Doped Graphene Quantum Dots for Intracellular Multicolor Imaging and Cancer Detection

Abstract

Despite significant advances of nanomedicine, the issues of biocompatibility, accumulation-derived toxicity, and the lack of sensing and in vivo imaging capabilities hamper the translation of most nanocarriers into clinic. To address this, we utilize nitrogen, boron/ nitrogen, and sulfur-doped graphene quantum dots (GQDs) as fully biocompatible multifunctional platforms allowing for multicolor visible/ near-IR imaging and cancer-sensing. These GQDs are scalably produced in one-step synthesis from a single biocompatible glucosamine precursor, are water-soluble, show no cytotoxicity at high concentrations of 1 mg/mL, and demonstrate substantial degradation at 36 h in biological environments as verified by TEM imaging. Because of their small sizes, GQDs exhibit efficient internalization maximized at 12 h followed by further degradation/excretion. Their high-yield intrinsic fluorescence in blue/ green and near-infrared allows for multicolor in vitro imaging on its own or in combination with other fluorophores, and offers the capabilities for in vivo near-IR fluorescence tracking. Additionally, nitrogen-and sulfur-doped GQDs exhibit pH-dependent fluorescence response that is successfully utilized as a sensing mechanism for acidic extracellular environments of cancer cells. It allows for the deterministic, ratiometric spectral discrimination between cancerous (HeLa and MCF-7 cell) versus healthy (HEK-293 cell) environments with substantial intensity ratios of 1.6 to 8. These results suggest fully biocompatible GQDs developed in this work as multifunctional candidates for in vitro delivery of active agents, multicolor visible/near-IR fluorescence imaging, and pH-sensing of cancerous environments.

Synthesis of graphene quantum dots and their applications in drug delivery

“…In order to obtain GQDs with good biocompatibility, sensing and in vivo bioimaging capabilities, Campbell et al [111] used glucosamine-HCl solution as a carbon source and added different dopant precursors (sulfur thiourea or benezeneboronic acid) to synthesize various GQDs, including N-GQDs, NS-GQDs, and BN-GQDs. After the mixed solution was subjected to microwave treatment for 40 min, it was treated with dialysis membranes for 7 days, and GQDs with QY of 15-20% were obtained.…”

Recent Advances on Graphene Quantum Dots for Bioimaging Applications

“…Recently, visible lightemitted S-GQDs have also been used for cellular imaging (Jin et al, 2018). In contrast, Campbell et al reported multicolor emissive S-doped, N-doped, and B,N-co-doped GQDs for both visible and NIR-I imaging in vitro (Campbell et al, 2019). Under different excitation wavelengths, these doped GQDs emitted blue (450 nm), green (535 nm), and red (750 nm) light ( Figure 10A).…”

Rare‐Earth Metal Ions Doped Graphene Quantum Dots for Near‐IR In Vitro/In Vivo/Ex Vivo Imaging Applications

“…They can be utilized for drug/gene delivery while protecting their payload, targeting it to the tissue of interest, and tracing the delivery pathways via a plethora of bioimaging approaches. [1][2][3] As opposed to conventional fluorophores or MRI/CT agents, nanomaterials offer a large modifiable platform for covalent/non-covalent functionalization with biomolecules, [4] generally yield lower toxicity, [5][6][7][8] and offer an expanded and tunable emission spectral range. [9,10] Even though conventional fluorescence markers often have higher quantum yields, [11] the nanomaterial platforms are generally more photostable and, in the long run, provide more quantitative fluorescence tracking and assessment of payload bioavailability.…”

“…However, despite these advantages, the majority of nanomaterials are still restricted from large-scale in vivo applications by complex synthetic routes and high production costs, [17,18] size-dependent [19] /accumulation-derived toxicity, [20] as well as shallow-depth fluorescence imaging in the visible [21,22] suitable mainly for in vitro applications. Very few are biodegradable, [6] nontoxic, [23] or suitable for in vivo imaging or sensing applications [24] without the addition of toxic contrast agents, [25] while few-to-none combine all of these properties. In this work, we aim to generate and examine such multifunctional materials utilizing the capability of functionalized nanoscale systems for near-infrared fluorescence imaging underexplored in current bioimaging technologies due to scarcity of molecular fluorophores exhibiting radiative transitions in that region.…”

“…Biocompatible graphene quantum dots developed recently provide a high promise for bioimaging in the visible and near-infrared. [6,33] These GQDs synthesized by a variety of methods serve as powerful tools for in vitro and in vivo imaging applications, photodynamic therapy, and mRNA detection. [34] GQDs allow for targeted or EPR-driven drug and gene delivery as well as cancer diagnostics, [35] while they are found not to cause any potential toxicity both in vitro and to animal models.…”