The emerging graphene quantum dots (GQDs) and carbon dots (C-dots) have gained tremendous attention for their enormous potentials for biomedical applications, owing to their unique and tunable photoluminescence properties, exceptional physicochemical properties, high photostability, biocompatibility, and small size. This article aims to update the latest results in this rapidly evolving field and to provide critical insights to inspire more exciting developments. We comparatively review the properties and synthesis methods of these carbon nanodots and place emphasis on their biological (both fundamental and theranostic) applications.

Glowing Graphene Quantum Dots and Carbon Dots: Properties, Syntheses, and Biological Applications

Carbon Nanomaterials for Biological Imaging and Nanomedicinal Therapy

As new members of carbon material family, carbon and graphene quantum dots (CDs, GQDs) have attracted tremendous attentions for their potentials for biological, optoelectronic, and energy related applications. Among these applications, bio-imaging has been intensively studied, but optoelectronic and energy devices are rapidly rising. In this Feature Article, recent exciting progresses on CD- and GQD-based optoelectronic and energy devices, such as light emitting diodes (LEDs), solar cells (SCs), photodetctors (PDs), photocatalysis, batteries, and supercapacitors are highlighted. The recent understanding on their microstructure and optical properties are briefly introduced in the first part. Some important progresses on optoelectronic and energy devices are then addressed as the main part of this Feature Article. Finally, a brief outlook is given, pointing out that CDs and GQDs could play more important roles in communication- and energy-functional devices in the near future.

Carbon and Graphene Quantum Dots for Optoelectronic and Energy Devices: A Review

It is of great interest to develop new carbon-based materials as electrodes for supercapacitors because the conventional electrodes of activated carbons in supercapacitors cannot meet the ever-increasing demands for high energy and power densities for electronic devices. Due to their high electronic conductivity and improved hydrophilic properties, together with their easy syntheses and functionalization, N-doped carbons have shown a great potential in energy storage and conversion applications. In this review, after a brief introduction of electrochemical capacitors, we summarize the advances, in the recent six years, in the preparation methods of N-doped carbons for applications in supercapacitors. We also discuss and predict futuristic research trends towards the design and syntheses of N-doped carbons with unique properties for electrochemical energy storage.

Review on recent advances in nitrogen-doped carbons: preparations and applications in supercapacitors

Carbon dots: synthesis, formation mechanism, fluorescence origin and sensing applications

Nitrogen-doped carbon dots (CDs) have attracted great interest due to their extraordinary properties, especially their enhanced emission efficiency, and thus a facile synthesis of nitrogen-doped CDs with high emission efficiency is critical for practical applications. To improve the emission efficiency of CDs, herein we employed Bombyx mori silk, which has high nitrogen content, as a raw material to prepare photoluminescent nitrogen-doped carbon dots through one-pot hydrothermal synthesis, and found that the as-prepared CDs have a photoluminescence (PL) quantum yield of 13.9%, and display amphoteric properties depending on the pH, are highly photostable, have low toxicity and are suitable for bioimaging.

https://www.rsc.org/suppdata/tb/c3/c3tb20418a/c3tb20418a.pdf

One-pot hydrothermal synthesis of highly luminescent nitrogen-doped amphoteric carbon dots for bioimaging from Bombyx mori silk – natural proteins

https://www.rsc.org/suppdata/cc/c3/c3cc44624g/c3cc44624g.pdf

A surfactant-assisted redox hydrothermal route to prepare highly photoluminescent carbon quantum dots with aggregation-induced emission enhancement properties.

An environmental friendly method for the preparation of functionalized reduced graphene oxide (rGO) in aqueous solution is developed with great easiness, using heparin as both a reducing agent and an effective stabilizer. Structural and morphological studies have demonstrated that part of the oxygen functionalities in the graphene oxide can be removed by this method, and heparin can be functionalized on the resulting rGO sheets through hydrophobic and hydrogen bonding interactions. The functionalized rGO shows good stability in aqueous solution, owing to the strong electrostatic and steric repulsions of the heparin which adsorb on the surfaces of rGO sheets. Moreover, the rGO exhibits excellent biocompatibility and anticoagulant activity, making it a promising candidate for widespread use in the biomedical field.

Green and easy synthesis of biocompatible graphene for use as an anticoagulant

The self-assembly of two-dimensional (2D) graphene sheets into three-dimensional (3D) structures is an effective approach to fabricate graphene-based hierarchical architectures for practical applications. Here we report an easy and environmentally friendly method to fabricate a graphene-based multifunctional hydrogel using a biocompatible polysaccharide as both a stabilizer and a physical cross-linking agent. The as-prepared hydrogel is highly stable in a variety of harsh conditions such as strong acid, strong alkali, high ion strength solution, and organic solvent. Moreover, it shows excellent dye adsorption and antibacterial capability, and has been successfully used for miniature-scale water purification. The present work provides a new insight for the self-assembly of functionalized graphene with biomolecules, offering an alternative way to fabricate multifunctional materials for a wide range of applications.

Chun Fang Liu

Papers

One-pot hydrothermal synthesis of highly luminescent nitrogen-doped amphoteric carbon dots for bioimaging from Bombyx mori silk – natural proteins

A surfactant-assisted redox hydrothermal route to prepare highly photoluminescent carbon quantum dots with aggregation-induced emission enhancement properties.

Green and easy synthesis of biocompatible graphene for use as an anticoagulant

A facile and green method to fabricate graphene-based multifunctional hydrogels for miniature-scale water purification