## 2 Applications of Biosensors in Bacteria Detection
### Strategies to Reduce and Control Bacterial Adhesion on Sensing Surfaces
Nevertheless, surface chemical inhomogeneity and morphological roughness, and the living nature of the system, may also need to be taken into account [220], as was already demonstrated in the case of proteins [102, 221]. It follows from the above discussion that screening the surface charge of a substratum directly changes the energy landscape of adhesion, provided ionic strength is low. Polymer-mediated interactions are not always repulsive, depending on the properties of the polymers and the solid surface [224]. The [PERSON] group studied resistant surface coatings of various self-assembled monolayers (SAM) with different head groups and found that surfaces terminated with derivatives of Sarc and \(N\)-acetylpiperazine resisted the adhesion of \(S\). _aureus_ and \(S\). _epidernidis_[225]. They used a commercial SPR biosensor to follow up the building of various SAMs on the gold sensor surface. These layers have been shown to resist protein adsorption in previous studies. The general hypothesis that protein-resistant layers also inhibit bacterial adhesion was examined. In summary, the authors found no correlation between the adsorption of protein (fibrinogen and lysozyme) and the adhesion of bacteria--unsurprisingly, since the outer surface of a bacterium is polysaccharide rather than proteinaceous. It is a general belief that bacteria attach more rapidly to hydrophobic surfaces such as polystyrene and Teflon than to hydrophilic materials such as glass. However, results in the literature showed a more complex behavior and there are other important factors beside surface energy [226]. An important class of chemicals, namely the poly(ethylene glycol)s, has been used to modify surfaces with the aim of reducing bacterial attachment, based on this compound's known high mobility and extremely large exclusion volumes [227]. It was found that poly(ethylene glycol) significantly reduced surface hydrophobicity and indeed reduced the attachment of \(S\). _epidernidis_ and \(E\). _coli_ by up to 2 log CFU/mL [228]. In another study, [PERSON] and co-workers covalently coated glass surfaces with poly(ethylene oxide)  
Figure 2: On the left: schematic illustration and the list of the parameters that affect the initial attachment of bacterial cells to a solid–liquid interface (in case of the bacterium, liquid medium and substratum [222, 223]). On the right: plotted DLVO and extended DLVO (XDLVO) force graphs based on the figure of [PERSON] et al. [216], van der Waals force (dashed line), and electrostatic repulsion curves are also shown. V/KT represents the potential energy (V) divided by Boltzmann’s constant (K) and absolute temperature (T) [216]. brushes and demonstrated a reduction in the attachment of five bacterial and two yeast strains [229]. Covalent functionalization of glass with poly(4-vinyl-\(N\)-alkylpyridinium bromide) (a polycation material that has been reported to kill bacteria) can reduce the attachment of 1-2 log of _S. aureus_, _S. epidermidis_, _P. aeruginosa_, and _E. coli_ on the surface [230]. In a seminal paper, [PERSON] and co-workers applied a combinatorial chemistry approach for bacteria-resistant polymer surfaces [231]. They generated a large combinatorial space from a library of 22 acrylate monomers including ethylene glycol chains of various lengths, fluoro-substituted alkanes, linear and cyclic aliphatic, aromatic, and amine moieties. The combined monomer solutions were printed onto a poly (hydroxyl ethylmethacrylate) (pHEMA)-coated microscope slide to form a combinatorial polymer microarray. High-throughput surface characterization of microarrays was carried out to investigate the effect of polymer surface properties on bacterial attachment. The microarray was incubated with _P. aeruginosa_, _S. aureus_, and uropathogenic _E. coli_ (UPEC) with plasmids expressing GFP (green fluorescent protein) and read by a fluorescent scanner.