## 1 Introduction
Surface topographies with microscale and nanoscale features have been shown to play an important role in a number of cellular responses; for example, in relation to cell adhesion, it is demonstrated that bacteria respond to nanostructured surfaces by modulating their attachment behavior [52; 53; 54]. Recent studies suggest that surface nanofeature parameters (e.g., height, diameter and spacing) correlate with the overall antibacterial qualities of surfaces [55; 56; 57; 58]. It was established that the nano-/micro- scale characteristics of the substrate will affect the early stages of biofilm formation on metal surfaces, and influence the morphology of biofilms [58]. Regulation of surface nanotopography has been reported as a successful strategy to endow different materials with antibacterial properties [59; 60; 61; 62]. [PERSON] et al. developed a new superhydrophobic stainless steel surface by controlling nanostructures which reduced pathogenic bacteria adhesion [59]. [PERSON] et al. obtained aluminum substrates with a multiscale surface architecture by wet etching. While smooth surfaces killed 7% of _Escherichia coli_ and 3% of _Staphylococcus aureus_ cells, aluminum with multiscale surfaces killed 97% and 28%, respectively [60]. [PERSON] et al. reduced the adhesion of _Escherichia coli_ and _Staphylococcus aureus_ by altering the nanoroughness of nanostructured titanium surfaces, which were produced by physical vapor deposition [61]. Not limited to the above examples, plenty of studies have validated the hypothesis that antibacterial qualities correlate with nanostructured surfaces, which indicates that nanostructured surfaces are promising in their ability to reduce bacterial adhesion and biofilm formation [62; 63; 64]. Stainless steel (SS) is one of the most commonly used raw materials due to its physico-chemical stability, cleanability and economic benefits. However, biofilms on the surface of SS may lead to biofouling and biocorrosion, resulting in damage to SS structures in a wide variety of industrial sectors, including medical instruments, pipes, heat exchangers etc. [65; 66; 67; 68]; this brings public health concerns and environmental worries, alongside the economic loss. Thus, effective strategies to control bacterial adhesion and biofilm formation on the surface of SS are urgently needed. Nafion is a polymer of perfluoro-sulfonic acid developed from a variation of Teflon by Dupont Company, made from copolymerization groups of perfluoroalkyl sulfonyl fluoride with tetrafluoroethylene (TFE). The chemical structure of Nafion, as shown in Figure 1, has a hydrophobic tetrafluoroethylene backbone and perfluoronated vinyl-ethers terminated by sulfonic groups [69]. The hydrogen ion of the sulfonic acid groups of Nafion dissociates in solution, and the remaining polymers are negatively charged. In our previous study [70], we found that negatively charged SS surfaces with Nafion coating could reduce the _E. coli_ adhesion. However, this study only illustrated the efficiency of such surfaces for reducing the adhesion of _E. coli_, which is one kind of Gram-negative (G\({}^{-}\)) bacteria. In general, bacteria are divided into two kinds, according to the color that appears after Gram staining: Gram negative (G\({}^{-}\)) bacteria and Gram positive (G\({}^{+}\)) bacteria. Differences in bacterial cell envelopes contribute to color differences, and may also influence the antibacterial ability of antibacterial materials [71]. Therefore, the aim of this study is to investigate the antibacterial ability of a Nafion-coated SS surface on G\({}^{+}\) bacteria, and the role of surface properties on bacterial adhesion. _Bacillus subtilis_ (_B. subtilis_), which is a representative G\({}^{+}\) bacteria, was selected as a test organism. In this work, we report a facile way to modify the SS to be negatively charged via Nafion coating. The surface properties were characterized using a contact angle measuring instrument, laser scanning microscope (LSM) and scanning electron microscopy (SEM).