Effect Of Graphene Quantum Dots Research Articles

Facilitative effect of graphene quantum dots in MoS2 growth process by chemical vapor deposition**Project supported by the National Basic Research Program of China (Grant Nos. 2016YFA0202300 and 2016YFA0202302), the National Natural Science Foundation of China (Grant Nos. 61527817, 61335006, and 61378073), and the Overseas Expertise Introduction Center for Discipline Innovation, 111 Center, China.

The substrate treatment with seeding promoter can promote the two-dimensional material lateral growth in chemical vapor deposition (CVD) process. Herein, graphene quantum dots (GQDs) as a novel seeding promoter were used to obtain uniform large-area MoS2 monolayer. The obtained monolayer MoS2 films were confirmed by optical microscope, scanning electron microscope, Raman and photoluminescence spectra. Raman mapping revealed that the MoS2 monolayer was largely homogeneous.

Control of the Charge Carrier Concentration and Hall Mobility in PEDOT:PSS Thermoelectric Films

We investigated the effect of graphene quantum dots (GQDs) on the thermoelectric properties of free‐standing poly(3,4‐ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films. The electrical conductivity and Seebeck coefficient of the film containing 0.50 vol% GQDs are 164.60 S/cm and 34.85 μV/K, compared with 22.50 S/cm and 27.72 μV/K, respectively, for the pristine PEDOT:PSS film without GQDs. The power factor (PF) increased up to 22.37 μW/mK2, which is ~13 times higher than that (1.73 μW/mK2) of the pristine film through the selective dedoping of PEDOT by the chemical treatment. Thus, the improved PF is due to the optimized charge carrier concentration and increased Hall mobility by the morphological and structural evolution.

New Antimony Selenide/Nickel Oxide Photocathode Boosts the Efficiency of Graphene Quantum-Dot Co-Sensitized Solar Cells.

A novel assembly of a photocathode and a photoanode is investigated to explore their complementary effects in enhancing the photovoltaic performance of a quantum-dot solar cell (QDSC). While p-type nickel oxide (NiO) has been used previously, antimony selenide (Sb2Se3) has not been used in a QDSC, especially as a component of a counter electrode (CE) architecture that doubles as the photocathode. Here, near-infrared (NIR) light-absorbing Sb2Se3 nanoparticles (NPs) coated over electrodeposited NiO nanofibers on a carbon (C) fabric substrate was employed as the highly efficient photocathode. Quasi-spherical Sb2Se3 NPs, with a band gap of 1.13 eV, upon illumination, release photoexcited electrons in addition to other charge carriers at the CE to further enhance the reduction of the oxidized polysulfide. The p-type conducting behavior of Sb2Se3, coupled with a work function at 4.63 eV, also facilitates electron injection to polysulfide. The effect of graphene quantum dots (GQDs) as co-sensitizers as well as electron conduits is also investigated in which a TiO2/CdS/GQDs photoanode structure in combination with a C-fabric CE delivered a power-conversion efficiency (PCE) of 5.28%, which is a vast improvement over the 4.23% that is obtained by using a TiO2/CdS photoanode (without GQDs) with the same CE. GQDs, due to a superior conductance, impact efficiency more than Sb2Se3 NPs do. The best PCE of a TiO2/CdS/GQDs-nS2-/Sn2--Sb2Se3/NiO/C-fabric cell is 5.96% (0.11 cm2 area), which, when replicated on a smaller area of 0.06 cm2, is seen to increase dramatically to 7.19%. The cell is also tested for 6 h of continuous irradiance. The rationalization for the channelized photogenerated electron movement, which augments the cell performance, is furnished in detail in these studies.

Characterization and physicochemical studies of the conjugates of graphene quantum dots with differently charged zinc phthalocyanines

Unsubstituted zinc phthalocyanine (ZnPc), 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]-phthalocyanine (ZnTPPcQ) and Zn tetrasulfo phthalocyanine (ZnTSPc) were non-covalently (electrostatic and/or π–π interaction) attached to graphene quantum dots (GQDs) to form GQDs-Pc nanoconjugates. Relative to Pcs alone, the presence of GQDs improved the triplet quantum yields with the following values: GQDs-ZnPc (0.73), GQDs-ZnTPPcQ (0.76) and GQDs-ZnTSPc (0.67). Respective Förster resonance energy transfer (FRET) efficiencies were calculated to be 0.81, 0.80 and 0.28. However, singlet oxygen generating abilities of the as-synthesized nanoconjugates were relatively low due to the screening effect of GQDs and quenching in water. This study shows that, the type of Pc, loading and solvent used are among the vital properties to consider when constructing GQD-nanoconjugate systems with optimal triplet quantum yield properties and investigation of their physicochemical properties.

Graphene quantum dots/bisulfite assisted chemiluminescence of rhodamine B-H2O2 system for sensitive recognition of HCHO

A novel and powerful chemiluminescence (CL) system was developed based on the promoting effect of graphene quantum dots (GQDs)/bisulfite on rhodamine B (RB)-H2O2 CL reaction. GQDs were synthesized by a simple, green and affordable approach and characterized using their distinctive absorption and emission patterns. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) transmission and transmission electron microscopy (TEM) analysis were implemented for complementary studies on the structural and morphological characteristics of GQDs. The simultaneous enhancing effect of the synthesized GQDs and bisulfite on the CL emission of RB-H2O2 reaction provided a more strong and efficient CL system. The mechanism of CL emission was described. Furthermore, HCHO as a well-known pollutant, could selectively diminish the developed CL system. This effect was linearly proportional to HCHO concentration which turned the introduced CL system to a susceptible chemosensor for HCHO. Under the optimized operational condition, the linear changing of CL response was obtained in HCHO concentration ranges of 0.02–5μgL−1 and 5–11μgL−1, with limit of detection (LOD) and quantification (LOQ) of 6ngL−1 and 20ngL−1, respectively. Ultimately, presented CL chemosensor was served as an accurate tool for determination of formaldehyde concentration in water and wastewater samples.

Synergic effect of graphene quantum dots and room temperature ionic liquid for the fabrication of highly sensitive voltammetric sensor for levodopa determination in the presence of serotonin

Levodopa, one of the prescribed medications in Parkinson disease, is electrochemically determined here. A room temperature ionic liquid/graphene quantum dots (GQDs) modified carbon paste electrode (RTIL-GQDs/CPE) was used for the electrochemical determination of levodopa. The electro-oxidation mechanism of levodopa at RTIL-GQDs/CPE was also studied. The obtained data showed that the electro-oxidation of levodopa at the RTIL-GQDs/CPE is greatly facilitated, which is attributed to high electrical conductivity of GQDs and RTIL. The electrochemical oxidation of levodopa at the RTIL-GQDs/CPE is a two proton–two electron process. The RTIL-GQDs/CPE showed a good electron mediating behavior followed by well separated oxidation signals of levodopa and serotonin. Square wave voltammetric peak current shows a linear relationship corresponds to the concentrations of levodopa in a linear range of 0.05 to 250.0μM with detection limit of 10.0nM. The RTIL-GQDs/CPE shows excellent ability to determination of levodopa in real samples.

A graphene quantum dot-assisted morin–KMnO4 chemiluminescence system for the precise recognition of cypermethrin

A novel and efficient chemiluminescence (CL) probe was developed for cypermethrin (CYPM) based on the sensitizing effect of graphene quantum dots (GQDs) on the morin–KMnO4 CL reaction.

Effects of graphene quantum dots on linear and nonlinear optical behavior of malignant ovarian cells

We investigate linear and nonlinear optical properties of standard human ovarian cancer cells (cell line: A2780cp) in vitro. Cells were treated by graphene quantum dots (GQDs) with two special concentrations. Nontoxicity of GQDs was examined in standard biological viability tests. Cancerous cells were fixed on a glass slide; then, interaction of light with biofilms was studied in linear and nonlinear regimes. Absorption spectra of untreated biofilms and biofilms with two different concentrations of GQDs was studied by UV-visible spectrophotometer. Optical behavior of biofilms in a linear regime of intensity (with low-intensity laser exposure) was reported using a simple optical setup. After that, we compared the attenuation of light in biofilm of cancerous cells with and without GQDs. Nonlinear behavior of these biofilms was investigated by a Z-scan setup using a continued wave He–Ne laser. Results showed that GQDs decreased the extinction coefficient and changed the sign and exact value of the nonlinear refractive index of malignant ovarian cells noticeably. The nonlinear refractive index of studied cells with no GQDs treatment was in the order of 10−8 (cm2/w) with a positive sign. This quantity changed to the same order of magnitude with a negative sign after GQDs treatment. Thus, GQDs can be used for cancer diagnosis under laser irradiation.

A Quasi-Free-Standing Single Layer of a B3N3-Doped Nanographene Molecule Deposited on Au(111) Single Crystals

We investigate the electronic structure of a quasi-free-standing single layer of a B3N3-doped nanographene molecule deposited on Au(111) single crystals. The single layer shows very high orientational order, as well as high chemical and vacuum stability. We demonstrate that the borazine doping is an alternative way to design a material having electronic properties similar to doped graphene/h-BN. Specifically, borazine doping of nanographenes leads to tuning the gap in the same energy range of carbon-doped h-BN, in agreement with the expected doping effect of graphene quantum dots in h-BN. We support our experimental findings by first-principles calculations.

Graphene Quantum Dots: Effects of Graphene Quantum Dots on the Self‐Renewal and Differentiation of Mesenchymal Stem Cells (Adv. Healthcare Mater. 6/2016)

Graphene Quantum Dots: Effects of Graphene Quantum Dots on the Self‐Renewal and Differentiation of Mesenchymal Stem Cells (Adv. Healthcare Mater. 6/2016)

Effects of Graphene Quantum Dots on the Self-Renewal and Differentiation of Mesenchymal Stem Cells.

The influence of graphene quantum dots (GQDs) on key characteristics of bone marrow derived mesenchymal stem cells (MSCs) phenotype (i.e., self-renewal, differentiation potential, and pluripotency) is systematically investigated in this work. First, the viability and impact of GQDs on the self-renewal potential of MSCs is evaluated in order to determine a threshold for the exposing dose. Second, GQDs uptake by MSCs is confirmed due to the excellent fluorescent properties of the particles. They exhibit a homogenous cytoplasmatic distribution that increases with the time and concentration. Third, the impact of GQDs on the osteogenic differentiation of MSCs is deeply characterized. An enhanced activity of alkaline phosphatase promoted by GQDs indicates early activation of osteogenesis. This is also confirmed upon GQD-induced up-regulation of phenotypically related osteogenic genes (Runx2, osteopontin, and osteocalcin) and specific biomarkers expression (osteopontin and osteocalcin). GQDs also effectively enhance the formation of calcium-rich deposits characteristics of osteoblasts. Furthermore, genes microarray results indicate that the enhanced osteogenic differentiation of MSCs by GQDs is in progress through a bone morphogenetic protein and transforming growth factor-β relative signaling pathways. Finally, intracytoplasmatic lipid detection shows that GQDs can also promote the adipogenic differentiation of MSCs, thus confirming the prevalence of their pluripotency potential.

Particle Size-Dependent Antibacterial Activity and Murine Cell Cytotoxicity Induced by Graphene Oxide Nanomaterials

Recent studies have indicated that graphene and its derivative graphene oxide (GO) engage in a wide range of antibacterial activities with limited toxicity to human cells. Here, we systematically evaluate the dependence of GO toxicity on the size of the nanoparticles used in treatments: we compare the cytotoxic effects of graphene quantum dots (GQDs, <15 nm), small GOs (SGOs, 50–200 nm), and large GOs (LGOs, 0.5–3 μm). We synthesize the results of bacterial colony count assays and SEM-based observations of morphological changes to assess the antibacterial properties that these GOs bring into effect againstE. coli. We also use Live/Dead assays and morphological analysis to investigate changes to mammalian (Murine macrophage-like Raw 264.7) cells induced by the presence of the various GO particle types. Our results demonstrate that LGOs, SGOs, and GQDs possess antibacterial activities and cause mammalian cell cytotoxicity at descending levels of potency. Placing our observations in the context of previous simulation results, we suggest that both the lateral size and surface area of GO particles contribute to cytotoxic effects. We hope that the size dependence elucidated here provides a useful schematic for tuning GO-cell interactions in biomedical applications.

Enhancement of light emission in GaAs epilayers with graphene quantum dots

The effect of graphene quantum dots (GQDs) on the enhancement of PL in GaAs epilayers has been demonstrated and interpreted by carrier transfer due to the work function difference.

Size and refinement edge-shape effects of graphene quantum dots on UV–visible absorption

Using the ab initio density-functional theory method, we calculated the size effect and edge shape effect on UV–visible light absorption of different shapes of graphene quantum dots (GQDs). There are two interesting findings in this study. First, the edge shape effect increase with increasing the size of square GQDs. Second, the Seam atoms, located at the boundary between zigzag and armchair edges, hardly contribute to the strongest visible light absorption. This refinement of the edge-shape effect can be found in rectangular, triangular and hexagonal GQDs. This new finding will be useful in applications of GQDs in the visible light absorption nanodevices.

Visible light photoelectrochemical sensor for ultrasensitive determination of dopamine based on synergistic effect of graphene quantum dots and TiO2 nanoparticles

We have demonstrated a facile approach for fabricating graphene quantum dots–TiO2 (GQDs–TiO2) nanocomposites by a simple physical adsorption method. Compared with pure GQDs and TiO2 nanoparticles (NPs), the as-prepared GQDs–TiO2 nanocomposites showed enhanced photoelectrochemical (PEC) signal under visible-light irradiation. The photocurrent of GQDs–TiO2/GCE was nearly 30-fold and 12-fold enhancement than that of GQDs/GCE and TiO2/GCE, respectively, which was attributed to the synergistic amplification between TiO2 NPs and GQDs. More interestingly, the photocurrent of GQDs–TiO2 nanocomposites was selectively sensitized by dopamine (DA), and enhanced with the increasing of DA concentration. Further, a new PEC methodology for ultrasensitive determination of DA was developed, which showed linearly enhanced photocurrent by increasing the DA concentration from 0.02 to 105μM with a detection limit of 6.7nM (S/N=3) under optimized conditions. This strategy opens up a new avenue for the application of GQDs-based nanocomposites in the field of PEC sensing and monitoring.

Photodynamic antibacterial effect of graphene quantum dots

Synthesis of new antibacterial agents is becoming increasingly important in light of the emerging antibiotic resistance. In the present study we report that electrochemically produced graphene quantum dots (GQD), a new class of carbon nanoparticles, generate reactive oxygen species when photoexcited (470 nm, 1 W), and kill two strains of pathogenic bacteria, methicillin-resistant Staphylococcus aureus and Escherichia coli. Bacterial killing was demonstrated by the reduction in number of bacterial colonies in a standard plate count method, the increase in propidium iodide uptake confirming the cell membrane damage, as well as by morphological defects visualized by atomic force microscopy. The induction of oxidative stress in bacteria exposed to photoexcited GQD was confirmed by staining with a redox-sensitive fluorochrome dihydrorhodamine 123. Neither GQD nor light exposure alone were able to cause oxidative stress and reduce the viability of bacteria. Importantly, mouse spleen cells were markedly less sensitive in the same experimental conditions, thus indicating a fairly selective antibacterial photodynamic action of GQD.

Superior fast switching of liquid crystal devices using graphene quantum dots

We report the doping effect of graphene quantum dots (QDs) in a nematic liquid crystal (NLC) device. The use of graphene QDs leads to improved electro-optical (EO) properties, such as faster response times and a decreased threshold voltage. A 14.8% reduction in the threshold voltage (3.165 V), a 30% decrease in the falling time (4.9 ms) and a 63.6% decrease in the rising time (2.4 ms) were observed for twisted nematic (TN) LC devices (LCDs) that were doped with QDs. We confirm that the doping of the TN-LCD with graphene QDs reduces the field-screening effect, which is caused by impurity ions, whereas the other properties of conventional TN-LCDs are maintained.

그라핀 양자점을 도핑한 TN 셀의 고속 스위칭 특성

In this study, we report the doping effect of graphene quantum dots (QDs) in nematic liquid crystal (NLC) system on rubbed polyimide (PI) surface. The good LC alignment and high thermal stability in QD-LC cell system on rubbed PI surfaces can be measured. Also, the low threshold voltage of QD-TN cell was observed about 2.77 V. The fast response time of 13.2 ms for QD-TN cell can be achieved. Finally, the good voltage holding ratio of QD-TN cell on rubbed PI surface was measured.

Effect of graphene quantum dots on intestinal imaging and mesenteric microcirculation in mice

Objective To study the effect of graphene quantum dots(GQDs)on intestinal image formation and mesenteric microcirculation in mice.Methods The effect of GQDs on intestinal image formation was observed using FX-in vivo imaging system in C57BL/6N mice by comparing with X-ray barium meal examination.Pure water was used as negative control and CdTe QDs was used as positive control.The effects of GQDs on the mesenteric arterioles,venules,and capillaries were observed by the mesenteric microcirculation microscope.Results The mouse intestine took on a bright green image under ultraviolet stimulation 1hafter receiving gavage with GQDs,with clear edge and mucosal structure;meanwhile,mesenteric vessels were in clear light green in the mice.High-density images of the small intestine were observed by X-ray in barium meal examination,but the intestinal mucosal structure was not clear,and the mesenteric vessels were not displayed.The diameter of small arteries in GQDs group was greater and that in the barium meal group was smaller than that before gavage.GQDs,CdTe QDs and barium meal had no notable impact on mouse mesenteric venules.The velocities of blood flow in mesenteric arterioles,venules and capillaries were increased after the administration of barium meal or CdTe QDs,and there were no significant changes in GQDs group.Conclusion GQDs is superior to barium meal in image formation of mouse intestinal wall,and it has less influence on mouse mesenteric microcirculation.

Insight into the Cellular Internalization and Cytotoxicity of Graphene Quantum Dots

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.