Self-Assembled
Molecular Platforms for Bacteria/Material Biointerface Studies: Importance
to Control Functional Group Accessibility
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Abstract
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<sub>N</sub>2 bromine-to-azide
reactions. The appropriateness of such highly controlled amino- and
methyl-group revealing platforms (NH<sub>2</sub>–<i>X</i>%/CH<sub>3</sub>) for biointerface studies was shown by the higher
reproducibility of bacterial adhesion on NH<sub>2</sub>–100%/CH<sub>3</sub> SAMs compared to bacterial adhesion on molecular layers of
overall similar surface chemistry but less control at the molecular
scale