Neutron Reflectivity and Atomic Force Microscopy Studies of a Lipid Bilayer in Water Adsorbed to the Surface of a Silicon Single Crystal Export

@article{citeulike:1614930, abstract = {Abstract: Specular reflection of neutrons has been used to characterize the structure of single lipid bilayers adsorbed to a planar silicon surface from aqueous solution. We used a novel experimental setup which significantly decreased the incoherent background scattering and allowed us to measure neutron reflectivities as low as 5 × 10-7. Thicknesses and neutron scattering length densities were determined by a fitting procedure using (i) randomly generated smooth functions represented by parametric B-splines and (ii) stepped functions based on the theoretical lipid composition. The size of lipid domains at the surface and the degree of surface coverage were determined by atomic force microscopy. Chain-protonated and -deuterated dipalmitoylphosphatidylcholine (DPPC) bilayers were investigated in 2H2O and a mixture of 2H2O and H2O which matches the scattering density of silicon. Also, one measurement on a distearoylphosphatidylcholine bilayer which has longer acyl chains was performed for comparison. The lipid adsorbs to the silicon surface as a continuous layer interrupted by irregularly shaped uncovered areas which are 100-500 \r{A} in size. The surface coverage was estimated to be 70 ± 20\%. The reflectivity measurements on DPPC at 60 C show a silicon oxide layer with a thickness of the order of 4 \r{A}, a rough silicon oxide/water layer between silicon oxide and lipid with a thickness between 2 and 8 \r{A}, and a single lipid bilayer. Fitting resolved a central membrane layer with a thickness of 28 ± 2 \r{A} which represents the lipid hydrocarbon chains. This layer is sandwiched between interface membrane layers of lipid head groups and water which are 11.5 ± 1 \r{A} in thickness. The angstrom-scale thickness changes of the central membrane layer as a function of the phase state of the lipid and of the length of the hydrocarbon chains are easily detected.}, address = {Laboratory of Biophysical Chemistry, NHLBI, NIH, Bethesda, Maryland 20892-1676, Materials Science and Engineering Laboratory, NIST, Gaithersburg, Maryland 20899-0001, and Laboratory of Membrane Biochemistry and Biophysics, NIAAA, NIH, 12501 Washington Avenue, Rockville, Maryland 20852}, author = {Koenig, B. W. and Krueger, S. and Orts, W. J. and Majkrzak, C. F. and Berk, N. F. and Silverton, J. V. and Gawrisch, K.}, citeulike-article-id = {1614930}, citeulike-linkout-0 = {http://dx.doi.org/10.1021/la950580r}, citeulike-linkout-1 = {http://pubs.acs.org/doi/abs/10.1021/la950580r}, day = {6}, doi = {10.1021/la950580r}, journal = {Langmuir}, keywords = {adsorption, afm, atomic, bilayers, crystal, force, lipid, membranes, microscopy, neutron, reflection, silicon, surface, water}, month = {March}, number = {5}, pages = {1343--1350}, posted-at = {2007-09-03 03:01:40}, priority = {2}, title = {Neutron Reflectivity and Atomic Force Microscopy Studies of a Lipid Bilayer in Water Adsorbed to the Surface of a Silicon Single Crystal}, url = {http://dx.doi.org/10.1021/la950580r}, volume = {12}, year = {1996} }

TY - JOUR ID - citeulike:1614930 L3 - citeulike-article-id:1614930 N2 - Abstract: Specular reflection of neutrons has been used to characterize the structure of single lipid bilayers adsorbed to a planar silicon surface from aqueous solution. We used a novel experimental setup which significantly decreased the incoherent background scattering and allowed us to measure neutron reflectivities as low as 5 × 10-7. Thicknesses and neutron scattering length densities were determined by a fitting procedure using (i) randomly generated smooth functions represented by parametric B-splines and (ii) stepped functions based on the theoretical lipid composition. The size of lipid domains at the surface and the degree of surface coverage were determined by atomic force microscopy. Chain-protonated and -deuterated dipalmitoylphosphatidylcholine (DPPC) bilayers were investigated in 2H2O and a mixture of 2H2O and H2O which matches the scattering density of silicon. Also, one measurement on a distearoylphosphatidylcholine bilayer which has longer acyl chains was performed for comparison. The lipid adsorbs to the silicon surface as a continuous layer interrupted by irregularly shaped uncovered areas which are 100-500 Å in size. The surface coverage was estimated to be 70 ± 20%. The reflectivity measurements on DPPC at 60 C show a silicon oxide layer with a thickness of the order of 4 Å, a rough silicon oxide/water layer between silicon oxide and lipid with a thickness between 2 and 8 Å, and a single lipid bilayer. Fitting resolved a central membrane layer with a thickness of 28 ± 2 Å which represents the lipid hydrocarbon chains. This layer is sandwiched between interface membrane layers of lipid head groups and water which are 11.5 ± 1 Å in thickness. The angstrom-scale thickness changes of the central membrane layer as a function of the phase state of the lipid and of the length of the hydrocarbon chains are easily detected. IS - 5 JF - Langmuir AD - Laboratory of Biophysical Chemistry, NHLBI, NIH, Bethesda, Maryland 20892-1676, Materials Science and Engineering Laboratory, NIST, Gaithersburg, Maryland 20899-0001, and Laboratory of Membrane Biochemistry and Biophysics, NIAAA, NIH, 12501 Washington Avenue, Rockville, Maryland 20852 EP - 1350 TI - Neutron Reflectivity and Atomic Force Microscopy Studies of a Lipid Bilayer in Water Adsorbed to the Surface of a Silicon Single Crystal VL - 12 SP - 1343 KW - adsorption KW - afm KW - atomic KW - bilayers KW - crystal KW - force KW - lipid KW - membranes KW - microscopy KW - neutron KW - reflection KW - silicon KW - surface KW - water AU - Koenig, BW AU - Krueger, S AU - Orts, WJ AU - Majkrzak, CF AU - Berk, NF AU - Silverton, JV AU - Gawrisch, K PY - 1996/03/06/ UR - http://dx.doi.org/10.1021/la950580r ER -