An Investigation of Antimicrobial Properties of Grafoid Inc. Graphene Coatings

Abstract

Graphene materials have been the center of attention due to their physicochemical properties. Moreover, in the past decade, these materials have attracted increasing attention because of their antimicrobial properties. A variety of antimicrobial mechanisms, both physical and chemical have been proposed but they are not clearly elucidated or the evidence in the literature may be contradictory. Graphene materials in this project were provided by Grafoid Inc. as coatings on glass substrates. These materials were characterized by X-ray photoelectron spectroscopy and Raman spectroscopy to help understand the effects of different preparation methods and coating properties on their antimicrobial properties. Super oxide anion dependent and independent oxidative stress assays revealed that oxidative stress was not a major pathway to cell inactivation after one hour of contact. Three different microorganisms were placed in contact with the graphene coatings to study the effects of type and shape of microorganisms on cell death. Cells in close contact with the graphene surface were killed and coccal-shaped Staphylococcus epidermidis had the highest survival on the coatings regardless of the preparation method, surface coverage, and functionality of the coatings, whereas rod-shaped cells (Escherichia coli and Bacillus subtilis) had higher levels of death, with the Gram negative E. coli usually having a lower level of survival than the Gram positive B. subtilis. Among materials prepared by Method 1, fluorinated reduced graphene oxide coatings had the highest antimicrobial activity, whereas graphene oxide coatings had the lowest antimicrobial activity. Conversely, when (3-aminopropyl) triethoxysilane (APTES) was used in Method 2 to enhance the attachment of graphene coating to the glass surface, then the graphene oxide coatings had the highest and the fluorinated reduced graphene oxide coatings had the lowest antimicrobial activity. E. coli death increased slightly with increasing surface coverage of the coating, regardless of the preparation method and surface functionality of the coating. Contact time between bacterial cells and graphene coatings is also important as rod-shaped cells had almost 100% cell death after three hours of contact with graphene coatings prepared by Method 2.