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Multidrug resistance (MDR) is the major factor in the failure of many forms of chemotherapy, mostly due to the increased efflux of anticancer drugs that mediated by ATP-binding cassette (ABC) transporters. Therefore, inhibiting ABC transporters is one of effective methods of overcoming MDR. However, high enrichment of ABC transporters in cells and their broad substrate spectra made to circumvent MDR are almost insurmountable by a single specific ABC transporter inhibitor. Here, this study demonstrates that graphene quantum dots (GQDs) could downregulate the expressions of P-glycoprotein, multidrug resistance protein MRP1, and breast cancer resistance protein genes via interacting with C-rich regions of their promoters. This is the first example that a single reagent could suppress multiple MDR genes, suggesting that it will be possible to target multiple ABC transporters simultaneously with a single reagent. The inhibitory ability of the GQDs to these drug-resistant genes is validated further by reversing the doxorubicin resistance of MCF-7/ADR cells. Notably, GQDs have superb chemical and physical properties, unique structure, low toxicity, and high biocompatibility; hence, their capability of inhibiting multiple drug-resistant genes holds great potential in cancer therapy., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Using assistant reagents to improve the pharmaceutical performance of cisplatin (CDDP) has been one of promising strategies. Owing to their extraordinary properties, graphene quantum dots (GQDs) have shown great potentials in biomedical applications. Here we demonstrate that the combination of GQDs with CDDP can effectively enhance the cytotoxicity, cell cycle arrest, and DNA fragmentation that induced by CDDP. We also found that the GQDs improved the interaction of CDDP with DNA. Combing these results with our previous finding that graphene oxide could enhance the permeability of the cells, we believe GQDs improve the pharmaceutical performance of CDDP via first increasing its cellular uptake through improving the cell permeability, and then reinforcing its interaction with DNA once it is inside cells. The remarkable enhancement to CDDP cellular uptake in CDDP resistant cells further specifies that GQDs can increase chemotherapy efficacy of anticancer drugs that are suboptimal due to the drug resistance., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Well-defined graphene quantum dots (GQDs) are crucial for their biological applications and the construction of nanoscaled optoelectronic and electronic devices. However, as-synthesized GQDs reported in many works assume a very wide lateral size distribution; thus, their apparent properties cannot truthfully reflect intrinsic properties of the well-defined GQDs, and more importantly, the applications of GQDs will be affected and limited as well. In this work, we demonstrated that different sized GQDs with a narrow size distribution could be obtained via gel electrophoresis of the crude GQDs prepared through a photo-Fenton reaction of graphene oxide (GO). It is illustrated that the photoluminesce (PL) emissions of the well-defined GQDs originated mainly from the peripheral carboxylic groups and conjugated carbon backbone planes through fluorescence and UV-vis spectroscopies. More importantly, our findings challenge the notion that the excitation wavelength dependent PL property of the as-synthesized GQDs is the intrinsic property of the size-defined GQDs. Preliminary data at the cellular level indicated that the small sized GQDs exhibit weaker quenching DNA dye ability but higher toxicity to the cells compared to that of the as-synthesized GQDs. This discovery is essential to explore applications of the GQDs in pharmaceutics and to understand the origin of the optoelectronic properties of GQDs.

Veratryl alcohol can be oxidized to veratryl aldehyde or veratric acid with excellent selectivity and efficient conversion under acidic and alkaline conditions using Au nanoparticles and graphene quantum dot composites (Au/GQDs) as catalysts.

Graphene quantum dots (GQDs), owing to their unique morphology, ultra-small lateral sizes, and exceptional properties, hold great promise for many applications, especially in the biomedical field. In this work, the cellular internalization, distribution, and cytotoxicity of the GQDs are explored complementarily using transmission electron microscopy, confocal laser scanning microscopy, UV-vis, and fluorescence spectroscopies, and flow cytometry with human gastric cancer MGC-803 and breast cancer MCF-7 cells. It is demonstrated that the GQDs are internalized primarily through caveolae-mediated endocytosis. The effects of GQDs on the cell viability, internal cellular reactive oxygen species (ROS) level, mitochondrial membranes potential, and cell cycles show that the cytotoxicity of GQDs is lower than that of the micrometer-sized graphene oxide (GO). The low cytotoxicity and size consistence render GQDs appropriate for biomedical application., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Graphene quantum dots (GQDs) maintain the intrinsic layered structural motif of graphene but with smaller lateral size and abundant periphery carboxylic groups, and are more compatible with biological system, thus are promising nanomaterials for therapeutic applications. Here we show that GQDs have a superb ability in drug delivery and anti-cancer activity boost without any pre-modification due to their unique structural properties. They could efficiently deliver doxorubicin (DOX) to the nucleus through DOX/GQD conjugates, because the conjugates assume different cellular and nuclear internalization pathways comparing to free DOX. Also, the conjugates could enhance DNA cleavage activity of DOX markedly. This enhancement combining with efficient nuclear delivery improved cytotoxicity of DOX dramatically. Furthermore, the DOX/GQD conjugates could also increase the nuclear uptake and cytotoxicity of DOX to drug-resistant cancer cells indicating that the conjugates may be capable to increase chemotherapy efficacy of anti-cancer drugs that are suboptimal due to the drug resistance.

This minireview describes recent progress in solution-processable graphene quantum dots (SGQDs). Advances in the preparation, modification, properties, and applications of SGQDs are highlighted in detail. As one of emerging nanostructured materials, possible ongoing research related to the precise control of the lateral size, edge structure and surface functionality; the manipulation and characterization; the relationship between the properties and structure; and interfaces with biological systems of SGQDs have been speculated upon., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Due to the high peroxidase-like activity and small lateral size of graphene quantum dots (GQDs), the covalently assembled GQDs/Au electrode exhibits great performance and stability in H(2)O(2) detection. It is better or comparable to some enzyme-immobilized electrodes, and thus could be useful in sensing H(2)O(2) changes in biological systems.

DNA i-motif structures have been found in telomeric, centromeric DNA and many in the promoter region of oncogenes; thus they might be attractive targets for gene-regulation processes and anticancer therapeutics. We demonstrate in this work that i-motif structures can be stabilized by graphene quantum dots (GQDs) under acidic conditions, and more importantly GQDs can promote the formation of the i-motif structure under alkaline or physiological conditions. We illustrate that the GQDs stabilize the i-motif structure through end-stacking of the bases at its loop regions, thus reducing its solvent-accessible area. Under physiological or alkaline conditions, the end-stacking of GQDs on the unfolded structure shifts the equilibrium between the i-motif and unfolded structure toward the i-motif structure, thus promoting its formation. The possibility of fine-tuning the stability of the i-motif and inducing its formation would make GQDs useful in gene regulation and oligonucleotide-based therapeutics.

Graphene quantum dots (GQDs) are great promising in various applications owing to the quantum confinement and edge effects in addition to their intrinsic properties of graphene, but the preparation of the GQDs in bulk scale is challenging. We demonstrated in this work that the micrometer sized graphene oxide (GO) sheets could react with Fenton reagent (Fe(2+)/Fe(3+)/H(2)O(2)) efficiently under an UV irradiation, and, as a result, the GQDs with periphery carboxylic groups could be generated with mass scale production. Through a variety of techniques including atomic force microscopy, X-ray photoelectron spectroscopy, gas chromatography, ultraperformance liquid chromatography-mass spectrometry, and total organic carbon measurement, the mechanism of the photo-Fenton reaction of GO was elucidated. The photo-Fenton reaction of GO was initiated at the carbon atoms connected with the oxygen containing groups, and C-C bonds were broken subsequently, therefore, the reaction rate depends strongly on the oxidization extent of the GO. Given the simple and efficient nature of the photo-Fenton reaction of GO, this method should provide a new strategy to prepare GQDs in mass scale. As a proof-of-concept experiment, the novel DNA cleavage system using as-generated GQDs was constructed.

Recent work has revealed that the lateral size of graphene quantum dots (GQDs) is a crucial factor dictating their biomedical applications. A facile method to sort as-prepared GQDs with wide size distributions into different sized GQDs with narrow size distributions by using aluminum ions was developed. The mechanism of this separation was investigated. The obtained differently sized GQDs were found to exhibit dissimilar cytotoxicity, which suggests that their effects on cells or organisms could be different. [ABSTRACT FROM AUTHOR]

Graphene quantum dots (GQDs), inheriting the superb property of graphene oxide, possess smaller lateral size and high biocompatibility, thus having potential in biomedical applications. We previously discovered that GQDs, combining with Cu2+ions, could cleave DNA primarily through an oxidative pathway; yet, oxidative DNA cleavage is not practically preferred in biology. In this work, we explore the DNA cleavage ability of GQDs with Zn2+and Ni2+. Zn2+and Ni2+alone are incapable of cleaving supercoiled DNA, but when combining with the GQDs, Zn2+and Ni2+exhibit DNA cleavage activity. However, the activity of these two systems is much lower than that of GQDs/Cu2+, and GQDs/Ni2+is less active than GQDs/Zn2+. The functional mechanism of GQDs/Ni2+and GQDs/Zn2+is different from that of GQDs/Cu2+. The GQDs play a key role in the two systems; the redox inactive Zn2+and Ni2+ions assist to generate the oxidative species that eventually lead to the DNA cleavage. The current results together with our previous result indicate that GQDs together with metal ions can cleave supercoiled DNA, and their cleavage activities depend on the properties of metal ions: for redox active metal ions, metal ions play key roles, for redox inactive metal ions, GQDs are dominant. [ABSTRACT FROM PUBLISHER]

Using assistant reagents to improve the pharmaceutical performance of cisplatin (CDDP) has been one of promising strategies. Owing to their extraordinary properties, graphene quantum dots (GQDs) have shown great potentials in biomedical applications. Here we demonstrate that the combination of GQDs with CDDP can effectively enhance the cytotoxicity, cell cycle arrest, and DNA fragmentation that induced by CDDP. We also found that the GQDs improved the interaction of CDDP with DNA. Combing these results with our previous finding that graphene oxide could enhance the permeability of the cells, we believe GQDs improve the pharmaceutical performance of CDDP via first increasing its cellular uptake through improving the cell permeability, and then reinforcing its interaction with DNA once it is inside cells. The remarkable enhancement to CDDP cellular uptake in CDDP resistant cells further specifies that GQDs can increase chemotherapy efficacy of anticancer drugs that are suboptimal due to the drug resistance. [ABSTRACT FROM AUTHOR]

Nanocomposites of graphene quantum dots and Au nanoparticles (GQDs/Au) are immobilized on the Fe 3 O 4 nanoparticles, forming GQDs/Au/Fe 3 O 4 ternary composites. The as-prepared ternary composites exhibit superparamagnetic property rendering them easy to be isolated from the reaction mixture. More importantly, they show superb catalytic activity for solvent-free oxidation of VA and other alcohols that contain an aromatic benzyl group, to the corresponding aldehydes exclusively with air as oxidant. The great stability and selectivity of the GQDs/Au/Fe 3 O 4 indicate that they might be applicable catalysts for the oxidation of aromatic alcohols. [ABSTRACT FROM AUTHOR]