Necessity of a Thorough Characterization of Functionalized Silicon Wafers before Biointerface Studies

Functionalized self-assembled monolayer (SAM) surfaces are frequently used for biological applications. Description of such surfaces is crucial to well-understand surface reactions and to achieve further controlled grafting. However, the difference between ideal (i.e., expected) and real molecular layers is often disregarded. This paper shows a systematic demonstration that thorough characterization and analysis of such layers are necessary for reaching the description of the real surface. Several model surfaces, with SAMs as the basis, were prepared and analyzed. Two steps of the characterization were distinguished. The first step involves commonly used measurements (X-ray photoelectron spectroscopy (XPS), survey spectra, static water-contact angle, atomic force microscopy (AFM) images) that were shown to lead to partial surface description. In the second step, additional measurements (XPS high-resolution spectra, water-contact angle hysteresis, AFM images, zeta potential) were allowed to highlight the modifications related to each grafting step and the morphological and conformational specificities (in particular defects) of the final surfaces.