Single-layer Graphene Quantum Dots Research Articles

Spray-lithography of hybrid graphene-perovskite paper-based photodetectors for sustainable electronics

Paper is an ideal substrate for the development of flexible and environmentally sustainable ubiquitous electronic systems. When combined with nanomaterial-based devices, it can be harnessed for various Internet-of-Things applications, ranging from wearable electronics to smart packaging. However, paper remains a challenging substrate for electronics due to its rough and porous nature. In addition, the absence of established fabrication methods is impeding its utilization in wearable applications. Unlike other paper-based electronics with added layers, in this study, we present a scalable spray-lithography on a commercial paper substrate. We present a non-vacuum spray-lithography of chemical vapor deposition (CVD) single-layer graphene (SLG), carbon nanotubes (CNTs) and perovskite quantum dots (QDs) on a paper substrate. This approach combines the advantages of two large-area techniques: CVD and spray-coating. The first technique allows for the growth of SLG, while the second enables the spray coating of a mask to pattern CVD SLG, electrodes (CNTs), and photoactive (QDs) layers. We harness the advantages of perovskite QDs in photodetection, leveraging their strong absorption coefficients. Integrating them with the graphene enhances the photoconductive gain mechanism, leading to high external responsivity. The presented device shows high external responsivity of ∼520 A W−1 at 405 nm at <1 V bias due to the photoconductive gain mechanism. The prepared paper-based photodetectors (PDs) achieve an external responsivity of 520 A W−1 under 405 nm illumination at <1 V operating voltage. To the best of our knowledge, our devices have the highest external responsivity among paper-based PDs. By fabricating arrays of PDs on a paper substrate in the air, this work highlights the potential of this scalable approach for enabling ubiquitous electronics on paper.

On electron propagation in triangular graphene quantum dots

Tight-binding models of electron propagation in single-layer triangular graphene quantum dots with armchair and zigzag edges are developed. The electron hoppings to the nearest and next-to-nearest neighbours on the honeycomb lattice as well as interactions with the confining Dirichlet and Neumann walls are incorporated into the resulting tight-binding Hamiltonians. Associated to the irreducible crystallographic root system A 2, the armchair and zigzag honeycomb Weyl orbit functions together with the related discrete Fourier–Weyl transforms provide explicit exact forms of the electron wave functions and energy spectra. The electronic probability densities corresponding to the armchair and zigzag dots are evaluated and their contrasting behaviour exemplified.

Multifunctional SGQDs-CORM@HA nanosheets for bacterial eradication through cascade-activated “nanoknife” effect and photodynamic/CO gas therapy

Infection associated with multidrug-resistant (MDR) bacteria has become a serious threat to public health, and there is an urgent demand of developing new antibiotics that offer combinatorial therapy to effectively combat MDR. Herein, a multifunctional two-dimensional nanoantibiotic was facilely designed and established on the basis of the covalent conjugation of CO-releasing molecule (CORM-401) and electrostatic adsorption of hyaluronic acid (HA) onto single-layered graphene quantum dots (SGQDs) to assemble SGQDs-CORM@HA nanosheets, abbreviated as SCH. Upon the enrichment of as-prepared nanoantibiotics in the community of targeted microbe, bacterial-secreted hyaluronidase (HAase) would cleave HA on SCH, and the sharp edges as well as the reactive sites on SGQDs-CORM nanosheets were exposed for cascade activation of synergistic antibacterial effects. Specifically, ultrathin SGQDs-CORM nanosheets can penetrate into bacterial cells deemed as the unique “nanoknife” effect. Under white light irradiation, SGQDs-CORM nanosheets can act as a high-efficient photosensitizer to generate cytotoxic singlet oxygen (1O2), as a well-recognized reactive oxygen species (ROS), to produce high oxidative stress and damage bacteria. As a complementary to photodynamic therapy (PDT), the accumulation of local ROS further triggered the release of CO to hinder the bacterial growth via causing plasma membrane damage and inducing metabolic disorders. Such synergistic treatment regimen arising from cascade-activated “nanoknife” effect and photodynamic/CO gas therapy, was devoted to outstanding on-demand antibacterial performance both in vitro and in vivo. Fascinatingly, the nanoplatform showed good biocompatibility toward both normal somatic cells and non-targeted bacteria. The remarkable antibacterial capability and admirable biocompatibility endow SCH with great potential to fight against MDR pathogens for in-coming clinical translations.

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.

Surface plasmon-induced photodegradation of methylene blue with single layer graphene quantum dots/Au nanospheres under visible-light irradiation

Single-layer graphene quantum dots and gold (SLGQDs/Au) nanospheres composite was synthesized by hydrothermal and photochemical methods. Single-layer graphene quantum dot was synthesized by glucose precursor via hydrothermal method and SLGQDs/Au nanocomposite was prepared by adding HAuCl4 under UV irradiation. Characterization of sample was performed using XRD, Raman, FESEM, UV–vis spectroscopy and PL analysis. The quantum yield of SLGQDs/Au composite was calculated. The role of surface plasmon resonance (SPR) of gold nanoparticles in quantum yield reduction and the effect of quantum yield on photodegradation was discussed. Using the optimal sample, a photocatalyst test was performed on methylene blue, which near 90% photocatalytic degradation was achieved under visible light irradiation in 120 min. Compared to bare GQD the high photocatalytic efficiency of composite could be due to the presence of SPR level of Au nanoparticles between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of SLGQDs. Under light irradiation, SLGQDs and Au nanoparticles absorb visible light energy. By absorbing the photons, the electrons of SLGQDS could be excited to LUMO band and leave holes in HOMO band. Spontaneously the emitted photons excite the Fermi level electrons of Au nanoparticles to the SPR state. Created SPR level can suppress electron-holes recombination. Then the photo-exited electrons react with dissolved oxygen to generate ° O2− and ° OH radicals meanwhile, the holes could oxide OH− into OH°. Created radicals which are strong oxidants degrade the pollutants.

Photoluminescence enhancement of single-layer graphene quantum dots by the surface plasmon resonance of Au nanocubes

Highly photoluminescent single-layer graphene quantum dots around Au nanocubes (SLGQDs/Au) were synthesized using a simple method. The SLGQDs were synthesized using a low-cost hydrothermal method from glucose as a precursor. The atomic force microscopy analysis proved that the average thickness of the GQDs is lower than 4 Å, meaning that the GQDs are single-layer dots. The novel cubic shape of the SLGQDs/Au nanocomposites was confirmed by field-emission scanning electron microscopy and Transmission electron microscopy. Structural characterization was performed by X-ray diffraction, energy-dispersive X-ray spectroscopy and Raman spectroscopy. Photoluminescence (PL) spectroscopy revealed that the obtained SLGQDs/Au nanocomposite has a higher PL emission peak intensity than that of the SLGQDs, which is due to the surface plasmon resonance of Au nanocubes at 530 nm, revealed in the UV–Vis absorption spectra. Finally, the effect of Au concentration on the PL emission peak intensity of the SLGQDs was studied, and the quantum yield of the optimum sample was measured and discussed.

Single-layer boron-doped graphene quantum dots for contrast-enhanced in vivo T1-weighted MRI.

Gadolinium (Gd)-based chelates are used as clinical T1 contrast agents for magnetic resonance imaging (MRI) due to their demonstrated high sensitivity and positive contrast enhancement capability. However, there has been an increasing safety concern about their use in medicine because of the toxicity of the metal ions released from these contrast agents when used in vivo. Although significant effort has been made in developing metal-free MRI contrast agents, none have matched the magnetic properties achieved by the gold standard clinical contrast agent, Gd diethylene penta-acetic acid (Gd-DTPA). Here, we report the development of a single-layer, boron-doped graphene quantum dot (termed SL-BGQD) that demonstrates better T1 contrast enhancement than Gd-DTPA. The SL-BGQD is shown to provide significantly higher positive contrast enhancement than the Gd-DTPA contrast agent in imaging vital organs, including kidneys, liver, and spleen, and especially, vasculatures. Further, our results show that the SL-BQGD is able to bypass the blood-brain barrier and allows sustained imaging for at least one hour with a single injection. Hematological and histopathological analyses show that the SL-BGQD demonstrates a non-toxic profile in wild-type mice and may, therefore, serve as an improved, safer alternative to currently available clinical MRI contrast agents.

Hybrid dye sensitized solar cell based on single layer graphene quantum dots

Single layer graphene quantum dots (SLGQDs, average size of ~ 9 nm) were added into N719/TiO2 nanoparticles photoanode (prepared using a doctor blade method) as co-sensitizer and photovoltaic properties were investigated for dye sensitized solar cell (DSSC) application. Low-cost and high-yield SLGQDs solution was synthesized with only glucose and DI water as precursor using a hydrothermal method. This method allows the tuning of optical properties and energy states by using appropriate precursors and synthesis conditions. Optical characterization reveals that the SLGQDs solution absorbs UV and visible light photons with wavelengths up to ~ 700 nm. For engineering a suitable energy state, and then to obtain an efficient DSSC, lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) of the SLGQDs were determined against vacuum energy level by utilizing a cyclic voltammetry measurement. Electrical measurements indicated an improvement in power conversion efficiency for the DSSC fabricated based on SLGQDs and N719 as co-sensitizers. The experimental analysis shows that this improvement arises from enhancement of charge collection and separation due to the cascaded alignment of the energy levels between N719/SLGQDs/TiO2 interfaces. By addition of SLGQDs into N719/TiO2 nanoparticles photoanode, we were able to increase the short circuit current density and efficiency by 39% (from 14.47 to 20.03 mA/cm2) and 35% (from 6.57% to 8.92%), respectively.

One-step preparation of single-layered graphene quantum dots for the detection of Fe3.

Single-layer graphene quantum dots are highly desirable while their facile and controllable preparations remain challenging. Herein, single-layered graphene quantum dots (sl-GQDs) were developed via a facile one-step hydrothermal synthesis, with citric acid and β-cyclodextrin (CD) as starting materials. The sl-GQDs decorated with CD molecules emit green fluorescence with a quantum yield of 5.34%, and exhibit a good response exclusively to ferric ions for their structural oxygenous groups. The linear range of the proposed sensor for ferric ions was found in a wide concentration range of 0-85 μM. The detection limit is about 0.26 μM. The sl-GQDs based sensing platform also demonstrates its feasibility in real water sample analysis with recoveries of 93.8%-101.5%.

One step synthesis of graphene quantum dots, graphene nanosheets and carbon nanospheres: investigation of photoluminescence properties

Single layer graphene quantum dots (GQDs), graphene nanosheets (GNSs), and carbon nanospheres (CNSs) were synthesized by an easy, environment-friendly, and low-cost hydrothermal process and the effect of the hydrothermal reaction time on their structural and photoluminescence properties was studied. Four different kinds of samples were prepared only using glucose and deionized water. By varying the hydrothermal reaction time, we obtained excitation-dependent photoluminescent GQDs and GNSs with different photoluminescence quantum yields (PLQYs) and CNSs without any photoluminescence. Atomic force microscopy images showed that the synthesized GQDs are single or double-layered. Transmission electron microscopy (TEM) images indicated that the sizes of the samples are distributed between the small graphene quantum dots (GQDs ≤ 10 nm) for reaction time of 2 h and the homogeneous carbon nanospheres (CNSs ∼ 560 nm) for reaction time of 30 h. Finally, it has shown that the optimized sample exhibits the high PLQY of 22.7% for reaction time of 8 h.

CO2 adsorption in nitrogen-doped single-layered graphene quantum dots: a spectroscopic investigation.

In this work, we investigate the adsorption process of CO2 in graphene quantum dots from the electronic structure and spectroscopic properties point of view. We discuss how a specific doping scheme could be employed to further enhance the adsorbing properties of the quantum dots. This is evaluated by considering the depth of the potential well, the spectroscopic constants, and the lifetime of the compound. Electronic structure calculations are carried out in the scope of the density functional theory (DFT), whereas discrete variable representation (DVR) and Dunham methodologies are employed to obtain spectroscopic constants and hence the lifetimes of the systems. Our results suggest that nitrogen-doped graphene quantum dots are promising structures as far as sensing applications of CO2 are concerned. Graphical Abstract Adsorption mechanism of the CO2 molecule in (a) a pristine and (b) a nitrogendoped Graphene Quantum Dot.

Dy(III)-induced aggregation emission quenching effect of single-layered graphene quantum dots for selective detection of phosphate in the artificial wetlands

Carbon quantum dots (CQDs), prepared by one-step hydrothermal treatment of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and triethylamine (TEA), could be exfoliated or delaminated into single-layered graphene quantum dots (s-GQDs) with methanol for the first time, with fluorescence (FL) emission at 500 nm when excited at 417 nm. The s-GQDs, with more sufficient carboxyl groups on the surface than CQDs, could be induced to be aggregated by metal ion dysprosium (Dy3+), resulting in aggregation-induced emission quenching effect subsequently. However, the presence of phosphate (PO43-) destroys the Dy3+-induced aggregates of s-GQDs owing to the strong coordination between Dy3+ and PO43-, inducing the FL emission recovery of the s-GQDs and providing selective detection method of PO43- in the artificial wetlands with the linear range of 0.2–30 μM and determination limit of 0.1 μM (3σ).

Dual-mode emission of single-layered graphene quantum dots in confined nanospace: Anti-counterfeiting and sensor applications

Engineering of the luminescent properties for graphene quantum dots (GQDs) presents two enormous challenges: 1) The bandgap of GQDs is mainly determined by structural defects (size, shape, and the fraction of sp2 and sp3 domains), which results in non-stoichiometric nature; 2) the preparation methods limit the achievement of an accurate chemical structure of GQDs, leading to many controversial explanations over the relationship between the structural defects and bandgaps. Here, single-layered GQDs with an exact structure are obtained by in-situ reaction of intercalated precursors in the confined nanospace of layered double hydroxides (LDHs). Subsequently, the structure-property relationship is uncovered, demonstrating the enhanced fluorescence and activated room temperature phosphorescence of the as-prepared GQDs-LDHs, which originate from synergistic effects: 1) strong confinement provided by the nanospace of LDHs; 2) rich O-containing functional groups on the surface of GQDs resulting from LDH catalysis. Moreover, the colorless nature and dual-emission characteristics of GQDs-LDHs satisfy the preconditions as anti-counterfeiting markers for protecting valuable documents (bank notes, commercial invoices, etc.). Particularly, owing to the low toxicity of GQDs and the edible property of LDHs, the GQDs-LDHs/gelatin capsules could be the new generation of potential green anti-counterfeiting material in the field of food and drugs.

Mitochondria-targeting single-layered graphene quantum dots with dual recognition sites for ATP imaging in living cells.

As a molecular unit of intracellular energy transfer, adenosine triphosphate (ATP) is significant for maintaining the energy balance in living cells and thus monitoring cellular ATP is important to assess cellular physiological functions. However, effective monitoring of cellular ATP still faces challenges owing to the similarity of ATP to other nucleoside polyphosphates. Herein, yellow emissive single-layered graphene quantum dots (s-GQDs) with dual recognition sites including π-conjugated single sheets and positively charged sites were developed. The s-GQDs exhibit a good mitochondria targeting ability and respond only to purine nucleotides and show good selectivity in discriminating tri-, di- and monophosphate nucleotides. The good selectivity should be attributed to the concurrent effect of π-π stacking and electrostatic interactions between filmy layered positive s-GQDs and negative purine nucleotides. Owing to the mitochondria targeting ability and dual recognition sites of the s-GQDs, the mitochondrial ATP fluctuation resulting from the activation and suppression of ATP in living cells has been successfully monitored.

Highly selective detection of phosphate ion based on a single-layered graphene quantum dots-Al3+ strategy

Determination of phosphate ion (PO43-) is important in biomedical and environmental arrays because its controlling concentrations are associated with different pathologies or the quality of water. Herein, we report a new type of photoluminescence (PL) probe for highly selective detection of PO43- based on a single-layered graphene quantum dots chelating with aluminium ions (s-GQDs-Al3+) system. The PL of s-GQDs can be enhanced by Al3+ through the aggregation-induced emission enhancement (AIEE) effect. With the addition of PO43-, the PL of the s-GQDs-Al3+ system is faded away because PO43- has stronger coordination with Al3+ which results in the elimination of AIEE effect and the decrease in the PL intensity of the s-GQDs-Al3+ system. Therefore, the s-GQDs-Al3+ system can behave as an on-off type PL probe for PO43- detection. It is found that the PL intensity ratio (I/I0) of s-GQDs in the presence of Al3+ at 463nm is proportional to the concentration of PO43- in the range of 0.25–7.5μM with the limit of detection as low as 0.1μM. This selective assay has a great application prospect in the complex matrixes owing to its simplicity and specificity for PO43- detection.

Synthesis of green-photoluminescent single layer graphene quantum dots: Determination of HOMO and LUMO energy states

Low-cost and high-yield green-photoluminescent single layer graphene quantum dots (SLGQDs) synthesized with only DI water and glucose as precursor using a hydrothermal method. Atomic force microscopy proved that the graphene quantum dots are single layers and transmission electron microscopy images showed that the average width of SLGQDs is about 8nm and optical characterization revealed that SLGQDs are highly photoluminescent. Highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the SLGQDs against vacuum determined using a cyclic voltammetry technique, and energy band gap was obtained ∼ 2.9 and 3.1eV from cyclic voltammetry and optical measurements, respectively.

Boron and nitrogen co-doped single-layered graphene quantum dots: a high-affinity platform for visualizing the dynamic invasion of HIV DNA into living cells through fluorescence resonance energy transfer.

High-affinity binding of carbon nanomaterials with nucleobases, which is still a challenge, is the basis for DNA directed assembly and sensing. In this work, boron and nitrogen co-doped single-layered graphene quantum dots (BN-SGQDs) are designed as a high-affinity platform for nucleic acid detection and imaging in living cells, which has been confirmed by density functional theory (DFT) simulation and experiments. Owing to their excellent absorption and photoluminescence ability, the high quantum yield (QY 36.5%) yellow fluorescent BN-SGQDs could act as an energy donor in the fluorescence resonance energy transfer (FRET) process for nucleic acid detection. Furthermore, this BN-SGQD based sensing platform has been successfully adopted to visualize the dynamic invasion of human immunodeficiency virus (HIV) DNA into HeLa cells. The high-affinity platform has shown potential for biosensing in complicated biological samples.

Self-exothermic reaction prompted synthesis of single-layered graphene quantum dots at room temperature.

The easy fabrication of single-layered graphene quantum dots (s-GQDs) still faces challenge. Herein, we report an efficient route to fabricate s-GQDs within 5 min at room temperature by introducing a simple self-exothermic reaction. The as-prepared s-GQDs can specifically bind with aluminium ions to produce an aggregation-induced emission enhancement effect.

Single-Layered and Single-Crystalline Graphene Quantum Dots from 2D Polycyclic Compounds

Single-Layered and Single-Crystalline Graphene Quantum Dots from 2D Polycyclic Compounds

C96H30 tailored single-layer and single-crystalline graphene quantum dots.

By controllable synthesis of a carbon precursor and with a suitable preparation routine, a series of single-layer and single-crystalline graphene quantum dots (GQDs) with uniform size distribution were prepared from C96H30. It was found that the absorption, photoluminescence (PL) and two-photon photoluminescence (TPPL) show a high size-dependent effect with a redshift that occurs as the size grows. Two-photon absorption (TPA) properties of GQDs were measured at 800 nm under a femtosecond pulse laser. Two-photon bioimaging of HeLa cells was carried out to determine TPA properties. Most significantly, the as-prepared GQDs showed potential in a practical application in two-photon cell bioimaging due to their high contrast TPPL. In addition, the superior nonlinear absorption, stable TPPL and excellent solubility were beneficial to the optical limiting (OL) properties.