KPFM and PFM of Biological Systems

Abstract

Surface potentials and electrostatic interactions in biological systems are key elements of cellular regulation and interaction. Examples include cardiac and muscular activity, voltage-gated ion channels, protein folding and assembly, and electroactive cells and electrotransduction. The coupling between electrical, mechanical, and chemical signals and responses in cellular systems necessitates the development of tools capable of measuring the distribution of charged species, surface potentials, and mechanical responses to applied electrical stimuli and vice versa, ultimately under physiological conditions. In this chapter, applications of voltage-modulated atomic force microscopy (AFM) methods including Kelvin probe force microscopy (KPFM) and piezoresponse force microscopy (PFM) to biological systems are discussed. KPFM is a force-sensitive non-contact or intermittent-contact mode AFM technique that allows electrostatic interactions and surface potentials to be addressed. Beyond long-range electrostatic interactions, the application of bias can lead to a mechanical response, e.g., due to linear piezoelectric coupling in polar biopolymers or via more complex electrotransduction and redox pathways in other biosystems. The use and development of PFM, based on direct electromechanical detection, to biological systems will also be addressed. The similarities and limitations of measuring surface potentials and electromechanical coupling in solution will be outlined.KeywordsElectromechanical CouplingPurple MembranePiezoresponse Force MicroscopyKelvin Probe Force MicroscopyHighly Order Pyrolytic GraphiteThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.