Dols-Perez…Fumagalli {Nanoscale 7: 18327}
Topography and dielectric image (capacitance gradient) of a bacteriorhodopsin monolayer patch, 5.3 nm thick on a mica substrate. By combining information from the two images the dielectric constant of the protein layer can be determined with nanoscale lateral spatial resolution
Nanoscale electric polarizability of ultrathin biolayers on insulating substrates by electrostatic force microscopy
Dols-Perez A, Gramse G, Calò A, Gomila G, Fumagalli L.
Nanoscale 2015 Oct; 7: 18327.
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.
PubMed: 26488226. Doi: 10.1039/c5nr04983k
