Graphene Oxide: A Modifiable Platform for Drug Delivery Imaging and Sensing

Abstract

Due to its remarkable electronic properties, graphene has become a basis of many novel microelectronic devices. Its functional derivative, graphene oxide (GO), retains multiple properties of graphene, however, unlike graphene is water soluble and exhibits fluorescence over the functionalization-induced optical band gap. A large graphene platform with oxygen containing groups that can be easily functionalized with active agents or analyte binding sites makes GO attractive for biosensing and drug delivery applications. In addition, an intrinsic GO fluorescence in red/near-infrared region with reduced biological autofluorescence background provides a possibility of fluorescence imaging without the need in additional fluorophores. We explore these properties to develop a multifunctional delivery/imaging/sensing GO platform for cancer therapeutics. GO utilized in our work shows little to no apparent cytotoxicity in concentrations of up to 15 ug/mL. We optimize the size of the commercially available GO flakes via ultrasonic processing for the most efficient cellular internalization and use spectrally-resolved fluorescence imaging for in vitro detection in the spectral range specific to GO emission. Furthermore, ozone processing adding extra oxygen-containing functional groups to GO surface is used to spectrally adjust GO emission and enhance its intensity. Solution-based timed ozone treatment allows to blue shift and increase the intensity of the emission. Concomitantly, such processing provides the basis for versatile covalent functionalization of anticancer agents to the new addends on GO platform via synthetic route akin to peptide synthesis. Optimized GO moieties show efficient intracellular accumulation with a potential preference toward the cancer (MCF-7, HeLa) versus healthy (HEK-293) cells. A pH dependence of GO emission discovered in our previous work provides a sensing mechanism for the acidic environment of cancer cells. In this regard, spectrally-resolved fluorescence microscopy imaging suggests a more blue-shifted GO emission in healthy versus cancer cells. As a result we propose GO as efficient multifunctional candidate for in-vitro delivery of active agents, fluorescence imaging and sensing of cancerous environments.