Chapter 2 - Synthetic routes to graphene preparation from the perspectives of possible biological applications

Abstract

Preparation of graphene by specific routes and their relevance to biological applications has been compared here. After necessary discussion on numerous methods of graphene preparation, the major thrust of this chapter was devoted to the preparation of high-quality graphene for biological and biomedical applications. The bottom-up synthesis of graphene using chemical vapor deposition (CVD) or chemical synthesis is discussed first, followed by elaborate descriptions of liquid-phase exfoliation methods. The focus is then further narrowed down to biologically relevant, aqueous-phase exfoliation by ultrasonication, shear/turbulence, ball milling, and electrochemical routes. The production cost of graphene by these methods generally is as low as $3–$5 per gram in water, highly economical compared to commercially available graphene ($80–$100 per gram) or graphene oxide ($100–$120 per gram). The resulting graphene layers were almost defect free with ID/IG as low as 0.1–0.3 (ratio increases with defects), whereas the CVD method generally shows that of 0–0.1 (defect free). Furthermore, we discussed new opportunities to make bio-grade, sterile graphene suspensions in cell media or sera or common biological buffers which are relevant to the biological community. These are water dispersible, stable, nearly defect-free graphene rather than commonly used alternatives such as graphene oxide or reduced graphene oxide, which are known to have numerous defect sites.