Nanoscale electric polarizability of ultrathin biolayers on insulating substrates by electrostatic force microscopy

• Published in: Nanoscale Vol. 7; no. 43; pp. 18327 - 18336
• Main Authors: Dols-Perez, A, Gramse, G, Calò, A, Gomila, G, Fumagalli, L
• Format: Journal Article
• Language: English
• Published: England 21.11.2015
• Subjects: Bacteriorhodopsin; Cholesterol - chemistry; Electric polarization; Electrically conductive; Electrostatics; Lipid Bilayers - chemistry; Mathematical models; Mica; Microscopy - methods; Nanostructure; Phosphatidylcholines - chemistry; Static Electricity; Substrates
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/c5nr04983k

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.