ABSTRACT
@#The abuse of antibiotics has been increasing bacterial resistance, which means there is a need to develop methods for the efficient detection and effective treatment of multiresistant bacterial infections. As one of graphene-based materials, graphene quantum dots (GQDs) have distinct mechanical, electrical, and optical properties, including a small size, a large surface area-to-volume ratio, biocompatibility, antimicrobial activity and tunable photoluminescence. Therefore, GQDs are expected to be widely used as antimicrobial materials, drug delivery carriers and photosensitizers in antibacterial applications. In this review, we focus on their synthesis, characteristics and antimicrobial applications in oral medicine.
ABSTRACT
We developed a rapid method to detect Cu2+and glutathione(GSH)based on the fluorescence quenching-recovery properties of graphene quantum dots(GQDs),which were synthesized by the gentle oxidation of graphite powder.The results revealed that the fluorescence intensity of GQDs versus concentration of Cu2+and GSH had good linearity, with the detection limits of 0.01 and 0.1 mmol/L, respectively.The fluorescence quenching was linearly proportional to the concentrations of Cu2+ranging from 1.0 to 10.0 mmol/L;the fluores-cence intensity was linearly enhanced with the concentrations of GSH ranging from 0.1 to 1.0 mmol/L.In addi-tion,the method was successfully applied to the determination of real samples with recoveries falling between 93％-101％ and 96％-107％,respectively.This method is simple,accurate and precise.There was no interference with other familiar co-existing metal ions and potential materials.
ABSTRACT
Functional groups may change the electrical characteristics of graphene quantum dots,thus leading to the improvement of their properties and related applications. To improve the optical properties,we designed and synthesized pentaethylene hexamine and dodecylamine functionalized graphene quantum dots (PEHA-GQD-DA). Citric acid was mixed with pentaethylene hexamine and heated at 170℃ for 0.5 h. Then dodecylamine was added and the reaction was continued at 160℃ for 1.5 h to obtain PEHA-GQD-DA. The Yesults revealed that the PEHA-GQD-DA was composed of the graphene sheets from 1 nm to 3 nm,and their edges contained abundant functional groups. The introduction of pentaethylene hexamine greatly improved the fluorescence emission. The fluorescence quantum yield reached 72.7%,which was much higher than that of the GQD prepared by the thermal hydrolysis of single citric acid. The introduction of dodecylamine created a special amphiphilic structure that allows the quantum dots more likely to enter cell through the phospholipid bilayer of cell membrane. The PEHA-GQD-DA exhibited an excellent optical behavior for pH value of the medium. Within pH range of 1.0-6.5, the fluorescence intensity increased with the increase of pH value. The fluorescence spectrum sensitively changed with the change of pH value. There was a good linear relationship between the maximum emission wavelength and the pH value. When the pH was in the range of 6.5-12.0,the fluorescence spectrum didn't change with the change of pH value. However, its fluorescence intensity linearly decreased with the increase of pH value. The existence of common inorganic ions and organic small molecules does not interfere with pH response of the quantum dots. The PEHA-GQD-DA has been successfully applied to fluorescent detection of pH value in water samples and Hela cell imaging.
ABSTRACT
A ball milling method which is green with simple-manipulation and low-cost was used to prepare graphene as precursor for graphene quantum dots (GQDs) synthesis.Subsequently, GQDs with good dispersibility, uniform size distribution, average diameter of (4.80 ± 0.20) nm and 1-3 layers were prepared by one-step hydrothermal method.The morphology, structure and optical properties of the GQDs were characterized by high-resolution transmission electron microscopy (HRTEM), atomic force microscope (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), UV-Vis absorption and fluorescence spectroscopy.Furthermore, the GQDs were used in label-free and specific detection of ferric ion (Fe.3+) with broad linear ranges of 2.0×10.-6-7.0×10.-4 mol/L and low detection limit of 1.8 × 10.6 mol/L (S/N=3).The possible mechanism was also discussed and the application of GQDs for Fe.3+ detection in tap water was demonstrated.Finally, based on their low cytotoxicity and excellent biocompatibility, the as-prepared GQDs were successfully applied to efficient cell imaging.This work provides a new way for preparation of carbon-based nanomaterials and build a foundation for deepening applications of GQDs in bio-/chem-analysis, bioimaging, etc.
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A label-free method for sensitive and selective detection of thrombin ( Tb) was constructed based on rare earth ion mediated fluorescence switch of graphene quantum dots ( GQDs) . Rare earth ion ( Er3+) can assemble onto the surface of GQDs through the coordination interaction between Er3+ ions and the carboxylate groups located on the surface or edge of the GQDs, resulting in the aggregation of the GQDs and thereby decrease of the fluorescence of the GQDs. In the presence of Tb, the oxygen and nitrogen-donor atoms in Tb can coordinate with Er3+ ions and compete with the carboxylate groups on GQDs to coordinate Er3+ ions, thus the interaction between GQDs and Er3+ ions is reduced, which lead to the restoration of the GQDs fluorescence. In this study, the sensing mechanism was demonstrated by transmission electron microscopy, atomic force microscope, Fourier transform infrared spectroscopy, UV-Vis absorption and fluorescence spectroscopy. The limit of detection for Tb assay was as low as 0. 049 nmol/L. Moreover, this assay was successfully applied to the selective determination of Tb in real samples.
ABSTRACT
A simple methodology was developed to quantify penicillamine (PA) in pharmaceutical samples, using the selective interaction of the drug with Cu-modified graphene quantum dots (Cu-GQDs). The proposed strategy combines the advantages of carbon dots (over other nanoparticles) with the high affinity of PA for the proposed Cu-GQDs, resulting in a significant and selective quenching effect. Under the optimum conditions for the interaction, a linear response (in the 0.10–7.50 μmol/L PA concentration range) was observed. The highly fluorescent GQDs used were synthesized using uric acid as single precursor and then characterized by high resolution transmission electron microscopy, Raman spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, fluorescence, and absorption spectroscopy. The proposed methodology could also be extended to other compounds, further expanding the applicability of GQDs.
ABSTRACT
A simple methodology was developed to quantify penicillamine (PA) in pharmaceutical samples, using the selective interaction of the drug with Cu-modified graphene quantum dots (Cu-GQDs). The proposed strategy combines the advantages of carbon dots (over other nanoparticles) with the high affinity of PA for the proposed Cu-GQDs, resulting in a significant and selective quenching effect. Under the optimum conditions for the interaction, a linear response (in the 0.10–7.50 μmol/L PA concentration range) was observed. The highly fluorescent GQDs used were synthesized using uric acid as single precursor and then characterized by high resolution transmission electron microscopy, Raman spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, fluorescence, and absorption spectroscopy. The proposed methodology could also be extended to other compounds, further expanding the applicability of GQDs.
ABSTRACT
<p><b>OBJECTIVE</b>To evaluate the bio-safety of graphene quantum dots (GQDs), we studied its effects on the embryonic development of zebrafish.</p><p><b>METHODS</b>In vivo, biodistribution and the developmental toxicity of GQDs were investigated in embryonic zebrafish at exposure concentrations ranging from 12.5-200 μg/mL for 4-96 h post-fertilization (hpf). The mortality, hatch rate, malformation, heart rate, GQDs uptake, spontaneous movement, and larval behavior were examined.</p><p><b>RESULTS</b>The fluorescence of GQDs was mainly localized in the intestines and heart. As the exposure concentration increased, the hatch and heart rate decreased, accompanied by an increase in mortality. Exposure to a high level of GQDs (200 μg/mL) resulted in various embryonic malformations including pericardial edema, vitelline cyst, bent spine, and bent tail. The spontaneous movement significantly decreased after exposure to GQDs at concentrations of 50, 100, and 200 μg/mL. The larval behavior testing (visible light test) showed that the total swimming distance and speed decreased dose-dependently. Embryos exposed to 12.5 μg/mL showed hyperactivity while exposure to higher concentrations (25, 50, 100, and 200 μg/mL) caused remarkable hypoactivity in the light-dark test.</p><p><b>CONCLUSION</b>Low concentrations of GQDs were relatively non-toxic. However, GQDs disrupt the progression of embryonic development at concentrations exceeding 50 μg/mL.</p>