Brief Introduction to Graphene Physics & Chemistry
Graphene is a single- or few-layered sheet of Sp2-bonded carbon atoms. It can be produced by either top-down (e.g., the mechanical scotch tape method and chemical exfoliation from graphite) or bottom-up (e.g., chemical vapor deposition) methods. The unique physical and chemical properties of this 2D nanomaterial have interested scientists from various fields. The most intriguing property of graphene is its remarkably high electron mobility and its size-dependent electrical properties, making it a promising material in high-performance electronic devices. Optically, graphene shows light absorption from UV to near-infrared (NIR) regions. It has also been found that graphene oxide (GO) exhibits a size-dependent visible and NIR fluorescence, although the mechanism is not yet fully understood.[3,24,25] Graphene contains largely dislocated π-electrons that allow energy transfer from the nearby molecules, leading to efficient fluorescence quenching, useful in optical-based detection of biomolecules.[13,17,20,26–31]
The chemistry of graphene has also been widely investigated in the past few years. Intensive efforts have been devoted to fabricate large-area monolayered graphene with minimal defects via various possible chemical routes for applications in electronic devices and transparent conductors;[22,32] whereas for biomedical applications of graphene in physiological environments, proper surface functionalization on graphene is demanded to render high water solubility and biocompatibility. Both covalent and noncovalent strategies have been explored for graphene functionalization.[21,24] Hummers oxidization to generate GO is probably the oldest and most commonly used graphene chemistry. Further conjugation of hydrophilic polymers could further improve the stability of GO in salts and biological solutions.[2,3] Other covalent chemistry, such as 1,3-dipolar cycloaddition, a functionalization strategy widely used for carbon nanotubes, has also been developed to modify graphene. For the non-covalent chemistry, various molecules and polymers can be used to functionalize graphene via hydrophobic bindings or ϖ-ϖ interactions. The latter case is particularly interesting for drug delivery as many aromatic drug molecules can be physically adsorbed on the polyaromatic graphene surface by ϖ-ϖ stacking, which usually takes place in the aqueous phase for less water-soluble drugs.[2,3,5–7]
Nanomedicine. 2011;6(2):317-324. © 2011 Future Medicine Ltd.
Cite this: Graphene in Biomedicine: Opportunities and Challenges - Medscape - Mar 01, 2011.