Sulfur-doped Graphene Quantum Dots Research Articles

Covalent Attachment of Sulfur-doped Graphene Quantum Dots to Glucose Oxidase via Diimide-activated Amidation

The conjugation of biomolecules to quantum dots has recently gained attention in the field of bionanotechnology. Graphene quantum dots (GQDs) have been employed in various sensing applications due to their tunable fluorescence, controllable size, low cytotoxicity, and high biocompatibility. In this work, sulfur-doped graphene quantum dots (S-GQDs) were conjugated to glucose oxidase (GOx) for the potential detection of glucose. Fluorescent S-GQDs were synthesized via one-step pyrolysis of citric acid and thioglycolic acid at 200 °C. S-GQDs were conjugated to GOx using the carbodiimide/succinimide (EDC/NHS) coupling reaction, followed by purification via centrifugal ultrafiltration. Fluorescence spectroscopy, UV-Vis absorption spectroscopy, and transmission electron microscopy were employed to characterize the S-GQDs and S-GQD-GOx conjugates. The S-GQDs obtained had an average diameter of 49.8 ± 7.4 nm (n = 12) and emitted strong blue fluorescence (λem = 460 nm) when excited with 365-nm UV light. Trinder’s assay was used to assess the catalytic activity of free GOx and the S-GQD-GOx conjugates. The S-GQD-GOx conjugates consistently showed significantly greater catalytic activity compared to free GOx. The results obtained open avenues for the fabrication of a sensitive fluorescent GQD-based glucose probe in the future.

Adsorption and gas-sensing investigation of oil dissolved gases onto nitrogen and sulfur doped graphene quantum dots

Burning hydrocarbons as fuel, which produces carbon dioxide and water, is a major contributor to anthropogenic global warming. Hydrocarbons are introduced into the environment through their extensive use as fuels and chemicals as well as through leaks or accidental spills during exploration, production, refining, or transport of fossil fuels. Herein, theoretical calculations based on density functional theory (DFT) was applied to investigate the adsorption behavior of C2H4, CH4 and H2 on graphene quantum dot surfaces doped with Nitrogen (N) and sulfur (S) (GQD_N, GQD_S). Theoretical calculations in this study were obtained with the dispersion correction in consideration so as to predict intermolecular interactions alongside B3LYP-D3(BJ)/6-311+G (d, p). The sites that were doped with N and S atom were found to be more stable and suitable for gas adsorption. The adsorption energy was computed to establish the surface abilities of the adsorptions under investigation. Gas adsorptions on surfaces showed similar high negative values. We may deduce from the computed adsorption energies that GQD_N and GQD_S have strong adsorptions and considered adsorptions are thermodynamically favored. The ellipticity parameter calculated using the quantum theory of atoms in molecules (QTAIM), as well as the stabilization energies obtained from natural bond orbitals (NBO), confirmed the stability of surfaces upon gas adsorptions. QTAIM also confirmed remarkable intermolecular interactions. This result also agrees with that for non-covalent interactions, which predicted weak intermolecular interactions between surface and gas molecules. GQD_N and GQD_S are good adsorbents that can adsorb C2H4, CH4, and H2 gases, respectively.

Nitrogen- and sulfur-doped graphene quantum dots for chemiluminescence.

Graphene quantum dots (GQDs), as one of the most promising luminescent nanomaterials, have been receiving increasing attention in various applications. However, it is still a challenge to improve their chemiluminescence (CL) quantum efficiency. Herein, the CL emissions of nitrogen- and sulfur-doped GQDs (NS-GQDs), nitrogen-doped GQDs (N-GQDs) and undoped GQDs synthesized through one-pot high-temperature pyrolysis are investigated in their chemical reactions with bis(2-carbopentyloxy-3,5,6-trichlorophenyl) oxalate (CPPO) and hydrogen peroxide (H2O2). A bright blue emission, and yellowish green and yellowish white light from NS-GQDs, N-GQDs and GQDs can be observed, respectively, in the mixture solutions with CPPO and H2O2. For the first time, spooling CL spectroscopy was used to investigate the CL reaction mechanisms, illuminant decays and the absolute CL efficiencies of these three GQD systems. Compared with the same system of undoped GQDs, it has been found that the NS-GQDs not only present slower illuminant decay, but also display an absolute CL quantum efficiency of 0.01%, 5-fold enhancement, due to the increase in N and S doping for a well-defined band gap energy. Moreover, three peak wavelengths attributed to intrinsic emission at 425 nm, aggregation-induced emission (AIE) at 575 nm and S-doped emissive surface states at 820 nm are observed for the first time in the NS-GQD system. The CL spectrum of N-GQDs displays two emission peaks at 395 and 575 nm attributed to intrinsic emission and AIE, whereas the CL spectrum of undoped GQDs demonstrates 500 nm and 600 nm peak wavelengths attributed to core emission and AIE. Absolute CL quantum efficiencies from these emissions at these various peaks can be determined quantitatively. This study provides guidance on tuning the surface states of GQD for more conducive injection of electrons and holes, facilitating the production of CL emission, which is beneficial for promoting the development of optical, bioassay and energy conversion applications.

Enhanced visible-light photocatalytic activity of ZnS/S-graphene quantum dots reinforced with Ag2S nanoparticles

Today, contamination of water resources by pesticides and their presence in the food chain is one of the environmental problems. An economical method to eliminate of pesticides is the degradation in the presence of sunlight, which intensifies the need to design and manufacture new generation photocatalysts with short gap bands to accelerate the process of optical degradation. In this study, sulfur-doped graphene quantum dots (SG QDs) were successfully synthesized by the hydrothermal method and stabilized on the surface of ZnS semiconductor nanoparticles. Then, the core–shell structure of ZnS-SG QDs was decorated and reinforced with Ag2S nanoparticles. After confirming the structure of the prepared photocatalyst by X-ray diffraction (XRD), fourier transform infrared (FT-IR), scanning, and transmission electron microscopy (SEM & TEM) analyses, the photocatalyst's ability to optically degrade the two organophosphorus toxins diazinon and fenitrothion was evaluated. The results showed that the presence of Ag2S improved the photocatalytic activity and increased the degradation efficiencies to amount 40% for diazinon and fenitrothion. Furthermore, kinetic study showed that the photocatalytic degradation is initially followed by first order model and after that the mechanism is possibly changed to the second order model.

Pt nanoclusters based on N, S co-doped graphene quantum dots as a smart probe for ultrasensitive Ag+ sensing

In this work, a simple strategy for the rapid detection of Ag+ based on nitrogen, sulfur doped graphene quantum dots (N, S-GQDs) decorated platinum nanoclusters (PtNCs) was proposed for the first time. N, S-GQDs decorated PtNCs (N, S-GQDs@PtNCs) were prepared by a reduction method using ascorbic acid (AA) as reducing agent and N, S-GQDs as a stabilizer and morphology directing reagent, respectively. The N, S-GQDs@PtNCs have an excellent peroxidase activity, which could catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 to lead to an obvious color change. However, Ag+ could be reduced to Ag0 by N,S-GQDs, and the Ag0 covered the surface of N, S-GQDs@PtNCs causing its peroxidase activity to decrease. Ag+ concentration could be quantified by measuring the maximum absorption signal at 652 nm for oxidized TMB with a wide linear range of 0.5–300.0 nM and a limit of detection (LOD) as low as 0.2 nM. In addition, satisfactory results were obtained for the detection of Ag+ in actual water samples. The prepared colorimetric sensor had advantages such as simple operation, cost-effective, fast response, and visualization, and had great potential in detecting toxic Ag+ in environmental.

Field-amplified sample injection and graphene quantum dot dual preconcentration in the analysis of melamine and dicyandiamide by capillary electrophoresis

通过热解法制备了硫掺杂的石墨烯量子点(S-GQDs),同石墨烯量子点(GQDs)相比,S原子的引入有效改善了GQDs的表面状态和化学特性、增强其对正电荷的捕获能力,使其更易与阳离子相互作用。以S-GQDs为载体,结合电堆积富集技术,发展了一种基于场放大进样(FASI)和S-GQDs放大的双重富集毛细管电泳(CE)分离检测三聚氰胺和双氰胺的方法。三聚氰胺和双氰胺在酸性介质中带正电荷,电动进样时快速迁移到毛细管入口端进行FASI预富集;同时带负电荷的S-GQDs向阳极端迁移,在样品与缓冲溶液的界面处通过静电作用吸附样品离子,S-GQDs作为载体使检测信号进一步放大。实验考察了缓冲溶液中S-GQDs的体积分数、缓冲溶液的组成及pH、进样时间等因素对富集分离效果的影响。当缓冲溶液的pH为4.6时,进样时间可延长至450 s。同常规电动进样(10 kV×10 s)相比,采用FASI与S-GQDs双重放大技术可使检测灵敏度提高1.6×105倍。该方法对三聚氰胺和双氰胺检测的线性范围是1.0×10-14~1.0×10-8mol/L,相关系数(r2)大于0.999,检出限分别为2.6×10-15和5.7×10-15mol/L。实现了对盐酸二甲双胍中三聚氰胺和双氰胺的高灵敏检测,回收率分别为95.9%~102.4%和92.0%~106.0%,相对标准偏差(RSD)小于5%。该方法操作简单,分离效果好,准确度高,重现性好,适用于分离检测不同盐酸二甲双胍制剂中的三聚氰胺和双氰胺。

New bidental sulfur-doped graphene quantum dots modified with gold as a catalyst for hydrogen generation

Disadvantages of fossil fuels encourage researchers to develop clean combustion sources, in particular, H2 due to the high potential energy and safe by-products. Herein, Au was deposited on S-doped graphene quantum dots to obtain a heterogeneous photocatalyst for the degradation of formic acid toward H2 generation. Insertion of thiol groups on graphene quantum dots was carried out by self-condensation reaction of citric acid in the presence of Dimaval, as the thiol groups carrier. After the complexation of Au with the prepared S-doped graphene quantum dots, the catalytic activity of composite was evaluated in formic acid degradation to generate H2 under visible light. Au@S-doped graphene quantum dots demonstrated superior catalytic activity with the turnover frequency up to 112 h−1. The reaction enjoys significant benefits such as stability and recyclability of the catalyst, excellent reaction rate, and mild reaction conditions.

Trifunctional Graphene Quantum Dot@LDH Integrated Nanoprobes for Visualization Therapy of Gastric Cancer (Adv. Healthcare Mater. 16/2021)

Nanoprobes In article number 2100512 by Yechang Qian, Shilong Wang, and co-workers, trifunctional LDH@SGQD-VP16 integrated nanoprobes are composed of layered double hydroxides (LDHs), sulfur-doped graphene quantum dots (SGQDs) with stable fluorescence, and etoposide (VP16). Which can simultaneously achieve targeted aggregation, fluorescence visualization, and chemotherapy. This work provides a theoretical and experimental basis for LDH@SGQD-VP16 as a potential multifunctional agent for visualization therapy of gastric cancer.

Trifunctional Graphene Quantum Dot@LDH Integrated Nanoprobes for Visualization Therapy of Gastric Cancer.

Visualization technology has become a trend in tumor therapy in recent years. The superior optical properties of graphene quantum dots (GQDs) make them suitable candidates for tumor diagnosis, but their tumor targeting and drug-carrying capacities are still not ideal for treatment. Sulfur-doped graphene quantum dots (SGQDs) with stable fluorescence are prepared in a previous study. A reliable strategy by associating layered double hydroxides (LDHs) and etoposide (VP16) is designed for precise visualization therapy. Trifunctional LDH@SGQD-VP16 integrated nanoprobes can simultaneously achieve targeted aggregation, fluorescence visualization, and chemotherapy. LDH@SGQD-VP16 can accumulate in the tumor microenvironment, owing to pH-sensitive properties and long-term photostability in vivo, which can provide a basis for cancer targeting, real-time imaging, and effect tracking. The enhanced therapeutic and attenuated side effects of VP16 are demonstrated, and the apoptosis caused by LDH@SGQD-VP16 is ≈2.7 times higher than that of VP16 alone, in HGC-27 cells. This work provides a theoretical and experimental basis for LDH@SGQD-VP16 as a potential multifunctional agent for visualization therapy of gastric cancer.

Effect of sulfur-doped graphene quantum dots incorporation on morphological, optical and electron transport properties of CH3NH3PbBr3 perovskite thin films

Effect of sulfur-doped graphene quantum dots incorporation on morphological, optical and electron transport properties of CH3NH3PbBr3 perovskite thin films

Application of sulfur-doped graphene quantum dots@gold-carbon nanosphere for electrical pulse-induced impedimetric detection of glioma cells

Glioma is the predominant brain tumor with high death rate. The successful development of biosensor to achieve an efficient detection of glioma cells at low concentration remains a great challenge for the personalized glioma therapy. Herein, an ultrasensitive pulse induced electrochemically impedimetric biosensor for glioma cells detection has been successfully fabricated. The 4–11 nm sulfur-doped graphene quantum dots (S-GQDs) are homogeneously deposited onto gold nanoparticles decorated carbon nanospheres (Au–CNS) by Au-thiol linkage to form S-GQDs@Au–CNS nanocomposite which acts as dual functional probe for enhancing the electrochemical activity as well as conjugating the angiopep-2 (Ang-2) for glioma cell detection. Moreover, the application of an externally electrical pulse at +0.6 V expend the surface of glioma cells to accelerate the attachment of glioma cells onto the Ang-2-conjugated S-GQDs@Au–CNS nanocomposite, resulting in the enhanced sensitivity toward glioma cell detection. An ultrasensitive impedimetric detection of glioma cells with a wide linear range of 100–100,000 cells mL−1 and a limit of detection of 40 cells mL−1 is observed. Moreover, the superior selectivity with long-term stability of the developed biosensor in human serum matrix corroborates the feasibility of using S-GQDs@Au–CNS based nanomaterials as the promising sensing probe for practical application to facilitate the ultrasensitive and highly selective detection of cancer cells.

Confined Mesospace Synthesis of Sulfur-Doped Graphene Quantum Dots for the Direct Detection of H <sub>2</sub>O <sub>2</sub> Without the Aid of the Third Party

Confined Mesospace Synthesis of Sulfur-Doped Graphene Quantum Dots for the Direct Detection of H <sub>2</sub>O <sub>2</sub> Without the Aid of the Third Party

Targeted bioimaging and sensing of folate receptor-positive cancer cells using folic acid-conjugated sulfur-doped graphene quantum dots.

Forthe first time is reporteda facile in situ synthesis of folic acid-conjugated sulfur-doped graphene quantum dots (FA-SGQDs) through simple pyrolysis of citric acid (CA), 3-mercaptopropionic acid (MPA), and FA. The as-prepared FA-SGQDs were extensively characterized to confirm the synthesis and incidence of FA molecule on the surface of SGQDs through advanced characterization techniques. Upon excitation at 370-nm wavelength, FA-SGQDs exhibited blue fluorescence with an emission band at 455nm. While exhibiting relatively high quantum yield (~ 78%), favorable biocompatibility, excellent photostability, and desirable optical properties, the FA-SGQDs showed suitability as a fluorescent nanoprobe to distinguish the folate receptor (FR)-positive and FR-negative cancer cells. The experimental studies revealed that FA-SGQDs aptly entered into FR-positive cancer cells via anon-immunogenic FR-mediated endocytosis process. Additionally, the FA-SGQDs exhibited excellent free radical scavenging activity. Hence, these FA-SGQDs hold highpromise to serve as efficient fluorescent nanoprobes for the pre-diagnosis of cancer through targeted bioimaging and other pertinent biological studies. Graphical abstract.

One-step synthesis of sulfur-incorporated graphene quantum dots using pulsed laser ablation for enhancing optical properties.

To tune the electronic and optoelectronic properties of graphene quantum dots (GQDs), heteroatom doping (e.g., nitrogen (N), boron (B), and sulfur (S)) is an effective method. However, it is difficult to incorporate S into the carbon framework of GQDs because the atomic size of S is much larger than that of C atoms, compared to N and B. In this study, we report a simple and one-step method for the synthesis of sulfur-doped GQDs (S-GQDs) via the pulsed laser ablation in liquid (PLAL) process. The as-prepared S-GQDs exhibited enhanced fluorescence quantum yields (0.8% → 3.89%) with a huge improved absorption band in ultraviolet (UV) region (200 ∼ 400 nm) and excellent photo stability under the UV radiation at 360 nm. In addition, XPS results revealed that the PLAL process can effectively facilitate the incorporation of S into the carbon framework compared to those produced by the chemical exfoliation method (e.g., hydrothermal method). And also, the mechanisms related with the optical properties of S-GQDs was investigated by time-resolved photoluminescence (TRPL) spectroscopy. We believe that the PLAL process proposed in this study will serve as a simple and one-step route for designing S-GQDs and opens up to opportunities for their potential applications.

Correction to "Sulfur-Doped Graphene Quantum Dots as a Novel Fluorescent Probe for Highly Selective and Sensitive Detection of Fe3+".

Correction to "Sulfur-Doped Graphene Quantum Dots as a Novel Fluorescent Probe for Highly Selective and Sensitive Detection of Fe3+".

Sulfur doped graphene quantum dots as a potential sensitive fluorescent probe for the detection of quercetin

In this work, a novel, selective and sensitive fluorescent probe (sulfur doped graphene quantum dots, SGQDs) was designed for real-time detection of quercetin in red wine samples. SGQDs were synthesized by pyrolyzing citric acid (CA) and 3-Mercaptopropionic acid (MPA) and characterized through advanced techniques. It was observed that fluorescence intensity of SGQDs could be substantially quenched by the addition of quercetin through inner filter effect (IFE) mechanism. Additionally, a visual color change (colorless to light yellow) was also noticed after addition of quercetin into a solution of SGQDs. The change in SGQDs fluorescence intensity with varying quercetin content revealed good linearity in the 0–50.0 μM range with regression coefficient of 0.9943 and a lowest detection limit of 0.006 μg/mL. To authenticate the real-time application of SGQDs as a potential fluorescent probe, red wine samples having different quercetin concentrations were used for quantitative analysis, after the optimization of several analytical parameters.

A highly sensitive and selective detection of picric acid using fluorescent sulfur-doped graphene quantum dots.

The development of an analytical probe to monitor highly mutagenic picric acid (PA) carries enormous significance for the environment and for health. A novel, simple and rapid fluorescence analytical assay using sulfur-doped graphene quantum dots (SGQDs) was designed for the highly sensitive and selective detection of PA. SGQDs were synthesized via simple pyrolysis of 3-mercaptopropionic acid and citric acid and characterized using advanced analytical techniques. Fluorescence intensity (FI) of SGQDs was markedly quenched by addition of PA, attributed to the inner filter effect and dominating static quenching mechanism between the two, in addition to a significant colour change. The calibration curve of the proposed assay exhibited a favourable linearity between quenched FI and PA concentration over the 0.1-100 μΜ range with a lowest detection limit of 0.093 μΜ and a correlation coefficient of 0.9967. The analytical assay was investigated for detection of trace amounts of PA in pond and rain water samples and showed great potential for practical applications with both acceptable recovery (98.0-100.8%) and relative standard deviation (1.24-4.67%). Analytical performance of the assay in terms of its detection limit, linearity range, and recovery exhibited reasonable superiority over previously reported methods, thereby holding enormous promise as a simple, sensitive, and selective method for detection of PA.

Synthesis, characterization and investigation of synergistic antibacterial activity and cell viability of silver-sulfur doped graphene quantum dot (Ag@S-GQDs) nanocomposites.

The excessive use of traditional antibiotic and antibacterial agents has globally increased the growth of antibiotic-resistant bacteria that poses serious health risks. Therefore, the development of new generation antibacterial or antimicrobial agents for effective inhibition of bacterial growth is highly desired. In this study, we report a facile one-step synthesis approach for the preparation of a nanocomposite composed of silver nanoparticles (AgNPs) decorated with sulfur-doped graphene quantum dots (S-GQDs). The nanocomposite was comprehensively characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis absorption spectra, Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The characterization results demonstrated that the AgNPs were closely and uniformly surrounded by the S-GQDs, and consequently, this ensured the dispersion and stability of the so formed nanocomposite (Ag@S-GQDs). Further, the antibacterial activity of the Ag@S-GQDs nanocomposite was investigated and compared with bare S-GQDs and AgNPs against Gram-positive S. aureus (MTCC 737) and Gram-negative P. aeruginosa (MTCC 424) bacteria using macrodilution and agar well diffusion methods. Minimum inhibitory concentration (MIC) values of 70 and 35 μg mL-1 of the Ag@S-GQDs nanocomposite were found to be sufficient to hinder the growth of P. aeruginosa and S. aureus. A fractional inhibition concentration (FIC) index below 0.5 confirmed the existence of a synergistic effect between AgNPs and S-GQDs in the Ag@S-GQDs nanocomposite. In addition, the cytotoxicity of the Ag@S-GQDs nanocomposite, AgNPs and S-GQDs was also investigated using HEK 293 cell lines. Interestingly, the Ag@S-GQDs nanocomposite exhibited superior cell viability as compared to AgNPs and S-GQDs. These improved antibacterial and biocompatibility data demonstrate that the Ag@S-GQDs nanocomposite can serve as a promising antibacterial agent for industry to fabricate next-generation self-sterile textiles, antibacterial coatings and useful health care products supporting cell viability.

Nitrogen–Sulfur-Doped Graphene Quantum Dots with Metal Ion-Resistance for Bioimaging

The development of ultrastable and highly fluorescent heteroatoms-doped graphene quantum dots (GQDs) for bioimaging remains a challenge due to the fluorescence quenching caused by binding between t...

Facile Synthesis of Sulfur Doped Graphene Quantum Dots for High Performance Supercapacitor Applications

A comprehensive study of an efficient pseudocapacitor electrode material has been done for sulfur doped graphene quantum dots (S-GQDs). Two different electrode materials were prepared by selecting two different sulfur containing powders that is, MgSO4.7H2O (sample-I), CuSO4.7H2O (sample-II), as source material by using the facile hydrothermal method. HRTEM results show that sample-II (∼5–20 nm) had a small size in comparison to sample-I (∼10–50 nm). The measured specific capacitance for sample-II was found to be 133 Fg−1 at 0.1 mAg−1 is much higher than in sample-II due to enhancement in electrical conductivity and improvement in the electron transfer between electrodes and electrolyte.