###### Abstract  
The antibacterial activity of graphene nanostructures (GrNs) on glass (G) and nickel (Ni) substrates against _Escherichia coli_ ATCC 35218 (Gram-negative) and _Staphylococcus aureus_ ATCC 25923 (Gram-positive) has been researched in this study. GrNs have been synthesized via two different methods, namely, chemical vapor deposition (CVD) and plasma enhanced chemical vapor deposition (PECVD). While the antibacterial effect of CVD-grown graphene nanosheets has been examined according to the number of layers (monolayer/1-2 layers/2-3 layers), the effect of PECVD grown Gr nanowalls on G substrates has been also analyzed at 100, 150, and 200 W radio frequency (RF) powers. For CVD-grown graphene nanosheets, as the number of layers of graphene nanosheets decreased, the cell viability (%) of _E. coli_ decreased from 100% to 51.4%. It has been shown that PECVD graphene nanowalls synthesized onto G substrates, especially at 200 W, exhibited stronger antibacterial activity against _E. coli_ and _S. aureus_, and the cell viabilities of _E. coli_ and _S. aureus_ decreased from 100% to 25.19% and 100% to 9.02%, respectively. It is concluded that that both the nanowall (3D structure) morphology, which changes significantly with the presence of RF power, and the defects created on the graphene surface using the PECVD method are more effective against _E. coli_ and _S. aureus_ than CVD-grown graphene-based samples (2D-structure). graphene; CVD; PECVD; _E. coli; S. aureus_; antibacterial activity +
Footnote †: journal: Applied Sciences  
have been increasing exponentially in the last decade. CBNs such as graphene (Gr) [11], graphene oxide (GO) [11; 12; 13], and reduced graphene oxide (rGO) [14] have been established to possess antibacterial activities and have attracted researchers for their antimicrobial properties. Fungi can easily colonize the surfaces of most devices and materials, and they can quickly spread fungal spores. Therefore, suitable material against fungi is extremely desired. The antifungal activities of graphene nanomaterials were studied by synthesizing different types of CBNs, such as Gr, GO, and rGO [2]. The applications of antibacterial and antifungal graphene-based nanomaterials are still relatively novel because a deeper comprehension of the underlying biological mechanisms is required [2]. Gr is a single-atom-thick sheet of hexagonally arrayed sp\({}^{2}\) hybridized carbon atom [15; 16]. Gr, obtained for the first time by [PERSON] et al. [16], has received great attention from researchers since then because of its electrical and optical properties, as well as its extraordinary physical properties, such as large surface-to-volume ratio, mechanical flexibility, and thermal stability [17; 18; 19; 20; 21; 22]. In literature, different methods are used for the synthesis of Gr, such as pulsed laser deposition (PLD), CVD, PECVD, and epitaxial procedures [19; 20; 21]. Looking at the practical applications of CVD and PECVD-GrNs, it is seen that GrNs can be synthesized on different substrates. Each procedure depends on many different parameters that play an important role in graphene quality [21; 22]. The Gr-based antibacterial tests have been generally applied mainly against _Escherichia coli_ (_E. coli_) and _Staphylococcus aureus_ (_S. aureus_). As seen in the literature, a lot of researchers have worked on the antibacterial activity of graphene-based materials, especially, Gr, rGO, and GO. Among them, [PERSON] et al. [23] showed the antibacterial activity of monolayer Gr films on Cu, Ge, and SiO\({}_{2}\). Especially, the growth of _E. coli_ and _S. aureus_ were inhibited by graphene films on Cu and Ge. [PERSON] et al. [24] examined the antibacterial activity of Gr nanosheets that could be applied in the development of biomedical devices. They observed that Gr nanosheets have antibacterial activities against _E. coli_. [PERSON] et al. [25] reviewed the antibacterial and antib Biofilm abilities of graphene and its derivatives in solution on the surface.