Abstract
Graphene oxide (GO), the most common derivative of graphene, is an exceptional nanomaterial that possesses multiple physical properties critical for biomedical applications. GO exhibits pH-dependent fluorescence emission in the visible/near-infrared, providing a possibility of molecular imaging and pH-sensing. It is also water soluble and has a substantial platform for functionalization, allowing for the delivery of multiple therapeutics. GO physical properties are modified to enhance cellular internalization, producing fluorescent nanoflakes with low (<15%) cytotoxicity at the imaging concentrations of 15 μg/mL. As a result, at lower flake sizes GO rapidly internalizes into HeLa cells with the following 70% fluorescence based clearance at 24 h, assessed by its characteristic emission in red/near-IR. pH-dependence of GO emission is utilized to provide the sensing of acidic extracellular environments of cancer cells. The results demonstrate diminishing green/red (550/630 nm) fluorescence intensity ratios for HeLa and MCF-7 cancer cells in comparison to HEK-293 healthy cells suggesting a potential use of GO as a non-invasive optical sensor for cancer microenvironments. The results of this work demonstrate the potential of GO as a novel multifunctional platform for therapeutic delivery, biological imaging and cancer sensing.
Highlights
Graphene oxide is proposed as a prospective platform for therapeutics, as unlike other therapeutic nanoformulations, it can be produced at low cost and large quantities, functionalized with therapeutics, and exhibits pH-dependent fluorescence in the red/near-IR spectral region with reduced biological autofluorescence background and tissue scattering
Individual Graphene oxide (GO) flakes can be readily seen in aqueous suspensions (Fig. S1). 480 nm excitation is used throughout this work, while detecting GO emission in red (630 nm) and green (550 nm) to achieve imaging and pH sensing of cancer cell environments
Microscopy images of GO-treated HeLa cells washed prior to imaging to remove any extracellular GO adhering to the cell membrane, indicate substantial 630 nm emission from nanoscale GO flakes inside the cells with no apparent autofluorescence in control HeLa cells (Fig. 1a,b)
Summary
The potential to perform multiple functions using one agent is the attractive force driving the integration of molecular cancer therapeutics with nanomaterials-based drug-delivery vehicle systems[29]. Many such nanoformulations are currently used for drug transport and imaging[30,31,32], few possess concomitant sensing capacity[33,34]. In this work we utilize GO fluorescing in visible/NIR and explore the property of GO to vary its fluorescence as a function of pH41 in the biological range for the detection of such cancerous environments. The feasibility of in-vitro GO optical pH sensing is investigated as a novel multifunctional agent for delivery, imaging and sensing of cancerous environments. The objective of this work is to optimize GO for these applications and test its feasibility in vitro
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