Endotoxin-Free Preparation of Graphene Oxide and Graphene-Based Materials for Biological Applications.

Due to their two-dimensional structure and unique properties, graphene and its derivatives have been extensively studied for their potential applications in various fields ranging from electronics to composites. Particularly, their high surface area, electrical conductivity, mechanical strength, dispersability in aqueous phase, and possibility of surface modification make them promising candidates for biomedical applications including biosensing, drug delivery, tissue engineering, cell imaging, and therapeutics. The functioning of graphene nanosheets in these applications is dependent on their structure and properties, which are mainly determined by their preparation and processing methods. Exfoliation techniques are the most common methods for preparation of graphene nanosheets for biomedical applications due to their high yield and scalability. Further modification of these methods is necessary to produce biocompatible and toxin-free graphene that can be safely incorporated into biological media. Here, we describe protocols for chemical and mechanical exfoliation of graphite to produce endotoxin-free and highly stable graphene oxide and graphene dispersions. Additional protocols are provided for proper pre- and post-processing of nanosheets and endotoxin measurement techniques.