Self-Assembled Molecular Platforms for Bacteria/Material Biointerface Studies: Importance to Control Functional Group Accessibility

Highly controlled mixed molecular layers are crucial to study the role of material surface chemistry in biointerfaces, such as bacteria and subsequent biofilms interacting with biomaterials. Silanes with non-nucleophilic functional groups are promising to form self-assembled monolayers (SAMs) due to their low sensitivity to side-reactions. Nevertheless, the real control of surface chemistry, layer structure, and organization has not been determined. Here, we report a comprehensive synthesis and analysis of undecyltrichlorosilane- and 11-bromoundecyltrichlorosilane-based mixed SAMs on silicon substrates. The impact of the experimental conditions on the control of surface chemistry, layer structure, and organization was investigated by combining survey and high-resolution X-ray photoelectron spectroscopy analysis, wettability measurements, and ellipsometry. The most appropriate conditions were first determined for elaborating highly reproducible, but easily made, pure 11-bromoundecyltrichlorosilane SAMs. We have demonstrated that the control is maintained on more complex surfaces, i.e., surfaces revealing various chemical densities, which were obtained with different ratios of undecyltrichlorosilane and 11-bromoundecyltrichlorosilane. The control is also maintained after bromine to amine group conversion via S_N2 bromine-to-azide reactions. The appropriateness of such highly controlled amino- and methyl-group revealing platforms (NH₂–<i>X</i>%/CH₃) for biointerface studies was shown by the higher reproducibility of bacterial adhesion on NH₂–100%/CH₃ SAMs compared to bacterial adhesion on molecular layers of overall similar surface chemistry but less control at the molecular scale