In Situ Monitoring Of Alkanethiol Self-Assembly Onto Zinc Selenide: The Role Of Substrate Pretreatment And Its Implication In Bacterial Attachment

The interface between pioneer sessile bacteria and a supporting substrate can be probed in situ and at the molecular scale by infrared spectroscopy in the attenuated total reflection mode (ATR-FTIR). Here, a self-assembled monolayer (SAM) of amino-terminated alkanethiol is formed on the internal reflection element (IRE) composed of zinc selenide, and the attachment of model bacteriumLactobacillus rhamnosusGG (LGG) is subsequently studied. The impact of the beforehand surface preparation of the IRE on the SAM is studied on ZnSe substrates (i) cleaned by exposure to ozone/UV, (ii) acid cleaned, or (iii) coated with a thin gold film. The surface properties of the obtained substrates are analyzed by atomic force and electron microscopies, and elastic ion backscattering spectrometry. The kinetics of the formation and the organization of the formed SAMs are strongly surface dependent, as evidenced with ATR-FTIR. Acid-cleaned and gold-coated IREs are the least and most favorable substrates for alkanethiol SAM formation, respectively. Regardless of differences in SAM properties, the average degree of LGG attachment is similar on all functionalized substrates. The molecular organization of LGG cells, however, is substrate-dependent suggesting a possible effect of SAM organization on the bacteria-substrate interface.