Graphene, carbon nanotubes (CNT), and fluorescent carbon quantum dots (CQDs) pertain to carbon materials family. They have attracted much attention in the scientific community and engineering due to their extraordinary physical, chemical, optical, mechanical, thermal properties. Graphene is the thinnest two-dimensional material comprised of a one-atom-thick planar sheet of sp2-bonded carbon atoms, while carbon nanotubes have a cylindrical nanostructure which also consisted of sp2-bonded carbon atoms. Graphene can be perceived as the basic structure of graphite, carbon nanotubes, and fullerene. Carbon nanotubes are tube-shaped carbon material and can be divided into two types: single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).
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Figure 1. The schematics of the representative carbon-based nanomaterials .
Carbon nanoparticles have extraordinary electrical conductivity, heat conductivity, and mechanical properties. They are composed of pure carbon, therefore, exhibiting high stability, good conductivity, low toxicity, environmental friendliness. Since a large part of the human body consists of carbon, it is generally thought as a biocompatible material. The good electrical conductivity, high surface area, and linear geometry make their surface highly accessible to the electrolyte. Carbon-based nanomaterials also have strong anisotropic thermal conductivity. This property allows the carbon-based nanomaterials being used in advanced computing electronics where the temperature of uncooled chips can reach over 100℃.
1. Drug and gene delivery
The exploration of carbon-based nanomaterials in biomedical applications is at the early stages, but has attracted tremendous attention. One hot topic is its application in drug and gene delivery. For example, some research studies have shown that CNT can be bonded with a single strand of DNA can be bonded, and can then be successfully inserted into a cell. By functionalizing and chemically modifying of the sidewall, CNT can also be used as vascular stents and neuron growth and regeneration. The application as drug delivery is very common in carbon-based nanoparticles, especially the graphene-based nanoparticles. The π-conjugated structure of six-atom rings of can be conceptually considered as a planar aromatic macromolecule. This unique structure offers a large loading capability to a variety of fluorescent probes and drugs. The chemical modification of graphene can allow the conjugation with targeting ligands, therefore, achieve the targeted delivery of the drug. Both in vitro and in vivo studies have provided the evidence of the graphene for delivering anti-cancer drugs to the desired location of tumor cells, rather than the normal and healthy cells.
Carbon-based materials have been long investigated in many imaging applications. For example, fluorescence imaging (FL), two-photon FL, Raman imaging, magnetic resonance imaging (MRI), tomography (CT), photoacoustic imaging (PAI), computed positron emission tomography/single photon emission computed tomography (PET/SPECT), and multimodal imaging . Recently, a new form of carbon-based nanomaterials, carbon quantum dots, has attracted tremendous interests in its bioimaging applications. Since the original report in 2006, CQDs has been widely investigated for is fluorescent property. Similar to traditional QDs, CQDs possess size-dependent tunable emission and can resistant to photobleaching, making it desired for as bioimaging agent. Moreover, it also overcomes the severe toxicity of traditional QDs composed of heavy metals such as cadmium. Therefore, its bioimaging and biological labeling applications has been extensively examined in both cells and animal models.
3. Energy storage
Due to the dwindling of fossil fuel resources, the implementation of practical alternative energy systems becomes extremely important. Fuel cells may be one of the most likely energy sources. Carbon-based nanomaterials have been widely investigated as the catalysts and key components of hydrogen storage systems. Due to their intrinsic characteristics, carbon-based materials are a desired material as electrodes in capacitors and batteries. CNTs have shown a high reversible capacity for use in lithium-ion batteries and also in a variety of fuel cell components. The high electrical conductivity also allows the CNT be used in current collectors and gas diffusion layers. The high surface area and thermal conductivity make CNT and graphene very useful as electrode catalyst supports in fuel cells.
- Yan, Qi-Long, et al. "Highly energetic compositions based on functionalized carbon nanomaterials." Nanoscale 8.9 (2016): 4799-4851.
- Lin, Jing, Xiaoyuan Chen, and Peng Huang. "Graphene-based nanomaterials for bioimaging." Advanced drug delivery reviews (2016).