxide as selective transporter of flavonols for physiological target DNA: A two-color fluorescence approach

Our study determines the selectivity of graphene oxide (GO) to recognize its ligands (e.g. flavonoids) in facilitating the binding with their respective cellular targets. The polyhydroxy phenolic compounds, flavonoids, have a broad spectrum of therapeutic activities with high potency and low systemic toxicity. Despite the vast medicinal importance, their bioavailability is low. In this exploratory study, GO has been used as the transporter of three flavonols fisetin (3, 7, 3', 4'-OH flavone), quercetin (3, 5, 7, 3', 4'-OH flavone), and morin (3, 5, 7, 2', 4'-OH flavone) for the physiological target DNA. Calf thymus DNA is chosen as the model physiological target. Characterization of GO is performed using FTIR, Raman and dynamic light scattering (DLS) spectroscopy. The strong absorption peak at 1730 cm^-1 indicated the presence of carbonyl groups (C=O) at the edges of GO. The presence of sp³ carbons due to oxidation of sp² carbons in GO is further proved by Raman spectroscopy. DLS provided the average size of the GO particles to be ~9 microm. The dual luminescence behavior of the flavonols has been used in this study for the noninvasive sensing of the GO-flavonol and GO-flavonol-DNA interactions; as well as for the selectivity of GO for one flavonol over other in transferring the ligand to DNA. Furthermore, circular dichroism (CD) indicated that the optical activity of GO undergoes drastic change when conjugated with flavonols. Molecular modeling corroborated the findings from the binding studies. GO provides high promise as facilitators for drug delivery.