Fluid Electric Force Microscopy for Charge Density Mapping in Biological Systems

Abstract

Electric force microscopy has been adapted for mapping surface charge density in aqueous solutions. The electric double layer interaction between the tip and the sample provides a contrast mechanism sensitive only to the surface charge density as other parameters are held constant. The resulting charge maps are acquired at typical atomic force microscopy scanning rates and approximately 25-nm resolution. The contrast is well-described by a simple expression for the tip-sample double layer interaction in electrolyte solutions. Fluid electric force microscopy is highly sensitive and nondestructive, as demonstrated with charge density maps of fluid-phase-supported bilayer membranes and single DNA molecules.

Visualizing the Path of DNA through Proteins Using DREEM Imaging

“…At present, we have not been able to identify operating parameters that allow contrast in aqueous environment. A few studies demonstrate EFM imaging of solid materials at low ionic strength using lift mode (Gramse et al, 2012; Johnson et al, 2003); however, the resolution and detection limit in these images appears low. It is likely that the electrostatic double layer significantly damps the DREEM signals from proteins and DNA in electrolyte solutions.…”

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…Therefore they take isoforce images at different salt concentrations to remove topography and isolate electrostatic contributions to the tip-sample interaction. A similar procedure was also used by Hafner et al [465].…”

Quantitative Nanoscale Dielectric Microscopy of Single-Layer Supported Biomembranes

“…18,19 Electrical SPM has also been widely used in the high-frequency domain. [20][21][22][23][24] Despite the variety of available SPM techniques, some of them already applied in the study of biological membranes, [25][26][27][28] the quantification of the low-frequency dielectric constant of biomembranes at the nanoscale has not been achieved yet.…”