Types Of Graphene Quantum Dots Research Articles

Graphene quantum dots–From spectroscopic performance to 3D printing applications and interaction studies with normal and cancer cells

In this study, different types of graphene quantum dots (GQDs) are investigated to understand their spectroscopic properties. Morphological and size analyses were performed. The mechanism of action of radical photopolymerization was evaluated. The obtained materials proved to be useful for developing efficient photoinitiating systems for 3D printing applications. In addition, the cytotoxicity of the GQDs was studied, and their effects on living cells were investigated. We demonstrated that GQDs can not only act as efficient photoinitiators but also as constituents of hydrogels that express very low toxicity and may interact with cells. The latter makes it possible to study them in the future as useful modern biosensors.

Quantitative mixed-valence state identification of metal ions based on fluorescence response of graphene quantum dots

Quantitative identification of mixed-valence metal ions is essential for gaining deeper insights into critical chemical and biological processes in environmental science, chemical engineering, and biological systems. However, a simple approach of quantitative identification mixed-valence metal ions in solution has remained a challenge. In this study, we have experimentally observed a significant linear correlation (R2 = 0.99) between the concentration of high-valence metal ions (using iron ions as an example) and the fluorescence intensity of graphene quantum dots (GQDs). Utilizing the distinct fluorescence responses of GQDs to high-valence and low-valence metal ions, reliable quantitative detection of mixed-valence metal ions has been successfully achieved. Remarkably, we introduced real-time monitoring of mixed-valence metal ions, revealing a shift from a molar ratio of approximately 4.0 to 2.0. Density functional theory calculations have revealed significant differences in charge transfer between high-valence and low-valence states of metal ions adsorbed onto GQDs. Furthermore, the versatility of this method can extend to various types of GQDs and metal ions, highlighting its universal applicability. This work presents a simple, convenient, and cost-effective approach for quantitatively identifying mixed-valence metal ions in solution, offering a new avenue and opportunity for applications in biochemistry, environmental science, catalysis and materials science.

Graphene Quantum Dots Modulate Stress Granule Assembly and Prevent Abnormal Phase Transition of Fused in Sarcoma Protein.

Protein liquid-liquid phase separation (LLPS) plays a crucial role in mediating dynamic assembly of different membraneless organelles such as stress granules (SGs). Dysregulation of dynamic protein LLPS leads to aberrant phase transition and amyloid aggregation which is closely associated with neurodegenerative diseases. In this study, we found that three types of graphene quantum dots (GQDs) exhibit potent activity in preventing SG formation and promoting SG disassembly. We next demonstrate that GQDs can directly interact with the SGs-containing protein fused in sarcoma (FUS), inhibit and reverse FUS LLPS, and prevent its abnormal phase transition. Moreover, GQDs display superior activity in preventing amyloid aggregation of FUS and disaggregating preformed FUS fibrils. Mechanistic study further demonstrates that GQDs with different edge-site exhibit distinct binding affinity to FUS monomers and fibrils, which accounts for their distinct activities in modulating FUS LLPS and fibrillation. Our work reveals the potent capability of GQDs in modulating SG assembly, protein LLPS, and fibrillation and sheds light on rational design of GQDs as effective modulators of protein LLPS for therapeutics application.

Electron transport of chemically treated graphene quantum dots-based dye-sensitized solar cells

The main aim of this work is to elucidate the effect of the chemical treatment of titanium tetrachloride (TiCl4) in graphene quantum dots (GQDs)-based dye-sensitized solar cells (DSSCs). Although this type of chemical treatment has been used in DSSCs, the detailed electron transport properties of TiCl4-treated TiO2/GQDs+dye have not been studied yet. In this study, we have proposed a detailed mechanism for how the extra titania layer with TiCl4 provides high surface area and porosity to improve the adsorption of GQDs and dye. Moreover, the electron transport analysis revealed that the treatment reduced the electron recombination rate and increased the electron injection efficiency up to 73.8%, leading to a high Jsc and longer electron lifetime in the DSSC. Additionally, a performance comparison study with other types of GQDs under TiCl4 treatment was also investigated in this work.

In vivo toxicity assessment of four types of graphene quantum dots (GQDs) using mRNA sequencing

GQDs show great potential in drug carriers, bioimaging, biosensors, theranostics, and are recently reported as promising therapeutic agents to treat amyloid-related diseases such as Parkinson’s disease and inflammations such as colitis. However, current toxicity data about GQDs based on in vivo toxicity assessments remain scarce. In the study, we examined the mRNA expression changes of zebrafish embryos exposed to four types of GQDs, including raw graphene quantum dots (R-GQDs), graphene oxide quantum dots (GOQDs), carboxyl GQDs (C-GQDs), and aminated GQDs (A-GQDs). Firstly, we treated embryos with the four GQDs at three concentrations (50, 100, and 200 μg/mL), and found that only A-GQDs caused embryonic developmental arrest at 100 and 200 μg/mL with significantly decreased survival rates and heartbeat rates, as well as the elevated malformation rates. Next, we analyzed the mRNA sequencing data acquired from zebrafish embryos exposed to the four GQDs for 7 days at 100 μg/mL, and found that all GQDs can act on potassium (K+) and calcium (Ca2+) channels, and spliceosomes with varying degrees of regulatory effects. Compared to other GQDs, A-GQDs can strongly perturb the anticoagulant protein C (PC) pathway via activating most genes associated with complement and coagulation system, cell adhesion molecules (CAMs), and MAPK. In conclusion, this study provided substantial transcriptomic data underlying the common signaling pathways induced by various types of GQDs and pointed out the specific toxicity of A-GQDs on hemostatic system.

Ultra-narrow-bandwidth graphene quantum dots for superresolved spectral and spatial sensing

Narrow-bandwidth luminescent materials are already used in optoelectronic devices, superresolution, lasers, imaging, and sensing. The new-generation carbon fluorescence nanomaterials—carbon dots—have attracted considerable attention due to their advantages, such as simple operation, environmental friendliness, and good photoelectric performance. In this work, two narrower-bandwidth (21 and 30 nm) emission graphene quantum dots with long-wavelength fluorescence were successfully prepared by a one-step method, and their photoluminescence (PL) peaks were at 683 and 667 nm, respectively. These red-emitting graphene quantum dots were characterized by excitation wavelength dependence of the fluorescence lifetimes, and they were successfully applied to spectral and spatial superresolved sensing. Here, we proposed to develop an infrared spectroscopic sensing configuration based on two narrow-bandwidth-emission graphene quantum dots. The advantage of the method used is that spectroscopic information was extracted without using a spectrometer, and two narrow-bandwidth-emission graphene quantum dots were simultaneously excited to achieve spatial separation through the unique temporal “signatures” of the two types of graphene quantum dots. The spatial separation localization errors of the graphene quantum dots (GQDs-Sn and GQDs-OH) were 1 pixel (10 nm) and 3 pixels (30 nm), respectively. The method could also be adjusted for nanoscope-related applications in which spatial superresolved sensing was achieved.

The fine-structure characteristics and isopropanol/water dehydration through pervaporation composite membranes improved with graphene quantum dots

The facile synthesis and functionalization of graphene quantum dots (GQDs) have shown benefits in membrane separation processes since it could augment their performance. Here, the fine-structure characteristics and alcohol dehydration performance of a polymeric pervaporation composite membrane integrated with either nitrogen-doped graphene quantum dots (NGQDs) or oxygen-passivated graphene quantum dots (OGQDs) were evaluated. Calcium ion cross-linked sodium alginate (Alg) was used as the polymer matrix since the multiple hydroxyl and carboxyl groups could form hydrogen bonds with GQDs. The interfacial interaction between the two types of GQDs and Alg was evaluated through the pervaporation dehydration of isopropanol/water (i-PrOH/water) mixture and further analyzed using positron annihilation lifetime spectroscopy (PALS). The PALS results revealed that different functionalized GQDs affect the fine-structure characteristics of Alg matrix and resulted to different alcohol dehydration performance. In dry state, both NGQD and OGQD integrated membranes have smaller free volume spaces than the pristine Alg membrane indicating improved interfacial interaction between the GQD and Alg. However, in wet state, larger free volume spaces appeared and it was shown that OGQD integrated membranes have the largest. These data explained the higher permeation flux and separation factor of Alg-OGQD membranes than Alg-NGQD and Alg. The total flux reached to 5580 g m−2h−1 with a water concentration in permeate of ~99.95% in dehydrating i-PrOH/water (70/30 wt%) at 70 °C for Alg-OGQD membrane with 100 ppm of OGQD (Alg-OGQD100). Furthermore, the membrane remained stable for 720 h of operation at 70 °C with a water concentration in permeate >99% showing potential for practical applications.

Graphene quantum dots as singlet oxygen producer or radical quencher - The matter of functionalization with urea/thiourea.

Due to their low cost and possible green synthesis, high stability and resistance to photobleaching, graphene quantum dots (GQDs) can be considered as one of the class of carbon nanomaterials which may have great potential as an agent for photosensitized oxygen activation. In such a way, GQDs can be used as a theranostic agent in photodynamic therapy. In this work pristine GQDs, GQDs irradiated with gamma rays and GQDs doped with N and N, S atoms are produced using a simple, green approach. By using different techniques (AFM, HR-TEM, SEM-EDS, FTIR, XRD, PL and UV-Vis) we investigated structural and optical properties of the new types of GQDs. We showed that GQDs functionalized with thiourea (GQDs-TU) completely lost the ability to produce singlet oxygen (1O2) upon photoexcitation while functionalization with urea (GQDs-U) improves the capability of GQDs to produce 1O2 upon the same conditions. Thus, presented GQDs modification with urea seems like a promising approach for the production of the efficient photosensitizer. On the opposite, GQDs-TU are efficient OH quencher. Due to high singlet oxygen production and low cytotoxicity below 100 μg/mL against HeLa cells, GQDs-U is a good candidate as an agent in photodynamic therapy at this concentration.

Recycling Oxacillin Residues from Environmental Waste into Graphene Quantum Dots

Of great concern are the residual antibiotics from dirt that can be found in farm soil and wastewater. This kind of emerging pollutant into engineered nanomaterials is riveting. This work proposes the elimination and transformation of a beta-lactam antibiotic, oxacillin, from environmental waste to graphene quantum dots (GQDs). Two protocols were followed in which the use of ethylenediamine (EDA) in the transformation leads to GQDs with excellent optical properties. Therefore, two types of GQDs were synthesized in a Teflon-lined stainless autoclave by a thermal procedure using oxacillin in the absence and presence of EDA. The ensuing e-GQDs from oxacillin and EDA display a stronger fluorescence emission in comparison to those synthesized without EDA (o-GQDs). The combination of Kaiser test analyses, infrared (IR) and Raman measurements revealed the presence of oxygen-containing groups and primary amines at the edges of the graphitic nanolayer for e-GQDs. This straightforward strategy brings hope and opens a new interest in waste recycling by means of extracting residual contaminants from the environment for their further transformation into adequate non-toxic graphitic nanomaterials with potential applications.

Color Sensitive Response of Graphene/Graphene Quantum Dot Phototransistors

We present the fabrication and characterization of all-carbon phototransistors made of graphene three terminal devices, coated with atomically precise graphene quantum dots (GQD). Chemically synthesized GQDs are the light absorbing materials, while the underlying chemical vapor deposition (CVD)-grown graphene layer acts as the charge transporting channel. We investigated three types of GQDs with different sizes and edge structures, having distinct and characteristic optical absorption in the UV–vis range. The photoresponsivity exceeds 106 A/W for vanishingly small incident power (<10–12 W), comparing well with state of the art sensitized graphene photodetectors. More importantly, the photoresponse is determined by the specific absorption spectrum of each GQD, exhibiting the maximal responsivity at the wavelengths corresponding to the absorption maxima. Overall this behavior can be ascribed to the efficient and selective absorption of light by the GQDs, followed by a charge transfer to graphene, a mechanis...

Graphene Quantum Dots As Effective Formulations for Drug Delivery, Imaging, and Sensing

A field of molecular therapeutics has significantly advanced the treatment of many complex conditions, including cancer therapeutics. However many molecular formulations still lack the diagnostic power of tomography-guided approaches, and are restricted by dose-limiting toxicity. Multiple gene therapeutics, which have shown to be effective on a cellular level, require to be delivered in vivo to protect the payload from degradation in blood. This technical gap outlines a clear need for multifunctional delivery/imaging agents. Nanomaterials provide these capabilities, safely delivering therapeutics concomitantly imaging their delivery pathways. Recently graphene derivatives became a focus of intense scientific inquiry including their applications in the biomedical field. However, many issues arise with biocompatibility, degradability and imaging of these platforms. Graphene quantum dots (GQDs) produced via biocompatible bottom-up synthetic route in this work are attractive candidates for bioimaging due to their intrinsic fluorescence in the red/near-infrared spectral region, water solubility, pH mediated response to fluorescence emission, and smaller size for more efficient cellular internalization. We explore these properties to develop a family of graphene-based imaging/sensing/delivery platforms for molecular therapeutics. Our work utilizes three types of GQDs (boron-nitrogen doped, nitrogen doped, and sulfur doped GQDs), which show little to no cytotoxicity quantified via MTT assay up to the maximum imaging concentrations of 1 mg/mL. We use spectrally-resolved fluorescence imaging for in vitro detection in the spectral ranges specific to GQD emission. All GQD types exhibit efficient cellular internalization assessed via their emission within HeLa cells, suggesting a high potential for drug delivery applications and image-guided therapy. A pH dependent emission provides a ratiometric sensing mechanism for the acidic environments of cancer cells; as many cancer cell types excrete lactic acid, their environments are more acidic than those of healthy cells. The difference between fluorescence in healthy (HEK-293)/cancer (HeLa, MCF-7) cell environments is quantified for GQDs in this work via assessing the shifts in emission and/or variations in emission intensities at different wavelengths. As a result we propose GQDs as efficient multifunctional candidates for in vitro delivery of active agents, fluorescence imaging, and pH-sensing of cancerous environments.

Nitrogen-doped graphene quantum dots (N-GQDs) perturb redox-sensitive system via the selective inhibition of antioxidant enzyme activities in zebrafish

Graphene quantum dots (GQDs) are well-known for its potential applications for bioimaging, biosensor, and drug carrier in biomedicine. GQDs are well characteristic of intrinsic peroxidase-like catalytic activity, which is proven effective in scavenging the free radicals, such assuperoxide anion, hydrogen peroxide, and hydroxyl radical. GQDs are also well praised for its low in vivo and in vitro toxicity. Here, we found that nitrogen-doped GQDs (N-GQDs) can strongly disturb redox-sensitive system via the selective inhibition of endogenous antioxidant enzyme activities in zebrafish. The enzyme activities or transcription levels of a battery of hemoproteins including catalase (CAT), superoxide dismutase (SOD), respiratory chain complex I, complex Ⅲ, hemoglobin (Hb), and myeloperoxidase (MPO), were significantly suppressed by N-GQDs. We also found that N-GQDs activated the cytochrome P450 monooxygenase (e.g. cyp1a) and the associated aryl-hydrocarbon receptor repressors (ahrr1 and ahrr2) in zebrafish embryos. Compared to the ultrasmall graphene oxide (USGO), N-GQDs exhibited stronger fluorescent permeability and tissue-specific bio-accumulative effects. Taken together, our findings highlighted that exposure to N-GQDs can disrupt endogenous antioxidant enzyme activities, possibly via the competitive inhibition of electron transfer process. Our results in this study provided solid data for biosafety evaluations of various types of GQDs, and created an alert for the future biomedical applications of N-GQDs.

Graphene quantum dots prepared by gaseous detonation toward excellent friction-reducing and antiwear additives

A great deal of research has been focused on the photoluminescence (PL) behaviors of graphene quantum dots (GQDs), but tribological characteristics against GQDs still remain an open issue. Herein, four kinds of powdery GQDs are successfully synthesized via a one-pot gaseous detonation method without any post-treatment or purification. The tribological properties of GQDs serving as lubricant additives for 150SN mineral oil are investigated in detail using a four-ball tester by altering the concentration and types of GQDs. The results demonstrate that GQDs can act as excellent performance additives. In particular, the mean friction coefficient, wear scar diameter and depth of lower balls lubricated by 150SN mineral oil under 392 N correspondingly reduce by 65.2%, 43.5% and 90.9%, when appropriate types of GQDs at optimal additive concentration of 0.8 wt% are introduced. Finally, on the basis of microstructures, compositions and tribological properties of four kinds of GQDs, a reasonable lubricating mechanism of GQDs-based additives is proposed and illustrated that excellent friction-reducing and antiwear properties may be attributed to the synergetic effects, including polishing effect and mending effect.

Mass production of tunable multicolor graphene quantum dots from an energy resource of coke by a one-step electrochemical exfoliation

Herein, we originally propose a simple and facile one-step electrochemical exfoliation approach to synthesize in large scale graphene quantum dots (GQDs) from low-cost energy resource of coke. We found that the GQDs emerged multi-color fluorescence by adjusting the water content of electrolyte solution and applying current density, which effectually caused green-GQDs (G-GQDs), yellow-GQDs (Y-GQDs), and orange-GQDs (O-GQDs) of regular micro-variation in size from 3.02 to 4.61 nm with the fluorescence emissions at 500, 530 and 560 nm, respectively. Furthermore, blue-GQDs (B-GQDs) with emission at 440 nm can be obtained by reducing G-GQDs with NaBH4 at room temperature for 4 h. The quantum yields of B-, G-, Y- and O-GQDs are obtained up to 19.27%, 8.47%, 7.90% and 9.24%, respectively. The B-, G-, Y- and O-GQDs with high yields severally corresponding to 13.04 wt%, 17.88 wt%, 42.86 wt% and 31.13 wt%, possess scalable and industrial production prospect. All four types of GQDs were fully characterized and the electrochemical production mechanism of these GQDs has been also investigated in full. Additionally, GQDs were also available to fabricate their solid-state GQDs/epoxy composites for potential applications in multicolor light-emitting diode devices.

Exploring the Emissive States of Heteroatom-Doped Graphene Quantum Dots

The photoluminescence (PL) emission states of heteroatom-doped graphene quantum dots (GQDs) remain unknown, particularly the assignment of the low-energy excitation band (more than 330 nm). To address these issues, this work synthesized three different types of GQDs: undoped GQDs (UGQDs), nitrogen-doped GQDs (NGQDs), and boron-doped GQDs (BGQDs), with similar sizes, chemical compositions (types and compositions of surface functional groups), and defects using a constant potential electrolysis method. The PL emissive states in these GQDs and the effects of the dopant heteroatom on the PL were revealed based on the combination of spectroscopic methods and theoretical calculations. The results indicated that the GQDs exhibit multiemissive centers for the PL emission mechanism. An excitation-independent PL emission band (band I) results from a high-energy transition originating from the quantum confinement of the carbon core (carbon π–π* transitions in sp2 domain), and an excitation-dependent PL emission band...

Synthesis of high fluorescence graphene quantum dots and their selective detection for Fe3+ in aqueous solution

In recent years, carbon particles have gained numerous attentions because of their simple synthetic process, low toxicity and water solubility. The present work involves synthesis of two types of graphene quantum dots (GQDs) by treating sulfydryl group (−SH) amino acid glutathione (GSH) in the presence and absence of AgNO3 via one pot route, respectively. The Ag+ ions from AgNO3 can combine the −SH from GSH to form Ag2S, thus surfaces of the obtained graphene quantum dots (N-GQDs) are mainly modified by some free hydroxyl groups (OH), amino groups (NH2) and carboxyl groups (COOH). In the absence of Ag+ ions, the surfaces of as-prepared graphene quantum dots (SN-GQDs) not only include OH, NH2 and COOH, but also −SH. Interestingly, as-prepared two kinds of GQDs both have strong fluorescence with different emission wavelength. More importantly, these GQDs have special recognition ability for metal ions. The N-GQDs respond rapidly towards the presence of Fe3+ ions, and can be used as a probe to detect Fe3+ ions in waste water, while the SN-GQDs have a special recognition to Hg2+ ions.

Graphene Quantum Dots for Theranostics and Bioimaging.

Since their advent in the early 1990s, nanomaterials hold promise to constitute improved technologies in the biomedical area. In particular, graphene quantum dots (GQDs) were conjectured to produce new or improve current methods used for bioimaging, drug delivery, and biomarker sensors for early detection of diseases. This review article critically compares and discusses current state-of-the-art use of GQDs in biology and health sciences. It shows the ability of GQDs to be easily functionalised for use as a targeted multimodal treatment and imaging platform. The in vitro and in vivo toxicity of GQDs are explored showing low toxicity for many types of GQDs.

Characteristics of graphene quantum dots determined by edge structures: three kinds of dots fabricated using thermal plasma jet

Model structures of the three types of graphene quantum dots; armchair (red), zigzag (blue), and hybrid (yellow) GQDs.

Balancing Light Absorptivity and Carrier Conductivity of Graphene Quantum Dots for High-Efficiency Bulk Heterojunction Solar Cells

Graphene quantum dots (GQDs) have been considered as a novel material because their electronic and optoelectronic properties can be tuned by controlling the size and the functional groups of GQDs. Here we report the synthesis of reduction-controlled GQDs and their application to bulk heterojunction (BHJ) solar cells with enhanced power conversion efficiency (PCE). Three different types of GQDs--graphene oxide quantum dots (GOQDs), 5 h reduced GQDs, and 10 h reduced GQDs--were tested in BHJ solar cells, and the results indicate that GQDs play an important role in increasing optical absorptivity and charge carrier extraction of the BHJ solar cells. The enhanced optical absorptivity by rich functional groups in GOQDs increases short-circuit current, while the improved conductivity of reduced GQDs leads to the increase of fill factors. Thus, the reduction level of GQDs needs to be intermediate to balance the absorptivity and conductivity. Indeed, the partially reduced GQDs yielded the outstandingly improved PCE of 7.60% in BHJ devices compared to a reference device without GQDs (6.70%).