Nanoscale electric polarizability of ultrathin biolayers on insulating substrates by electrostatic force microscopy.
We measured and quantified the local electric polarization properties of ultrathin (∼5 nm) biolayers on mm-thick mica substrates. We achieved it by scanning a sharp conductive tip (<10 nm radius) of an electrostatic force microscope over the biolayers and quantifying sub-picoNewton electric polarization forces with a sharp-tip model implemented using finite-element numerical calculations. We obtained relative dielectric constants εr = 3.3, 2.4 and 1.9 for bacteriorhodopsin, dioleoylphosphatidylcholine (DOPC) and cholesterol layers, chosen as representative of the main cell membrane components, with an error below 10% and a spatial resolution down to ∼50 nm. The ability of using insulating substrates common in biophysics research, such as mica or glass, instead of metallic substrates, offers both a general platform to determine the dielectric properties of biolayers and a wider compatibility with other characterization techniques, such as optical microscopy. This opens up new possibilities for biolayer research at the nanoscale, including nanoscale label-free composition mapping.
Institut de Química Avançada de Catalunya (IQAC-CSIC), C/Jordi Girona 18-26, 08034, Barcelona, Spain and CIBER of Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Barcelona, Spain.
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Dols-Perez
Johannes Kepler University Linz, Institute for Biophysics, Gruberst. 40, 4020-Linz, Austria.
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Gramse
CIC NanoGUNE Consolider, E-20018 Donostia San Sebastian, Spain.
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Calò
Nanobioelec group, Institut de Bioenginyeria de Catalunya (IBEC), Baldiri i Reixac 15-21, 08028-Barcelona, Spain and Departament d'Electrònica, Universitat de Barcelona, C/Martí i Franquès 1, 08028 Barcelona, Spain.
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Gomila
School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL, UK. laura.fumagalli@manchester.ac.uk.
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Fumagalli
D002784:Cholesterol / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008853:Microscopy / Q000379:methods*; D010713:Phosphatidylcholines / Q000737:chemistry*; D055672:Static Electricity
D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D002784:Cholesterol; C017251:1,2-oleoylphosphatidylcholine