Neuro-transmitters have been considered to be essential biochemical molecules, which monitor physiological and behavioral function in the peripheral and central nervous systems. Thus, it is of high pharmaceutical and biological significance to analyze neuro-transmitters in the biological samples. So far, researchers have devised a lot of techniques for assaying these samples. It has been found that electro-chemical sensors possess features of robustness, selectivity, and sensitivity as well as real-time measurement. Graphene quantum dots (GQDs) and carbon QDs (CQDs) are considered some of the most promising carbon-based nanomaterials at the forefront of this research area. This is due to their characteristics including lower toxicity, higher solubility in various solvents, great electronic features, strong chemical inertness, high specific surface areas, plenty of edge sites for functionalization, and versatility, in addition to their ability to be modified via absorbent surface chemicals and the addition of modifiers or nano-materials. Hence in the present review, the synthesis methods of GQDs and CQDs has been summarized and their characterization methods also been analyzed. The applications of carbon-based QDs (GQDs and CQDs) in biological and sensing areas, such as biological imaging, drug/gene delivery, antibacterial and antioxidant activity, photoluminescence sensors, electrochemiluminescence sensors and electrochemical sensors, have also been discussed. This study then covers sensing features of key neurotransmitters, including dopamine, tyrosine, epinephrine, norepinephrine, serotonin and acetylcholine. Hence, issues and challenges of the GQDs and CQDs were analyzed for their further development.

/pdf/carbon-and-graphene-quantum-dots-a-review-on-syntheses-2iwpnkv96w.pdf

Carbon and graphene quantum dots: a review on syntheses, characterization, biological and sensing applications for neurotransmitter determination

https://onlinelibrary.wiley.com/doi/pdf/10.1002/eem2.12038

Biomass-Derived Carbon Dots and Their Applications

Carbon and graphene quantum dots are prepared using top-down and bottom-up methods. Sustainable synthesis of quantum dots has several advantages such as the use of low-cost and non-toxic raw materials, simple operations, expeditious reactions, renewable resources and straightforward post-processing steps. These nanomaterials are promising for clinical and biomedical sciences, especially in bioimaging, diagnosis, bioanalytical assays and biosensors. Here we review green methods for the fabrication of quantum dots, and biomedical and biotechnological applications.

/pdf/green-synthesis-biomedical-and-biotechnological-applications-487df8fxdo.pdf

Green synthesis, biomedical and biotechnological applications of carbon and graphene quantum dots. A review

Abstract As an emerging material, nanomaterials have attracted extensive attention due to their small size, surface effect and quantum tunneling effect, as well as potential applications in traditional materials, medical devices, electronic devices, coatings and other industries. Herein, the influence of nanoparticle selection, production process, grain size, and grain boundary structures on the mechanical properties of nanomaterials is introduced. The current research progress and application range of nano-materials are presented. The unique properties of nano-materials make them superior over traditional materials. Therefore, nanomaterials will have a broader application prospect in the future. Research on nanomaterials is significant for the development and application of materials science.

https://www.degruyter.com/document/doi/10.1515/ntrev-2020-0021/pdf

Mechanical properties of nanomaterials: A review

Synthesis of graphene quantum dots from natural polymer starch for cell imaging

Abstract As a new class of fluorescent carbon materials, graphene quantum dots (GQDs) have attracted tremendous attention due to their outstanding properties and potential applications in biological, optoelectronic, and energy-related fields. Herein, top-down and bottom-up strategies for the fabrication of GQDs, mainly containing oxidative cleavage, the hydrothermal or solvothermal method, the ultrasonic-assisted or microwave-assisted process, electrochemical oxidation, controllable synthesis, and carbonization from small molecules or polymers, are discussed. Different methods are presented in order to study their characteristics and their influence on the final properties of the GQDs. The respective advantages and disadvantages of the methods are introduced. With regard to some important or novel methods, the mechanisms are proposed for reference. Moreover, recent exciting progresses on the applications of GQD, such as sensors, bio-imaging, drug carriers, and solar cells are highlighted. Finally, a brief outlook is given, pointing out the issues still to be settled for further development. We believe that new preparation methods and properties of GQDs will be found, and GQDs will play more important roles in novel devices and various applications.

/pdf/synthesis-and-applications-of-graphene-quantum-dots-a-review-2e1fdg4z8w.pdf

Synthesis and applications of graphene quantum dots: a review

Solar-driven production of hydrogen peroxide (H2 O2 ), as an important industrial chemical oxidant with an extensive range of applications, from oxygen reduction is a sustainable alternative to mainstream anthraquinone oxidation and direct hydrogenation of dioxygen methods. The efficiency of solar to hydrogen peroxide over semiconductor-based photocatalysts is still largely limited by the narrow light absorption to visible light. Here, the authors proposed and demonstrate the proof-of-concept application of light-generated hot electrons in a graphene/semiconductor (exemplified with widely used TiO2 ) dyad to largely extend visible light spectra up to 800 nm for efficient H2 O2 production. The well-designed graphene/semiconductor heterojunction has a rectifying interface with a zero barrier for the hot electron injection, largely boosting excited hot electrons with an average lifetime of ≈0.5 ps into charge carriers with a long fluorescent lifetime (4.0 ns) for subsequent H2 O2 production. The optimized dyadic photocatalyst can provide an H2 O2 yield of 0.67 mm g-1  h-1 under visible light irradiation (λ ≥ 400 nm), which is 20 times of the state-of-the-art noble-metal-free titanium oxide-based photocatalyst, and even achieves an H2 O2 yield of 0.14 mm g-1  h-1 upon photoexcitation by near-infrared-region light (≈800 nm).

Facilitating Hot Electron Injection from Graphene to Semiconductor by Rectifying Contact for Vis-NIR-Driven H2 O2 Production.

Graphene, a two-dimensional sheet of sp2-hybridized carbon atoms packed into a honeycomb lattice, can be combined with various polymers through different methods and techniques. Polymer/graphene nanocomposites are expected to not only preserve the fa-vorable properties of graphene and polymers, but also greatly enhance the intrinsic properties due to the synergetic effect between them. In this review, the preparation approaches of graphene/polymer nanocomposites, including melt blending, solution blending, in-situ polymeri-zation and in-situ synthesis, were presented comprehensively in order to study the relationship between these approaches and the final characteristics and performances. Each approach had different influences on the final properties of the nanocomposites. The advantages and disadvantages of the preparation methods were discussed respectively. Additionally, the application researches of the polymer/graphene nanocomposites as electrochemical sensors, were introduced in detail. With regard to some important or novel sensors, the mechanisms were proposed for reference. Finally, conclusions were given and the issues waiting to be settled for further development were pointed out. The current review demonstrates that polymer/graphene nanocomposites exhibit superior electrochemical performances and will be applied practically in the field of sensor devices.

Weimin Hu

Papers

Synthesis and applications of graphene quantum dots: a review

Synthesis of graphene quantum dots from natural polymer starch for cell imaging

Facilitating Hot Electron Injection from Graphene to Semiconductor by Rectifying Contact for Vis-NIR-Driven H2 O2 Production.

The Preparation Approaches of Polymer/graphene Nanocomposites and their Appilcation Research Progress as Electrochemical Sensors

Accelerating the activation of NO x - on Ru nanoparticles for ammonia production by tuning their electron deficiency