Functionalization of graphene sheets and their antibacterial activity

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Alsouqi, Deema Ghaleb
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An-Najah National University
Graphene is a thin flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice. It is one of the most studied materials nowadays because it has a high surface area and unique properties. However, graphene is considered a hydrophobic material (has a low solubility and dispersability in physiological solution), which leads to aggregation and precipitation in cell tissue and causing toxicity for different types of cells. For this purpose, functionalization of graphene has its purpose to improve its dispersability in water and its biocompatibility for various biomedical applications. The aim of this work is to covalently functionalize the graphene sheets with various charged groups (positive, negative and neutral) to improve its water dispersability, study its antibacterial activity and to determine the effect of charge on the activity. The graphene sheets had successfully functionalized covalently with three different groups (COOH, amine and tetraethylene glycol). The functionalization was confirmed by infrared spectroscopy and transmission electron microscope images. The functionalization demonstrates good dispersability in water and the degree of functionalization was quantified using the thermogravimetric analysis obtaining 32% of the functionalization in the case of graphene-TEG, 33% of graphene-amine and 47% of graphene-COOH. The antibacterial activity was determined primarily by agar diffusion disk- and well-variant method. Agar diffusion well-variant demonstrated the presence of the antibacterial activity for all graphene derivatives. In additional step, the antibacterial activity was detected and quantified through determining the MIC of the graphene derivatives by broth microdilution method. MIC was 250µg/ml for graphene-amine and graphene-TEG and 125µg/ml in the case of graphene-COOH. Moreover, the reduction of bacterial concentration after exposure to graphene derivatives was detected by the plate count method, the result shows that the bacterial reduction was increased in functionalized graphene nanomaterials with the complete growth inhibition in the case of graphene-COOH on both bacteria (E. coli and S. aureus). Graphene toxicity mechanism was investigated by in vitro graphene-mediated oxidation of glutathione, the loss of glutathione activity was the maximum for graphene-COOH with a reduction of 83%. Finally, graphene-COOH and graphene-TEG showed good hemo-compatibility, which supports their further in vivo studies.