Water-soluble Graphene Quantum Dots Research Articles

Recent Breakthroughs in Graphene Quantum Dot-Enhanced Sonodynamic and Photodynamic Therapy

Water-soluble graphene quantum dots (GQDs) have recently exhibited considerable potential for diverse biomedical applications owing to their exceptional optical and chemical properties. However, the pronounced heterogeneity in the composition, size,...

Hydrophilic graphene quantum dots as turn-off fluorescent nanoprobes for toxic heavy metal ions detection in aqueous media

Efforts are being made to develop fast, cost-effective and sensitive sensor to detect water contamination by toxic heavy metal ions. The oxygenated functional groups decorated graphene quantum dots (GQDs) effectively enhances the aqueous solubility and considered as a more desirable and simple sensing material with high sensitivity. Here, photoluminescence (PL) property of GQDs has been employed to devise an optical nanosensor for the detection of toxic heavy metal ions in aqueous media. Hydrothermal method was employed to synthesize highly fluorescent and water soluble GQDs. The fluorescence intensity reduces with the increase in toxic heavy metal ions concentration. The observed PL was analyzed by the Stern-Volmer equation to study the fluorescent quenching mechanism of the system. Nonlinear behavior of Stern-Volmer plot suggests that the reduction in the fluorescent intensity is due to the combination of dynamic and static processes. The fluorescence quenching results showed that, the as synthesized GQDs are an efficient fluorescent probe for heavy metal ions viz. Hg2+, Cd2+ and Pb2+ with the detection limit of 1.171 μM, 2.455 μM and 2.011 μM respectively. This study shows the viability of GQDs as promising material for sensing the heavy metal ions in aqueous solution.

Synthesis of highly fluorescent and water soluble graphene quantum dots for detection of heavy metal ions in aqueous media.

Fluorescent graphene quantum dots (GQDs) are nanomaterials which possess unique properties that show great potential in different applications. In this work, GQDs were synthesized using graphene oxide (GO) as precursor via thermal treatment at high temperature. The obtained GQDs were highly fluorescent and were suitable for the determination of heavy metal ions. X-ray diffraction, FTIR spectroscopy, and UV visible spectroscopy confirm the formation of GQDs. TEM images show that formed GQDs have size ranging from 2 to 10nm. Emission profile of aqueous GQDs was taken by exciting GQDs at different wavelength. The intensity of GQDs remains the same for 4-5months. Furthermore, as prepared, GQDs were used for selective recognition of Fe3+, Pb+2, and Cr3+ from the bunch of different metal ions in aqueous media. Lower limit of detection obtained for Fe3+, Cr3+ and Pb2+ using GQDs were 50, 100 and 100 nM, respectively, which indicatesthat the GQDs canbe utilized as a promising material for sensing of the heavy metal ions. Graphical abstract.

Vanadium coordination compounds loaded on graphene quantum dots (GQDs) exhibit improved pharmaceutical properties and enhanced anti-diabetic effects.

Vanadium compounds are promising anti-diabetic agents, and graphene quantum dots (GQDs) are emerging as potential drug delivery systems to improve drug solubility in water and membrane transport. Using highly dispersible and water-soluble GQDs, we herein prepared a novel GQD-VO (p-dmada) complex, in which vanadium coordination compounds [VO(p-dmada)] were packed closely on one side of the GQD sheets possibly via the π-π stacking mechanism. The in vitro tests showed that GQD-VO(p-dmada) exhibited membrane permeability (Papp) as good as that of GQDs with reduced cytotoxicity. In vivo tests on type 2 diabetic mice demonstrated that GQD-VO(p-dmada) exhibited a delayed glucose lowering profile but more profound effects on insulin enhancement and β-cell protection after three-week treatment compared to VO(p-dmada) alone. In addition, GQD alone was observed for the first time to effectively lower the blood lipid levels of the db/db mice. Overall, GQD-VO(p-dmada) showed improved pharmacokinetic performance and hypoglycemic effects, and using GQD as a nanoplatform for drug delivery may provide vast opportunities for the further design of metal-based pharmaceutical agents.

Water-Soluble Graphene Quantum Dots as High-Performance Water-Based Lubricant Additive for Steel/Steel Contact

In this work, graphene quantum dots (GQDs) were firstly synthesized via a simple hydrothermal route and then its tribological performances as water-based lubricant additive were evaluated for the first time. The morphological observation by transmission electron microscope indicates that uniform and monodispersed GQDs with a mean diameter of about 2 nm can be obtained. Fourier transfer infrared spectroscopy and X-ray photoelectron spectroscopy characterizations demonstrate that there are abundant hydrophilic groups existed on the as-prepared GQDs including hydroxyl, epoxy, and carbonyl groups, endowing GQDs with good dispersibility in water. Moreover, the tribological performances are investigated by optimal-SRV-IV reciprocation friction tester, and the results indicated that both the friction coefficient and the wear rate of water can be largely reduced through adding the appropriate amount of GQDs. As a result, compared with graphene oxide, GQD was more effective to enhance the tribological performances of water at the relatively low concentration. When the concentration of GQDs aqueous dispersion is 4 mg/mL, the corresponding sample of GQDs-4 shows the excellent tribological performances with a 42.5% reduction of friction coefficient and a 58.5% decrease of wear rate compared with those of the water. These promising performances demonstrate that the prepared GQDs can be employed as a novel water-based lubricant additive to greatly enhance the tribological performances of the water.

A simple and green method for the production of nanostructured materials from poly(vinyl alcohol)/graphene quantum dots

Herein, a simple, low-cost and fast approach was proposed to produce fluorescent fibers from the electrospinning of poly (vinyl alcohol)/water-soluble graphene quantum dots (GQDs). Initially, the preparation of GQDs was explored via an easy bottom-up method based on the incomplete carbonization of citric acid under different times (30, 45 and 60 min). Next, fluorescent fibrous mats were prepared from the electrospinning of PVA solutions with different contents of GQDs. These materials were further characterized via several techniques, including High-Resolution Transmission Electronic Microscopy (HRTEM), UV–vis and fluorescence spectroscopies, Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). The GQDs presented a strong blue photoluminescence under UV light exposure. Among the investigated carbonization times, 45 min led to GQDs with the highest fluorescence intensity (regardless the pH) and fluorescence quantum yield (10.5%). HRTEM analysis showed that this carbonization time led to GQDs with uniform and homogeneous dimensions, with an average diameter of 2.5 ± 0.2 nm. After electrospinning, HRTEM revealed a homogeneous distribution of GQDs into the polymeric ultrathin fibers, while increasing the GQDs content in the PVA matrix led to a clear increase in the fluorescence intensity. Interestingly, as the GQDs content increased, a slight red-shift was observed for the maximum of emission, which may be related to light re-adsorption or even as result of Föster Resonance Energy Transfer. This set of results widens the perspectives of application of this low-cost substrate in many fields, via a simple approach using a water-soluble polymer and a naturally occurring component from citrus fruits.

Graphene quantum dots for cancer targeted drug delivery

A biocompatible and cell traceable drug delivery system Graphene Quantum Dots (GQD) based, for the targeted delivery of the DNA intercalating drug doxorubicin (DOX) to cancer cells, is here reported. Highly dispersible and water soluble GQD, synthesized by acidic oxidation and exfoliation of multi-walled carbon nanotubes (MWCNT), were covalently linked to the tumor targeting module biotin (BTN), able to efficiently recognize biotin receptors over-expressed on cancer cells and loaded with DOX. Biological test performed on A549 cells reported a very low toxicity of the synthesized carrier (GQD and GQD-BTN). In GQD-BTN-DOX treated cancer cells, the cytotoxicity was strongly dependent from cell uptake which was greater and delayed after treatment with GQD-BTN-DOX system with respect to what observed for cells treated with the same system lacking of the targeting module BTN (GQD-DOX) or with the free drug alone. A delayed nuclear internalization of the drug is reported, due to the drug detachment from the nanosystem, triggered by the acidic environment of cancer cells.

Detection of α-fetoprotein with an ultrasensitive electrochemiluminescence paper device based on green-luminescent nitrogen-doped graphene quantum dots

A facile one-pot solvothermal method based on exfoliating and disintegrating treatments for graphite oxide was developed to prepare water-soluble graphene quantum dots. Dimethylformamide served as a solvent and source of nitrogen, the as-prepared nitrogen-doped graphene quantum dots (N-GQDs) exhibited bright green emission under ultraviolet irradiation (∼365nm). More importantly, an ultrasensitive paper-based electrochemiluminescence (ECL) immunoassay was developed with green-luminescent N-GQDs as ECL labels and α-fetoprotein antigen (AFP) as model protein. The N-GQDs were promising ECL labels because of their low anodic ECL potential of +0.84V and high biocompatibity, which can facilitate highly sensitive ECL bioassays. A novel paper working electrode was fabricated through a seed-mediated growth approach and served as a promising platform for antibodies attachment. Upon the immunorecognition of the immobilized AFP to its antibody labeled with N-GQDs, the proposed immunoassay displayed increasing ECL intensity, leading to a wide calibration range of 0.005–100ngmL−1 with a detection limit of 1.2pgmL−1 [signal-to-noise ratio (S/N)=3]. The ECL immunoassay for real samples displayed very similar results with the commercial ECL immunoassay, which provided a powerful avenue for the design of the ultrasensitive detection method for clinical application.

Primary hepatocyte imaging by multiphoton luminescent graphene quantum dots.

Water soluble GQDs were systematically characterized as a multiphoton fluorophore and a cell imaging probe. When mouse primary hepatocytes were incubated with GQDs, no significant cytotoxicity was observed up to the treatment concentration of 100 μg ml(-1). Using these GQDs, mouse primary hepatocytes were successfully imaged by multiphoton fluorescence.

Easy extraction of water-soluble graphene quantum dots for light emitting diodes

Graphene quantum dots in powder form obtained in single-step leads fabricating color tunable light emitting diodes with low turn-on voltages.

Immobilizing water-soluble graphene quantum dots with gold nanoparticles for a low potential electrochemiluminescence immunosensor.

Hydrazide-modified graphene quantum dots (HM-GQDs) obtained by refluxing GQDs with hydrazine hydrate were hybridized with gold nanoparticles (AuNPs) through a redox reaction between HM-GQDs and AuCl4(-). The obtained nano-hybrids (HM-GQD-AuNPs) possess the unique electrochemiluminescence (ECL) properties of HM-GQDs and the easy self-assembly with some bio-molecules of AuNPs, which have great potential applications in bio-sensors. HM-GQD-AuNPs were modified on a glassy carbon electrode to develop a novel ECL immunosensor of carcinoembryonic antigen (CEA) as a model target analyte. Due to the increment of electron-transfer resistance after immunoreaction, the ECL intensity decreased as the concentration of CEA was increased. The linear response range was between 0.02 and 80 ng mL(-1), and the detection limit was 0.01 ng mL(-1).

Correction: Easy extraction of water-soluble graphene quantum dots for light emitting diodes

Correction for ‘Easy extraction of water-soluble graphene quantum dots for light emitting diodes’ by Gundam Sandeep Kumar et al., RSC Adv., 2015, 5, 27711–27716.

A novel fluorescent probe involving a graphene quantum dot–enzyme hybrid system for the analysis of hydroquinone in the presence of toxic resorcinol and catechol

An efficient method for the analysis of hydroquinone at trace levels in water samples has been developed in the form of a fluorescent probe based on graphene quantum dots (GQDs). The analytical variable, fluorescence quenching, was generated from the formation of benzoquinone intermediates, which formed during the catalytic oxidation of hydroquinone by horseradish peroxidase (HRP). In general, the reaction mechanism involved hydroquinone, as an electron acceptor, which affected the surface state of GQDs via an electron transfer effect. The water-soluble GQDs were directly prepared by the pyrolysis of citric acid and with the use of the mentioned hybrid enzyme system, the detection limit for hydroquinone was as low as 8.4 × 10−8 M. Furthermore, this analysis was almost unaffected by other phenol and quinine compounds, such as phenol, resorcinol and other quinines, and therefore, the developed GQD method produced satisfactory results for the analysis of hydroquinone in several different lake water samples.

Enhancement in the fluorescence of graphene quantum dots by hydrazine hydrate reduction

A simple and effective chemical method was reported to enhance the fluorescence of graphene quantum dots (GQDs). Specifically, water-soluble GQDs, prepared by solvothermal synthesis from graphene oxide, are chemically reduced by hydrazine hydrate to produce reduced GQDs (rGQDs). The results show that the hydrazine hydrate reduction not only decreases the O/C atomic ratio of GQDs, also changes the bonding type of N atoms. Such surface/edge chemical bond change of GQDs results in that as-made rGQDs exhibit more than two times fluorescence intensity as strong as that of the pristine GQDs.

Electrochemiluminescence of blue-luminescent graphene quantum dots and its application in ultrasensitive aptasensor for adenosine triphosphate detection

A simple approach based on exfoliating and disintegrating treatments for graphite oxide, followed by hydrothermal synthesis, was developed to prepare water-soluble graphene quantum dots (GQDs). The as-prepared GQDs exhibited bright blue emission under ultraviolet irradiation (∼365nm), and showed an excitation-independent photoluminescence feature. More importantly, a newly anodic electrochemiluminescence (ECL) was observed from the water-soluble GQDs with H2O2 as coreactant for the first time, and the ECL induced a strong light emission at a low potential (ca. 0.4V vs. Ag/AgCl). The ECL mechanism is investigated in detail. Employing SiO2 nanospheres as signal carrier, a novel SiO2/GQDs ECL signal amplification labels were synthesized based on which a ultrasensitive ECL aptamer sensor was proposed. Under the optimized experimental conditions, the proposed ECL aptamer sensor exhibited excellent analytical performance for adenosine triphosphate (ATP) determination, ranging from 5.0×10–12 to 5.0×10–9molL−1 with the detection limit of 1.5×10–12molL−1. Due to the low cytotoxicity and excellent biocompatibility, GQDs are demonstrated to be an eco-friendly material as well as excellent ECL labeling agents for biosensor.