Chemical identification of differing amphiphiles in mixed Langmuir-Blodgett films by scanning surface potential microscopy

Chi, Lifeng; Jacobi, S.; Fuchs, Harald

doi:10.1016/s0040-6090(95)08352-9

Cited by 25 publications

(19 citation statements)

References 11 publications

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“…17 Surface potential is also very sensitive to surface chemical composition because the potential depends on the dielectric properties of the adsorbent on the sample surface. 18,19 During the polishing of the channel glass, particles of different materials may have adsorbed at the channel's rim and produced the strong surface-potential enhancement observed in the SSPM image.…”

Section: Resultsmentioning

confidence: 99%

Molecular Photovoltaics and Surface Potentials at the Air−Water Interface

et al. 2003

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An experimental approach that directly measures light-induced electrostatic surface potentials at the gasliquid interface using the combined techniques of the atomic force microscope and the scanning surfacepotential microscope is presented. Photosystem I (PSI) reaction centers, one of the molecular photovoltaic structures of green plants, convert light energy into electrical energy. We report the orientation and measurement of light-induced photovoltages at the air-water interface by PSI solutions entrained in the pores of microchannel glass. The data indicate that illuminated PSI reaction centers reversed the sign of the water surface electrostatic potential from negative to positive and that additional illumination further increased the positive value of the potential. The sign of the light-induced photopotentials indicates that the reaction centers are oriented with their electron-transport vectors pointing toward the water phase. Electrostatic potentials as a function of PSI concentration are presented for concentrations of active PSI up to 1 µM. Orienting biomolecules at the airwater interface might be an enabling technology for new classes of sensors.

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Section: Resultsmentioning

confidence: 99%

Molecular Photovoltaics and Surface Potentials at the Air−Water Interface

et al. 2003

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“…KPFM is an imaging mode of AFM and produces a map of the local electrical surface potential in addition to a topographical AFM image. For films of amphiphilic molecules, the electrical surface potential is a footprint of the molecular species and/or their molecular order under the tip (14)(15)(16)(17) and arises from the alignment of molecular dipoles m, upon packing of the film (18). More specifically, the surface potential is a function of the component of m normal to the interface, the dielectric constant e of the environment of the dipoles, and the packing density of molecules (dipoles) or surface area A occupied by each molecule.…”

Section: Introductionmentioning

confidence: 99%

An Elevated Level of Cholesterol Impairs Self-Assembly of Pulmonary Surfactant into a Functional Film

Leonenko

Gill

Baoukina

et al. 2007

Biophysical Journal

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In adult respiratory distress syndrome, the primary function of pulmonary surfactant to strongly reduce the surface tension of the air-alveolar interface is impaired, resulting in diminished lung compliance, a decreased lung volume, and severe hypoxemia. Dysfunction coincides with an increased level of cholesterol in surfactant which on its own or together with other factors causes surfactant failure. In the current study, we investigated by atomic force microscopy and Kelvin-probe force microscopy how the increased level of cholesterol disrupts the assembly of an efficient film. Functional surfactant films underwent a monolayer-bilayer conversion upon contraction and resulted in a film with lipid bilayer stacks, scattered over a lipid monolayer. Large stacks were at positive electrical potential, small stacks at negative potential with respect to the surrounding monolayer areas. Dysfunctional films formed only few stacks. The surface potential of the occasional stacks was also not different from the surrounding monolayer. Based on film topology and potential distribution, we propose a mechanism for formation of stacked bilayer patches whereby the helical surfactant-associated protein SP-C becomes inserted into the bilayers with defined polarity. We discuss the functional role of the stacks as mechanically reinforcing elements and how an elevated level of cholesterol inhibits the formation of the stacks. This offers a simple biophysical explanation for surfactant inhibition in adult respiratory distress syndrome and possible targets for treatment.

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“…LB films supported by solid substrates have been the subject of numerous scanning force microscopy (SFM) studies in recent years. − High-resolution images on barium arachidate multilayers show that SFM offers a unique method to resolve the different molecular lattices on the same sample . The SFM investigations of LB films transferred in the coexistence region of the liquid-condensed phase and the liquid-expanded (LE) phase, with one 14,15 or more different chemical components, , gave detailed information about the morphology, the mechanical properties, and the phase separation. The rich textures in LC domains observed by PFM and BAM at the air/water interface are not expected to be observed by SFM in topographical imaging, since the molecules in different segments only differ in their azimuthal angles and thus exhibit the same height.…”

Section: Introductionmentioning

confidence: 99%

Study of Long-Range Tilt Orientation in Fatty Acid Monolayers by Dynamic Scanning Force Microscopy

Gleiche

Fuchs

1998

Langmuir

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Segments in the liquid condensed (LC) domains of stearic acid, induced by long-range tilt orientation, were visualized on solid substrates by applying scanning force microscopy (SFM) using the force modulation mode (FMM). To understand the image contrast, a model based on the asymmetric apex of the SFM tip and the tilted phase of the molecules on the solid substrate after film transfer is presented. As a result, the apparent local elasticity is found to vary for molecules having the same tilt angle but different azimuthal angles. The observed textures are in good agreement with the theoretically predicted ones. IntroductionIn the past decade, liquid condensed (LC) domains formed during the transition from a liquid phase to a condensed phase in Langmuir monolayers were intensively investigated with respect to the long range tilt orientational order as related to their rich and defined textures. 1-8 Originally, the observations were done by polarized fluorescence microscopy (PFM). 1-3 Recently, Brewster angle microscopy (BAM) allowed the direct observation of tilted phases of various amphiphiles, including for example a fatty acid, 4 a fatty acid methyl ester, 5 a fatty acid ethyl ester, 6 and a 1-monoglyceride. 7,8 The textures of the ester monolayers often show "star" defects, 5,6 while the fatty acids show a "boojum" texture. 4 The observed textures can be predicted from the Landau free energy for tilted hexatic phases of monolayers, supplemented by a boundary energy. 9 These studies reveal that Langmuir monolayers often self-organize into structures in which the molecular azimuthal tilt is ordered over mesoscopic distances. 10 The textures are often similar to those observed in thin liquid crystal films. 11 These kinds of studies were concentrated on Langmuir monolayers at the air/water interface. Only a few investigations concerning these phenomena were done on LangmuirBlodgett films on solid substrates. 12 LB films supported by solid substrates have been the subject of numerous scanning force microscopy (SFM)

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Chemical identification of differing amphiphiles in mixed Langmuir-Blodgett films by scanning surface potential microscopy

Cited by 25 publications

References 11 publications

Molecular Photovoltaics and Surface Potentials at the Air−Water Interface

Molecular Photovoltaics and Surface Potentials at the Air−Water Interface

An Elevated Level of Cholesterol Impairs Self-Assembly of Pulmonary Surfactant into a Functional Film

Study of Long-Range Tilt Orientation in Fatty Acid Monolayers by Dynamic Scanning Force Microscopy

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