silicon and decane

Nano-BLMs (black lipid membranes) suspending the pores of highly ordered porous silicon substrates have been proven useful for functional investigations of ion channel proteins by electrical readouts. With the aim to monitor the resistive behavior of nano-BLMs spatially resolved in a contact-free manner, we report here on the visualization of nano-BLMs by means of scanning ion conductance microscopy (SICM). Silicon surfaces with highly ordered pore arrays were coated with a gold layer and functionalized with octadecanethiol before a droplet of 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) (2% w/v) dissolved in n-decane was applied. The topography of DPhPC membranes suspending the pores was stably imaged for hours without mechanical contact using SICM. This suggests that SICM provides a significant advantage over atomic force microscopy, where mechanical interactions occur that easily damage the suspended membranes. Dynamic processes such as spreading and rupturing of membranes were spatially and temporally resolved. Furthermore, SICM was used to individually manipulate membranes suspending single pores, thereby writing lithographic patterns into the lipid. The process of local membrane manipulation was correlated to a characteristic signature in the simultaneously recorded ion current. The results show that SICM is well-suited both for contact-free imaging of soft suspended membranes and for local membrane manipulation.

Topics: Alkanes; Cations; Chemistry; DNA; Electrodes; Equipment Design; Ions; Lipid Bilayers; Lipids; Membranes; Microscopy, Atomic Force; Microscopy, Electron, Scanning; Phosphatidylcholines; Silicon; Synchrotrons

This paper presents the first functionalization of silicon surfaces with well-defined, covalently attached monolayers containing saccharides. Two methods were used to this aim: a thermal method (refluxing in mesitylene) and a recently developed, extremely mild photochemical method (irradiation with 447 nm at room temperature). The results were analyzed by FT-IR and angle-resolved X-ray photoelectron spectroscopy. The use of a two-dimensional detector in ARXPS allows for unparalleled, subnanometer resolution in the determination of the elemental composition of monolayers. Even for monolayers with a total thickness of only approximately 1.5 nm, a clear elemental depth profile can be obtained. Such analyses display for sialic acid-containing monolayers that the mild photochemical attachment does not destroy the (rather fragile) sialic acid moiety and that the sugar is present at the top of the monolayer and thus available for biological interactions.

Topics: Alkanes; Alkenes; Monosaccharides; Silicon; Spectrometry, X-Ray Emission; Spectrophotometry, Infrared; Surface Properties