In situ ATR FTIR monitoring of the formation of functionalized mono- and multilayers on germanium substrate: from 7-octenyltrichlorosilane to 7-carboxylsilane.

The development and optimization of biomimetic surfaces required for biosensors and medical assays are made more efficient by quantitatively monitoring the surface chemical reactions in situ by means of attenuated total reflection (ATR) FTIR spectroscopy. single-beam-sample-reference (SBSR) ATR, as well as modulated excitation (ME), techniques have been applied to get physicochemical information on growth and structure of the surface layer. SBSR and ME methods result in optimum background compensation and signal-to-noise ratio. Surface modification was performed on a germanium multiple internal reflection element (Ge-MIRE). Activation of the surface resulted in free Ge-OH groups used for a spontaneous chemical reaction with 7-octenyltrichlorosilane (7-OTCS) in toluene. Formation of Ge-O-Si bonds was enabled by hydrolization of Si-Cl3 after partial elimination of a tightly bound thin water layer covering the MIRE. Unwanted side-reaction by hydrolization of Si-Cl3 in solution followed by polymerization paralleled this process. Steady growing of the silane layer to multilayer thickness with increasing time was observed in all experiments. Most unexpectedly, in some experiments the end-standing double bond of the silane layer was found to be partly oxidized even after being exposed only to toluene, probably because of catalysis by molecular sieve nanoparticles remaining in toluene after drying. Finally, theoretical means are presented enabling the calculation of the spectrum of dissolved 7-OTCS in toluene, a prerequisite for background compensation during in situ studies of the growing layer.