The formation of supported lipid bilayers (SLBs) on glass from giant unilamellar vesicles (GUVs) was studied using fluorescence microscopy. We show that GUV rupture occurs by at least four mechanisms, including 1), spontaneous rupture of isolated GUVs yielding almost heart-shaped bilayer patches (asymmetric rupture); 2), spontaneous rupture of isolated GUVs yielding circular bilayer patches (symmetric rupture); 3), induced rupture of an incoming vesicle when it contacts a planar bilayer edge; and 4), induced rupture of an adsorbed GUV when a nearby GUV spontaneously ruptures. In pathway 1, the dominant rupture pathway for isolated GUVs, GUVs deformed upon adsorption to the glass surface, and planar bilayer patch formation was initiated by rupture pore formation near the rim of the glass-bilayer interface. Expanding rupture pores led to planar bilayer formation in approximately 10-20 ms. Rupture probability per unit time depended on the average intrinsic curvature of the component lipids. The membrane leaflet adsorbed to the glass surface in planar bilayer patches originated from the outer leaflet of GUVs. Pathway 2 was rarely observed. We surmise that SLB formation is predominantly initiated by pathway 1 rupture events, and that rupture events occurring by pathways 3 and 4 dominate during later stages of SLB formation.

The adsorption of large unilamellar vesicles composed of various combinations of phosphatidylcholine, phosphatidylethanolamine (PE), monomethyl PE, and dimethyl PE (PE-Me2) onto a glass surface was studied using fluorescence microscopy. The average lipid geometry within the vesicles, described mathematically by the average intrinsic curvature, C(0,ave), was methodically altered by changing the lipid ratios to determine the effect of intrinsic curvature on the ability of vesicles to rupture and form a supported lipid bilayer. We show that the ability of vesicles to create fluid planar bilayers is dependent on C(0,ave) and independent of the identity of the component lipids. When the C(0,ave) was approximately -0.1 nm(-1), the vesicles readily formed supported lipid bilayers with almost full mobility. In contrast, when the C(0,ave) ranged from approximately -0.2 to approximately -0.3 nm(-1), the adsorbed vesicles remained intact upon the surface. The results indicate that the average shape of lipid molecules within a vesicle (C(0,ave)) is essential for determining kinetically viable reactions that are responsible for global geometric changes.

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DNA oligomers deposited on Cu(111) surfaces were observed at liquid nitrogen temperature using a scanning tunneling microscope. The observed oligomers were pAAAAAAATTTTTTT (14mer), pTTTGGTTAACCAAA (14mer), pGGGGGTTTTTTTTTT (15mer), and pAAAAAAAAAATTTTTTTTTT (20mer). The structure of the isolated oligomers adsorbed on the Cu surface varies with the length of the molecular chain. The isolated 20mer is adsorbed to aggregate three-dimensionally. The isolated 14mer and 15mer are extended on the surface, and the almost entire molecular chain touches the surface. A highly resolved image of the 20mer shows bright spots aligned in a row along a single-stranded DNA with the same periodicity as that of the nucleotide units, demonstrating that each bright spot is a nucleotide.

Articles you may be interested inAtomic resolution imaging of a single-crystal Cu (100) surface by scanning tunneling microscopy in ultrahigh vacuum at room temperature Direct comparisons of rates for low temperature diffusion of hydrogen and deuterium on Cu(001) from quantum mechanical calculations and scanning tunneling microscopy experimentsThe role of adsorbed alkali metal atoms in the enhancement of surface reactivity: A scanning tunneling microscopy study of low coverage K/Si (111)7×7 surfacesThe surface structures of DNA oligomers, pAAAAAAATTTTTTT, deposited on Cu͑111͒ surface have been characterized at liquid nitrogen temperature using a scanning tunneling microscope. Four different types of adsorbed structures have been observed in DNA oligomers; ͑i͒ an isolated whole molecule, ͑ii͒ a shortened molecule, ͑iii͒ a cluster, and ͑iv͒ a double helix. The internal structures of the oligomers also have been resolved.

We demonstrated developments of a non-labeling DNA (deoxyribonucleic acid) sensor by using a commercially available ion-sensitive field-effect transistor (IS-FET). A single strand DNA was immobilized on a Ta2O5 thin film on a gate electrode in the IS-FET, and the surface of the thin film was confirmed by XPS measurements. The results indicated that the DNA was immobilized on the Ta2O5 thin film. To detect the hybridization of DNA, we carried out measurements of I drain-V gs properties of IS-FETs immobilized by ss-DNA and ds-DNA hybridized by complemental target DNA. Then, the difference in threshold voltage was evaluated to be about 10 mV, and the amount of immobilized DNA as 6.3×107 [molecules/cm2]. Consequently, the non-labeling IS-FET DNA sensor is expected to be a novel measurement tool for diagnosing diseases.

Bleiben oder gehen? Die Produktverteilung für an die Si(001)‐Oberfläche adsorbiertes Aceton kann durch Erhöhung der Oberflächentemperatur von kinetisch kontrolliert (Vierring‐Spezies; siehe Schema) nach thermodynamisch kontrolliert (Dissoziations‐Spezies) verschoben werden. Damit ist gezeigt, dass organische Moleküle an die Si(001)‐Oberfläche reversibel binden.