Lipid bilayer functionalization of multiwalled carbon nanotubes

Integration of the technologically favorable mechanical and electrical properties of carbon nanotubes (CNTs) with the specific recognition properties of proteins could enable the development of novel bioelectronic, in particular biosensing, applications. The hydrophobic graphene surface of CNTs, however, is not a biological substrate and as-synthesized CNTs aggregate in aqueous solution. CNTs can be easily dispersed by non-covalent binding of surfactants like sodium dodecyl sulfate, but the use of such detergents is undesirable because they unfold proteins and degrade cell membranes. We show here that carbon nanotubes can also be dispersed by coating them with biocompatible surfactant analogs. Incubation of multiwalled CNTs with sonicated vesicles of synthetic phospholipids resulted in a stable aqueous suspension of the nanotubes, also after removal of the vesicles by centrifugation. When the vesicles were doped with a fluorescently labelled lipid, the washed CNTs could be observed by fluorescence microscopy. Additionally, atomic force microscopy indicated that the nanotubes were coated by a smooth layer, with occasional defects or transitions to a second layer. These discontinuities were consistently 4-5 nm deep, the typical thickness of a lipid bilayer. It can thus be concluded that vesicle fusion results in the formation of lipid bilayers on the surface of multiwalled CNTs. We addressed the influence of vesicle size, lipid acyl chain saturation, lipid head group charge, CNT surface modification, and CNT diameter on the efficiency of lipid coating. Significantly, it proved possible to include a fluorescently labelled transmembrane peptide in nanotube-supported bilayers, and we are currently investigating whether this can also be achieved for membrane protein

Direct mapping of the solid–liquid adhesion energy with subnanometre resolution

Solid–liquid interfaces play a fundamental role in surface electrochemistry1, catalysis2, wetting3, self-assembly4 and biomolecular functions5. The interfacial energy determines many of the properties of such interfaces, including the arrangement of the liquid molecules at the surface of the solid. Diffraction techniques are often used to investigate the structure of solid–liquid interfaces6, but measurements of irregular or inhomogeneous interfaces remain challenging. Here, we report atomic- and molecular-resolution images of various organic and inorganic samples in liquids, obtained with a commercial atomic force microscope operated dynamically with small-amplitude modulation. This approach uses the structured liquid layers close to the solid to enhance lateral resolution. We propose a model to explain the mechanism dominating the image formation, and show that the energy dissipated during this process is related to the interfacial energy through a readily achievable calibration curve. Our topographic images and interfacial energy maps could provide insights into important interfaces

Beta-sheet structured oligomers of Alzheimer's beta-amyloid peptide perturb phosphatidylcholine model membranes

31st Congress of the Federation-of-European-Biochemical-Societies (FEBS) Istanbul, TURKEY, JUN 24-29, 2006 : meeting abstractsThe response of Krebs cycle dehydrogenases to Ca2+ in physiological concentration range is well established, but little is known about Ca2+ overload induced changes in the activity of essential mitochondrial dehydrogenases. We examined whether very fast decrease in the amount of mitochondrial NAD(P)H under condition of Ca2+ overload may be caused by inhibition of Ca2+ sensitive NAD(P)-dependent dehydrogenases. Ca2+ overload (increase in extramitochondrial Ca2+ concentration from 1 lM to 10 and 30 lM) did not change the activity of mitochondrial pyruvate and 2-oxoglutarate dehydrogenases. Ca2+ inhibited NADP-dependent isocitrate dehydrogenase (ICDH) by 12% at 10 lM and 20% at 30 lM Ca2+ at subsaturating concentration of substrate. NAD-dependent ICDH was activated (21%) by increase of Ca2+ concentration from 1 lM to 10 lM. At saturating substrate concentration Ca2+ had not effect on the activity of NADP-dependent ICDH but NAD-dependent ICDH was activated: activity was higher by 43% at 10 lM Ca2+ in comparison to that at 5 nM; further increase in Ca2+ concentration did not affect the activity. The activity of NADP-ICDH was 100–350- fold higher than NAD-ICDH and increase in Ca2+ concentration substantially decreased the ratio of NADP-ICDH vs. NADICDH activity. The fact that supra-physiological Ca2+ levels moderately inhibit only NADP-ICDH cannot provide explanation for Ca2+ overload induced NAD(P)H depletion and inhibition of respiration in heart mitochondriaGamtos mokslų fakultetasKauno medicinos universitetasVytauto Didžiojo universiteta