Abstract
We report a simple one-pot microwave assisted “green synthesis” of Graphene Quantum Dots (GQDs) using grape seed extract as a green therapeutic carbon source. These GQDs readily self-assemble, hereafter referred to as “self-assembled” GQDs (sGQDs) in the aqueous medium. The sGQDs enter via caveolae and clathrin-mediated endocytosis and target themselves into cell nucleus within 6–8 h without additional assistance of external capping/targeting agent. The tendency to self-localize themselves into cell nucleus also remains consistent in different cell lines such as L929, HT-1080, MIA PaCa-2, HeLa, and MG-63 cells, thereby serving as a nucleus labelling agent. Furthermore, the sGQDs are highly biocompatible and act as an enhancer in cell proliferation in mouse fibroblasts as confirmed by in vitro wound scratch assay and cell cycle analysis. Also, photoluminescence property of sGQDs (lifetime circa (ca.) 10 ns) was used for optical pH sensing application. The sGQDs show linear, cyclic and reversible trend in its fluorescence intensity between pH 3 and pH 10 (response time: ~1 min, sensitivity −49.96 ± 3.5 mV/pH) thereby serving as a good pH sensing agent. A simple, cost-effective, scalable and green synthetic approach based sGQDs can be used to develop selective organelle labelling, nucleus targeting in theranostics, and optical sensing probes.
Highlights
The photoluminescence property of Graphene Quantum Dots (GQDs) is widely explored in the field of bioimaging and sensing due to their narrow absorption and wide emission spectral characteristics
The extract is a good choice for the self-assembled GQDs (sGQDs) synthesis because being a commercial product; it retains the consistency in the composition which otherwise varies in natural sources due to seasonal variation and geographical location
Field Emission-Gun Transmission Electron Microscopic (FEG-TEM) analysis showed variable size distribution of GQDs based on their dispersion in different solvents (Fig. 2)
Summary
The photoluminescence property of GQDs is widely explored in the field of bioimaging and sensing due to their narrow absorption and wide emission spectral characteristics. Selective nucleus labelling can help to develop advanced and selective active-targeting drug delivery or gene delivery systems[25,26]. These systems as discussed earlier suffer from serious limitations such as photobleaching in organic dyes or cytotoxicity related to semiconductor quantum dots. Some reports have demonstrated fluorescent carbon nanomaterial-based nucleus staining application affecting cell morphology[15,29]. While these reports demonstrated cellular nucleus labelling holistically, we show selective nucleus self-targeting GQDs towards labelling of normal cells within a short time ca. Based on a pH-responsive property of sGQDs, we show a linear fluorescence response to changes in narrow pH (pH 3–10) which can pave a way towards green-synthesis based cheaper and scalable sensing probes in future and have a huge potential in biomedical nanotechnology
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