The Dependence of the Graphene-Microbial Interactions on Graphene Dispersion Fishnet Effects
MetadataShow full item record
Graphene exhibits a unique chemical and physical structure that enables it to have numerous biomedical applications; however, various researchers have reached different and conflicting conclusions, and thus the safety and risk of graphene toxicity remains a serious concern. In order to begin analyzing the cytotoxic nature of graphene, an understanding of the properties of a graphene sheet in a dispersion is essential. The graphene concentration was measured, and the results from growing bacteria in graphene dispersions were analyzed according to the understanding of dispersion, in order to assess whether microbial growth was dependent on graphene dispersion behavior. The objective of this study is to analyze the dependence of graphene-microbial interactions on graphene dispersions by supporting the existence of an entraining effect , or fishnet effect, in graphene dispersions. The concentration is the main parameter manipulated in studying the forces involved in the fishnet concept, while entraining is simulated using graphite flakes poured on top of the dispersion. A reduction in concentration is observed when the centrifugation step is carried out three days after sonication versus sonication immediately after centrifugation. The entrainment simulation resulted in a 39% decrease in the concentration of a sample sonicated immediately after sonication and a 5% increase in a sample centrifuged three days after sonication, thus supporting the existence of a fishnet effect. The effects of graphene on microorganisms were studied by doing a plate agar test. The plate agar test resulted in uniform growth across the plate, but no observable toxicity or "kill zones”. The plate agar test was followed by growing bacteria in a liquid dispersion, in which an observable film formed at the top, but graphene sheets were observed to be present in the biofilm. It was also observed that the dispersion had destabilized over time, with sheets sedimenting to the bottom as the bio-film continued to grow. A crystal violet assay confirmed that there was a decrease in microbial growth in the presence of graphene, but a trend with changes in concentration was not observed. These observations, coupled with the data, support the dependence of graphene-microbial interactions on graphene dispersion effects independent of concentration. Also, as the sheets fall out of solution, microbial growth persists, indicating the conversion of few-layer sheets to multi-layer sheets mitigates graphene toxicity. Therefore, although graphene may reduce the rate or amount of microbial growth, with time, the destabilization of graphene sheets due to the fishnet effect may mitigate toxicity over time.