Surface Of Graphene Quantum Dots Research Articles

Pioneering molecularly-level Fe sites immobilized on graphene quantum dots as a key activity descriptor in achieving highly efficient oxygen evolution reaction

The emergence of efficient electrocatalysts to facilitate the thermodynamically demanding and kinetically challenging oxygen evolution process (OER), which includes the coordinated transfer of four protons and four electrons, remains an issue. The effective transfer of energy encourages molecular-level control over key redox transitions involving small-molecule substrates (O2, and H2O), at or near electrode surfaces. While many molecular catalysts have been shown highly active for OER, immobilizing those onto the heterogenous solid matrices is challenging. Herein, graphene quantum dots (GQDs), a carbonaceous sub-class, was used as the solid matrices to conjugate the molecular catalyst onto its surface owing to its high surface area and electronic conductivity. Through the coordinated environment of the conjugated material, the molecular Fe sites on the GQDs surface exhibited outstanding OER features, achieving an ultra-low overpotential of 223 mV and 241 mV at a current density of 50 and 100 and mA/cm2, respectively, and excellent stability over 24 h. Our results marked a pioneering step in that through conjugation, these molecular sites were well dispersed at the GQDs matrices and were intrinsically active for OER.

Modulating fluorescent sensing of the pyrene-based ion pair receptor by docking on graphene quantum dots

We successfully synthesized squaramide-based ion pair receptor 3, possessing a cation binding domain linked to the receptor scaffold so as act as an electron-withdrawing group and enhance anion binding. This compound was able to efficiently and cooperatively bind anions in the presence of sodium cations. Using reference compounds 1 and 2, we demonstrated that the presence of a carbonyl group on the aromatic ring significantly enhances the efficiency of anion binding. The incorporation of this group in the structure of receptor 3, combined with other strongly electron-withdrawing groups located on another aryl subunit, enabled the receptor to bind salts even in the presence of water. Furthermore, the capacity for modular synthesis of diarylsquaramides allowed to obtain sensor 4, which features a pyrene moiety directly attached to the anion-binding domain, selectively sensing dihydrogen phosphate anions. Besides the signaling feature, the presence of pyrene rings facilitated the docking of sensor 4 onto the surface of graphene quantum dots, resulting in a conjugate with improved fluorescent properties.

Synthesis of graphene quantum dots inside a nanoreactor for fluorescence detection of dopamine

A label-free fluorescence sensor for selective detection of dopamine (DA) was developed by using graphene quantum dots (GQDs) as fluorescence probes. The GQDs were prepared via a top-down acid vapor oxidation strategy, in which a hollow carbon @ mesoporous silica nanosphere (h-C@mesoSiO2) serves as nanoreactor and only 1 mL of HNO3 was used as scissors for quickly cleaving the thin carbon layer in the nanospace of h-C@mesoSiO2. The method not only effectively avoids a tedious separation process but also endows GQDs with uniform size and good dispersion. And the as-prepared GQDs display good linear fluorescence response to DA in the range of 0.24–5.86 mM with a low detection limit of 12.7 nM. The proposed sensor shows high selectivity and satisfying recovery for DA detection in human urine. The good specificity toward DA may be due to a) the carboxyl groups on the surface of GQDs can interact with the amine functional groups in DA through electrostatic interactions and b) this specificity is further enhanced by the π–π interaction between GQDs and DA. Importantly, the work not only provides an avenue for the controllable synthesis of GQDs, but also expands the application of GQDs prepared by top-down method to DA sensor.

(Third Place Poster Award) Computational Assessment of the Optoelectronic Structure and Biomolecular Complexation of Graphene Quantum Dots

With novel materials getting smaller and their size falling to the nanometer scale, it becomes harder to fully characterize them by only using the experimental apparatus at hand. Therefore, taking advantage of computational methods proves to be trustworthy in filling those gaps and in aiding our experimental data to get a better understanding of the nanomaterials’ structural and electronic properties. Graphene quantum dots (GQDs) have recently become one of the flagships of carbon nanotechnology due to their remarkable physical properties and, when functionalized, an ability to become water soluble, biocompatible and capable of fluorescence in the visible and near-infrared. This makes them perspective carriers for therapeutic delivery and image-tracking. In order to assess the advantages of their utilization for a variety of bioapplications, we have investigated optical properties of doped GQDs and their interactions with biomolecules using a variety of molecular simulation approaches. True atomic ground state of the N-GQD is achieved via performing first-principle calculations based on density functional theory (DFT). DFT calculations also unrevealed the contributions of each functional group within the structure to HOMO–LUMO band edges. The adsorption of biomolecules and genes on the GQD surface has been further investigated with regards of the GQD structure, complementing experimental results that verify gene and drug complexation. Figure 1

Development of ternary nanocomposite based on ferrocenyl-modified graphene quantum dots for high-performance energy storage applications

Graphene quantum dots were synthesized in a simple one-step procedure using citric acid as starting material. 4-Ferrocenylbutanol as a battery-type electrode material was further used to modify the surface of graphene quantum dots based on hydrogen bonding and π-π interactions. Finally, the nanocomposites with different compositions were synthesized using different amounts of CNT and Fe3O4. Their electrochemical performance shows the properties of the final nanocomposite for practical application in supercapacitors. The final nanocomposite exhibits ideal battery-type capacity, including high capacity of 258 mAh g−1 at 2.5 A g−1, excellent cycle life (89.2 %), and high energy and power density of 75 Wh kg−1 and 6000 W kg−1 (in two electrode system), respectively. The results show superior electrochemical performance and improved ion transfer rate between the electrode/electrolyte surface. The superiority of the final nanocomposite indicates its special properties for potential applications in energy storage devices.

Investigating of the anticancer activity of salen/salophen metal complexes based on graphene quantum dots: Induction of apoptosis as part of biological activity

This research work is the first report on the synthesis and stabilization of [Fe-Salophen] and [Fe-Salen] complexes by two methods of surface modification and anchoring of synthesized Schiff base ligand on the surface of graphene quantum dots (GQDs). The GQDs contain oxygenated functional groups that can act as non-radiative electron-hole recombination centers. Therefore removing these oxygen functional groups may improve quantum yield by reducing or deactivating the surface. In this work, GQDs with the amine functional group were synthesized with a quantum yield of 37.48%. The physicochemical properties of GQDs were investigated by Ultraviolet–visible (UV–Vis) and fluorescence spectroscopies, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Powder X-ray diffraction (PXRD), Transmission electron microscope (TEM). The synthesis of GQDs-[Fe-Salen] and GQDs-[Fe-Salophen] was evaluated by FT-IR, Inductively coupled plasma atomic emission spectroscopy (ICP-AES) and Energy dispersive X-Ray analysis (EDX) analyses. Then, using MTT- assay, annexin V-FITC/PI, DAPI staining and cellular uptake assays, the biochemical activity of these complexes on the MCF7 cell line was investigated. The results shows that GQDs-[Fe-Salen] and GQDs-[Fe-Salophen] affect the survival of MCF7 cancer cells and, by nuclear fragmentation cause 35.77% and 19.41% of early apoptosis in cells, respectively. Also was found cellular uptake of GQDs-[Fe-Salen] is higher than that of GQDs-[Fe-Salophen].

Sugar moiety driven adsorption of nucleic acid on graphene quantum dots: Photophysical, thermodynamic and theoretical evidence

Integration of biologically important molecules with graphene quantum dots (GQDs) as a new class of luminescent water-soluble carbon materials, has drawn considerable attention for recent exciting progress on its biomedical applications. In order to avoid toxic semiconductor QDs, GQDs have shown great promise in detection of DNA and other biological applications and hence, fundamental understanding of processes of interactions is important and necessary. The present work establishes the significant role of sugar residue of nucleic acids in adsorption of graphene materials through experimental estimation of binding thermodynamics concomitant with density functional theoretical (DFT) simulation and a detailed evaluation of photophysical parameters. Maximum quenching efficiency of adenosine moiety coupled with the shift in the vibrations of the five-member ring of D-ribose demonstrates the adsorption of DNA on GQDs framework through sugar moieties. The observed experimental results are consistent with the favorable Gibb’s free energy calculated through theoretical simulation. DFT presenting orbital interactions and bonding mechanism of DNAs on GQDs confirms that adsorption on GQDs surface involves charge transfer from nucleobases to GQDs and adenosine, in particular, binds strongly through charge transfer of 0.032e from nitrogen atom to carbon of GQDs. The present investigation will provide insights in understanding the possible role of GQDs in cellular imaging, biosensing and as carriers in targeted drug delivery.

Molecular Dynamics Simulations of Docetaxel Adsorption on Graphene Quantum Dots Surface Modified by PEG-b-PLA Copolymers.

Cancer is associated with a high level of morbidity and mortality, and has a significant economic burden on health care systems around the world in almost all countries due to poor living and nutritional conditions. In recent years, with the development of nanomaterials, research into the drug delivery system has become a new field of cancer treatment. With increasing interest, much research has been obtained on carbon-based nanomaterials (CBNs); however, their use has been limited, due to their impact on human health and the environment. The scientific community has turned its research efforts towards developing new methods of producing CBN. In this work, by utilizing theoretical methods, including molecular dynamics simulation, graphene quantum dots (GQD) oxide was selected as a carbon-based nanocarriers, and the efficiency and loading of the anticancer drug docetaxel (DTX) onto GQD oxide surfaces in the presence and in the absence of a PEG-b-PLA copolymer, as a surface modifier, were investigated. According to the results and analyzes performed (total energy, potential energy, and RMSD), it can be seen that the two systems have good stability. In addition, it was determined that the presence of the copolymer at the interface of GQD oxide delays the adsorption of the drug at first; but then, in time, both the DTX adsorption and solubility are increased.

Preparation and evaluation of a double-hydrophilic interaction stationary phase based on bovine serum albumin and graphene quantum dots modified silica

The bovine serum albumin (BSA) was firstly bonded on the surface of graphene quantum dots (GQDs) functionalized silica as the stationary phase named as BSA@GQDs@SiO2 which can perform hydrophilic interaction between the stationary phase and analytes. Characteristic methods including Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA), thermogravimetric analysis (TGA) and scanning electron microscope (SEM) were applied to estimate the chemical bonding results and morphological features of the prepared materials. In the chromatographic evaluation part, the BSA@GQDs@SiO2 column showed excellent separation efficiency for the analysis of hydrophilic compounds involving nucleosides and bases, acids, phenols, quinolones, vitamins and alkaloids, which proved the prepared column can exhibit hydrophilic interaction mode with other interactions including hydrogen bonding and electrostatic interaction. What's more, essential experimental approaches were designed to evaluate the retention properties of the prepared column via comparing with a commercial amino column and a prepared GQDs@SiO2 column. Results indicated the prepared column showed excellent separation ability for different kinds of hydrophilic compounds than commercial and single hydrophilic columns. The study showed that BSA@GQDs@SiO2 stationary phase with double hydrophilic materials will be a potential chromatographic material for analyzing various hydrophilic analytes.

Hydrophobic@amphiphilic hybrid nanostructure of iron-oxide and graphene quantum dot surfactant as a theranostic platform

Nanostructure hybrids offer exceptional properties and multifunctionality, suitable for the field of theranostics. Graphene quantum dots (GQDs) and magnetic nanoparticles (MNPs) are two possible candidates to be used these hybrids due to their chemical, physical and biological properties. GQDs can be modified to act as surfactants. In this study, a hybrid nanostructure of GQDs and MNP has been synthesized based on hydrophobic interactions between long carbon chains on the surface of GQDs on the surroundings and MNP at the center. We have synthesized GQDs through a pyrolysis process and modified them with cetyl alcohol to obtain a surfactant-GQDs (CAGQDs). Moreover, Iron-oxide nanoparticles (IONP) as MNP has been synthesized using oleate-iron complex. Afterward, CAGQDs and IONP are hybridized, leading to a structure in which IONP is located at the center, and it is surrounded by CAGQDs (IONP@CAGQD). IONP@CAGQD possesses fluorescent and magnetic properties. Moreover, hydrophobic and hydrophilic cargo loading abilities, contrast enhancement, targeting abilities, and stimuli-responsiveness are other features of this structure. Furthermore, Low cytotoxicity of IONP@CAGQD makes its biomedical applications possible. IONP@CAGQD can potentially be used as a multifunctional theranostic agent.

Synthesis of surface dual-template molecularly imprinted silica nanoparticles for extraction of ciprofloxacin and norfloxacin

Synthesis of selective dual-template molecularly imprinted silica nanoparticles (MI-SiNPs) on the surface of graphene quantum dots (GQDs) for the simultaneous extraction of ciprofloxacin (CIP) and norfloxacin (NOR) from biological samples.

What Happens When a Complementary DNA Meets miR-29a Cancer Biomarker in Complex with a Graphene Quantum Dot.

MicroRNAs (miRNAs), short single-stranded noncoding RNA molecules, serve as potential cancer biomarkers due to their involvement in cancer development. One of the strategies to extract miRNAs is to perform the miRNA adsorption on nanomaterials and dissociation by a complementary DNA strand (DNA probe). Recently, graphene quantum dots (GQDs) were found to show a good ability to absorb miRNAs. Thus, in this work, the mechanism of the GQD-adhered miRNA capture by its complementary DNA is revealed using molecular dynamics simulations. miR-29a, a potential cancer biomarker, is used as a miRNA model. Three systems containing one and four chains of miR-29a in addition to one and four complementary DNA probes (1R1D, 1R4D, and 4R4D) were studied. GQDs are the prime targets of a DNA attack. The full coverage of GQDs is required to protect the adsorption of DNA probes on the GQD face. The nucleobase-backbone interactions are the main contributors to miR-DNA interactions in this work. The interbase paring becomes small because most nucleobases of miR-29a and their probe are stacked to maintain their secondary structures, and some are absorbed on the GQD surface. Apparently, weakening of the nucleobase-GQD π-π stacking and the intrabase-pairing strength is needed for extracting miR-29a by a probe. Although no GQD-absorbed miR-29a desorption is found here, the basic principles obtained can be useful for further utilization of GQDs and their derivatives for miRNA extraction and detection.

Single-layered graphene quantum dots with self-passivated layer from xylan for visual detection of trace chromium(Vl)

Single-layered graphene quantum dots (GQDs) are commonly prepared through bottom-up strategy by aromatic molecules or other carbon precursors with complicated procedure. Herein, single-layered GQDs were firstly fabricated by nonaromatic xylan only with the assistance of NaOH/urea under hydrothermal conditions. Due to the gases (ammonia and carbon oxide) released by decomposition of urea, GQDs were single-layered and hindered from interaction and aggregation for the protection of self-passivated layer. The synthesized GQDs showed a fluorescent quantum yield of 23.8%, self-passivated xylan layer on the surface of GQDs avoided ions-induced interference, and were only destroyed by strong oxidants like those containing Cr(VI). And there were the inner filter effect and static quenching for chelating interaction between Cr(VI) and nitrogen, oxygen functional group from GODs. These results entrusted GQDs with good selectivity and sensitivity toward Cr(VI). Furthermore, in order to realize on-site visual detection of Cr(VI), a microfluidic chip and a smartphone were used to construct portable detection platform. The linear detection range was from 3 μM to 75 μM and the limit of detection was 0.10 μM, which was lower than that of GQDs solution through fluorescence spectrophotometer. Therefore, this equipment provides a simple method to on-site monitor water environment.

Modeling the Adsorption of the miR-29a Cancer Biomarker on a Graphene Quantum Dot.

MicroRNAs (miRNAs) are small noncoding RNA molecules associated with the regulation of gene expression in organisms. MiRNAs are focused on as potential cancer biomarkers due to their involvement in cancer development. New potential techniques for miRNA detection are rapidly developed, while there is a lack of effective extraction approaches, especially for miRNAs. Recently, graphene quantum dots (GQDs) have been involved in many disease biosensor platforms including miRNA detection, but no application in miRNA extraction is studied. To extract miRNAs, miRNA adsorption and desorption on GQDs are the key. Thus, in this work, the adsorption mechanism of miRNA on GQDs in solution is revealed using molecular dynamics simulations. The aim is to explore the possibility of using GQDs for miRNA extraction. The folded miR-29a molecule, one of the key cancer biomarkers, is used as a miRNA model. Two systems with one (1miR) and four (4miR) chains of miR-29a were set. MiR-29a molecules in all systems are simultaneously adsorbed on the GQD surface. Our finding highlights the ability of the GQD in collecting miRNAs in solution. In 1miR, the whole miR-29a chain sits on the GQD face, whereas all miR-29a molecules in 4miR show the “clamping” conformation. No “lying flat” orientation of miR-29a is observed due to the existence of the preserved hairpin region. Interestingly, the 5′ end shows tighter binding than the 3′ terminus. A design of complementary DNA with the recognition segment involving the sequences close to the 3′ end can promote effective miR-29a desorption.

Hyaluronic acid-graphene quantum dot nanocomposite: Potential target drug delivery and cancer cell imaging.

Nowadays, the use of nanoparticle-based drug delivery systems has received much more attention. In this regard, here, graphene quantum dots (GQD) were used as drug carriers as well as imaging agents for cancer cells. In order to optimize the dose of the drug and reduce its side effects for healthy cells, hyaluronic acid was decorated on the surface of GQD to target cancer cells. The morphology and size of the synthesized nanoparticles alone and conjugated with hyaluronic acid were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM); TEM images revealed a particles size of ∼5.67 and ∼8.69 nm, respectively. In the presence of 1-ethyl-3-[3(dimethylamino)propyl]carbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS), hyaluronic acid was bounded to dopamine hydrochloride and was prepared to react with GQD. After synthesis of graphene quantum dot-hyaluronic acid nanocomposite, curcumin (CUR) as a drug model was loaded on the synthesized nanocarriers, and its loading percentage was measured. The results showed that 98.02% of the drug was loaded on the nanocarriers. Also, the conjugation of each agent on the nanocarrier was approved by photoluminescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), and UV-visible absorption techniques, and the results showed that the reactions were performed correctly. The effect of GQD, graphene quantum dot-hyaluronic acid, CUR, graphene quantum dot-hyaluronic acid-CUR on the viability of HeLa and L929 cells was evaluated by the MTT test. The results showed that the synthesized nanocarrier is completely biocompatible, and the drug nanocarriers reduce HeLa cell viability significantly due to the mediation of hyaluronic acid-CD44 for drug cell uptake. Simultaneously with drug delivery, the other goal of these nanocarriers is to image cancer cells by emitting fluorescent light. Fluorescent microscopy showed that these nanocarriers were adsorbed on HeLa cells, unlike L929 cells.

Eco-Friendly 1,3-Dipolar Cycloaddition Reactions on Graphene Quantum Dots in Natural Deep Eutectic Solvent.

Due to their outstanding physicochemical properties, the next generation of the graphene family—graphene quantum dots (GQDs)—are at the cutting edge of nanotechnology development. GQDs generally possess many hydrophilic functionalities which allow their dispersibility in water but, on the other hand, could interfere with reactions that are mainly performed in organic solvents, as for cycloaddition reactions. We investigated the 1,3-dipolar cycloaddition (1,3-DCA) reactions of the C-ethoxycarbonyl N-methyl nitrone 1a and the newly synthesized C-diethoxyphosphorylpropilidene N-benzyl nitrone 1b with the surface of GQDs, affording the isoxazolidine cycloadducts isox-GQDs 2a and isox-GQDs 2b. Reactions were performed in mild and eco-friendly conditions, through the use of a natural deep eutectic solvent (NADES), free of chloride or any metal ions in its composition, and formed by the zwitterionic trimethylglycine as the -bond acceptor, and glycolic acid as the hydrogen-bond donor. The results reported in this study have for the first time proved the possibility of performing cycloaddition reactions directly to the p-cloud of the GQDs surface. The use of DES for the cycloaddition reactions on GQDs, other than to improve the solubility of reactants, has been shown to bring additional advantages because of the great affinity of these green solvents with aromatic systems.

Preparation and evaluation of a poly(N-isopropylacrylamide) derived graphene quantum dots based hydrophilic interaction and reversed-phase mixed-mode stationary phase for complex sample analysis

The poly(N-isopropylacrylamide) (NIPAAm) was first polymerized onto the surface of graphene quantum dots (GQDs) functionalized silica as packing materials via reversible addition-fragmentation chain transfer (RAFT) polymerization reaction, which can expand the interaction modes between stationary phase and analytes. A series of characteristic methods were selected to estimate the chemical bonding results of silica, involving Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). The prepared column can exhibit reversed-phase and hydrophilic interaction modes, which were demonstrated by the retention of eight kinds of target analytes with different Log P values. The column was then applied to separate banlangen granules and further verified by HPLC tandem time-of-flight mass spectrometry (HPLC/QTOF-MS). In conclusion, Sil-GQDs-PNIPAAm stationary phase improved the analysis range and performance of traditional phases, exhibiting flexible selectivity and application prospect for both hydrophobic and hydrophilic analytes.

Highly sensitive label-free fluorescence determination of lymphotropic virus DNA based on exonuclease assisted target recycling amplification and in-situ generation of fluorescent copper nanoclusters

Specific and sensitive detection of target DNA plays a significant role in clinical diagnosis and biomedical research. Herein, a sensitive ratio fluorescence biosensor was constructed based on in-situ generation of fluorescent copper nanoclusters (CuNCs) on the DNA modified graphene quantum dots (GQDs) for the detection of HTLV-I DNA. Firstly, large amount of AT rich single DNA (o-DNA) can be released from the designed hairpin DNA in the presence of trace target DNA via exonuclease III assisted target recycling amplification strategy. Then, the released o-DNA hybridized with the complementary DNA1 which was modified on the surface of GQDs, and the formed hybridized DNA with blunt 3′-hydroxylated terminus that couldn’t be digested by exonuclease I could act as the template for the generation of fluorescent CuNCs. While in the absence of target DNA, the o-DNA couldn’t be released, thus the DNA1 with 3′overhang ends could be degraded by exonuclease I, which resulted in the in-situ generation of fluorescent CuNCs on the surface of GQDs was blocked owing to the lack of DNA template. The GQD fluorescence in the GQD-CuNC nanohybrid was almost uninfluenced during the whole process. Therefore, with the GQD serving as the reference and CuNC acting as the reporter signal, there was an excellent linear relationship between the change of fluorescence intensity ratio (F595/F445) and the concentration of HTLV-I DNA in the range of 20 pM-12 nM with a detection limit of 10 pM. Furthermore, the biosensor exhibited satisfactory results for monitoring the presence of HTLV-I DNA in human serum.

A Fluorescence Resonance Energy Transfer Biosensor Based on Graphene Quantum Dots and Protoporphyrin IX for the Detection of Melamine.

Graphene quantum dots (GQDs), which have high photostability, anti-photobleaching and scintillation, good biocompatibility and low toxicity, are important member of the fluorescent material family, and have attracted extensive research interest. In this paper, a fluorescence resonance energy transfer (FRET) biosensor based on protoporphyrin IX (PpIX) and GQDs was developed for melamine detection. PpIX was bound to the surface of GQDs to produce self-assembled nanosensors, and a FRET process occurred between GQDs and PpIX. However, due to the combination of melamine and PpIX, the FRET process was shut down in the presence of melamine. The FRET system could quickly and accurately detect melamine with a detection range of 1.0 × 10-8 to 2.0 × 10-6mol/L based on the fluorescence intensity ratio of PpIX and GQDs, and the detection limit was 3.6 × 10-9mol/L. This method obtained satisfactory results when it was employed to the determination of melamine in milk samples.

Graphene Quantum Dots' Surface Chemistry Modulates the Sensitivity of Glioblastoma Cells to Chemotherapeutics.

Recent evidence has shown that graphene quantum dots (GQDs) are capable of crossing the blood–brain barrier, the barrier that reduces cancer therapy efficacy. Here, we tested three alternative GQDs’ surface chemistries on two neural lineages (glioblastoma cells and mouse cortical neurons). We showed that surface chemistry modulates GQDs’ biocompatibility. When used in combination with the chemotherapeutic drug doxorubicin, GDQs exerted a synergistic effect on tumor cells, but not on neurons. This appears to be mediated by the modification of membrane permeability induced by the surface of GQDs. Our findings highlight that GQDs can be adopted as a suitable delivery and therapeutic strategy for the treatment of glioblastoma, by both directly destabilizing the cell membrane and indirectly increasing the efficacy of chemotherapeutic drugs.