## 1 Introduction
One such electrokinetic phenomena which allows the analysis of the preferential formation and growth of biofilms within microfluidic devices is dielectrophoresis (DEP), which relies on the control of electrically neutral particles. When suspending such particles or cells in a non-uniform electric field, they will be polarized into dipoles, and the net force acting upon them will drive the particles or cells towards a high field gradient region (positive DEP) or push away from it (negative DEP) [21; 22]. Bacterial biofilms are structured communities of bacterial cells surrounded by an extracellular (polymeric) matrix (ECM) that firmly attach to biotic or abiotic surfaces [23]. The aggregation, or cell-cell interaction, can occur both in surface-attached biofilms, where one layer of the multi-layered biofilm interacts with a substratum, or in flocs, otherwise considered mobile biofilms. Either way, there is a clear distinction in their behaviour, compared to free-living bacterial cells, as a result of the social and physical interactions occurring between the cells and the ECM [24]. The ECM represents a three-dimensional scaffold-like structure responsible for the adhesion of the biofilm to surfaces, providing mechanical stability and complex microenvironments essential for the biofilm lifestyle [25; 26]. It is a predominantly aqueous medium containing structural and functional components [24]both soluble, such as gel-forming polysaccharides [25] and proteins, as well as insoluble, such as amyloids [27], cellulose [28], fimbiae, pili and flagella [27]. Besides the various proteins from the extracellular matrix (ECM), there are also proteoglycans and glycoproteins that are secreted locally and assembled into a spatially organized architecture in close association with the surface of the cells that produced them [29]. Each of the biofilm formation and growth stages is influenced and governed by different environmental factors. For biofilms growing on a substratum, the first step in the formation process is the adherence of the planktonic microorganisms to a surface, which is strongly determined by the surface quality of the substratum [30], and the existence of surface proteins such as SadB or LapA on the substratum [31]. This stage is followed by the development of microcolonies, the secretion of the extracellular polymeric matrix, and the development of a three-dimensional biofilm community, phases influenced by aerobic/anaerobic environmental conditions [32], temperature and shear stress [33]. The last step is the detachment of the microorganisms and their dissemination into the environment, the stage dependent on cell motility and ECM degradation, as well as on physical factors, such as the shear force [31,34,35]. An example of Gram-positive cocci involved in a wide variety of human infections and known for its ability to successfully develop biofilms on both biotic and abiotic surfaces [36,37] includes Staphylococcus aureus. Usually, Staphylococcus aureus produces a complex biofilm structure with multiple layers of glycocalyx [37]. In addition, the Staphylococcus aureus extracellular matrix has a fibrous structure [29], similar to that of fibrils/microfibrils structure type, containing nanocellulose fibre from biofilm of _Komagataebacter hansenii_[30]. The adhesion and maturation of biofilm are usually correlated with the production of an antigen responsible for adhesion, known as polysaccharide intercellular antigen (PIA). The synthesis of PIA starts from UDP-N-acetylglucosamine and is mediated by the products of the intercellular adhesion locus [38]. The interaction of these with different electric potentials has not yet been studied to our knowledge. Thus, this study provides the first insight into the interaction between the first steps in biofilm formation, adhesion, and formations of microcolonies, at different electric potentials.