Electrochemical Responses of Graphene with Biofilm Formation on Various Metallic Substrates By Using Laboratory Biofilm Reactors

Abstract

We have confirmed that graphene is very sensitive to biofilm formation by environmental biota and by some special bacteria (E.coli and S.epidermidis). Therefore, graphene is not recommended for biomaterials used in the human body. Graphene’s high sensitivity could lead to infections. On the other hand, this high sensitivity might allow grapheme to serve as a sensor for detecting biofilm formation at a very early stage. To obtain more data, we investigated the change of electrochemical responses for graphene on various substrates (while biofilms were forming on these samples). Biofilms were formed on metallic substrates. The procedure is briefly described. A mechanical exfoliation method was repeated by using scotch tape. For each final stage, the graphene on the scotch tape was transferred to the surface of a metallic sheet-type specimen. (Various specimens were used.) The graphene formed on the metallic specimens was confirmed by using Raman spectroscopy and by staining. For the staining, 0.1% crystal violet was used. We expected that the extent of graphene formation would increase with the repeated number of attachments between tapes. Therefore, some transferred specimens, with different repeated numbers than others, were prepared as specimens. Then they were immersed in culture liquids (LB culture liquids and HI ones) including E.coli and Staphylococcus epidermidis. The specimens were also immersed into rotational-type reservoirs filled with culture liquids including bacteria. Each specimen was fixed with a special jig and the culture liquids were stirred continuously. Two laboratory biofilm reactors (a static type and a flow type reactor) were used for this work. Measurements of electrochemical responses (Cyclic voltammetry, immersion potential etc.) were made for all samples, while the changes of Raman shifts with time on those specimens were observed too. Also the final states of the specimens were checked by using crystal violet. Finally, behaviors were analyzed and the applicability to sensing biofilm formation was discussed.