Graphene Quantum Dots As Effective Formulations for Drug Delivery, Imaging, and Sensing

Abstract

A field of molecular therapeutics has significantly advanced the treatment of many complex conditions, including cancer therapeutics. However many molecular formulations still lack the diagnostic power of tomography-guided approaches, and are restricted by dose-limiting toxicity. Multiple gene therapeutics, which have shown to be effective on a cellular level, require to be delivered in vivo to protect the payload from degradation in blood. This technical gap outlines a clear need for multifunctional delivery/imaging agents. Nanomaterials provide these capabilities, safely delivering therapeutics concomitantly imaging their delivery pathways. Recently graphene derivatives became a focus of intense scientific inquiry including their applications in the biomedical field. However, many issues arise with biocompatibility, degradability and imaging of these platforms. Graphene quantum dots (GQDs) produced via biocompatible bottom-up synthetic route in this work are attractive candidates for bioimaging due to their intrinsic fluorescence in the red/near-infrared spectral region, water solubility, pH mediated response to fluorescence emission, and smaller size for more efficient cellular internalization. We explore these properties to develop a family of graphene-based imaging/sensing/delivery platforms for molecular therapeutics. Our work utilizes three types of GQDs (boron-nitrogen doped, nitrogen doped, and sulfur doped GQDs), which show little to no cytotoxicity quantified via MTT assay up to the maximum imaging concentrations of 1 mg/mL. We use spectrally-resolved fluorescence imaging for in vitro detection in the spectral ranges specific to GQD emission. All GQD types exhibit efficient cellular internalization assessed via their emission within HeLa cells, suggesting a high potential for drug delivery applications and image-guided therapy. A pH dependent emission provides a ratiometric sensing mechanism for the acidic environments of cancer cells; as many cancer cell types excrete lactic acid, their environments are more acidic than those of healthy cells. The difference between fluorescence in healthy (HEK-293)/cancer (HeLa, MCF-7) cell environments is quantified for GQDs in this work via assessing the shifts in emission and/or variations in emission intensities at different wavelengths. As a result we propose GQDs as efficient multifunctional candidates for in vitro delivery of active agents, fluorescence imaging, and pH-sensing of cancerous environments.