Reversible functionalization of germanium by thiol monolayers to probe protein / surface interactions by ATR-FTIR

The functionalization of germanium by SAMs is commonly used to passivate the surface and thus prevent its oxidation. This functionalization can also be very useful to study specific interactions for instance in biosensors using protein or enzyme recognition. Several functionalization methods exist but no method has up to now been described to regenerate the Ge surface. A procedure for regenerating the surface of Ge after functionalization by SAMs is proposed in this article. The characterization of the functionalized and regenerated Ge surface by contact angle, XPS and ATR-FTIR, allows to establish that the protocol is robust. Hydrophilic SAMs (HS-(CH2)n-COOH, HS-(CH2)n-OH) and hydrophobic SAMs (HS-(CH2)n-CH3) of different chain lengths (n = 5 or 10) were tested. After ten cycles of functionalization and regeneration, the surface of germanium presents the same wettability, with a small decrease in its oxidation state. As an example of interest, this method allows to study the structure of a protein adsorbed on biomimetic surfaces (SAM type) by ATR-FTIR with a reusable commercial Ge crystal following the elimination of SAMs with a process retaining the native properties of the Ge.