Electromechanical imaging of biological systems with sub-10 nm resolution

Piezoelectricity in calcified and connective tissues has been known for over half a century following seminal works by Fukada. Traditionally, complex hierarchical structure of these materials, spanning the length scales from nanometers to millimeters, precluded quantitative studies, and hence elucidation of biological significance of biopiezoelectricity. Here, we demonstrate an approach for electromechanical imaging of structure of biological samples on the length scales from tens of microns to nanometers using piezoresponse force microscopy (PFM). In this method, intrinsic piezoelectricity of biopolymers such as proteins and polysaccharides is the basis for high-resolution imaging. Nanostructural imaging of a variety of protein-based materials, including tooth, antler, and cartilage is demonstrated. Visualization of protein fibrils with sub-10 nm spatial resolution in a human tooth is achieved. Given the near-ubiquitous presence of piezoelectricity in biological systems, PFM is suggested as a versatile tool for micro- and nanostructure imaging in both connective and calcified tissues. In the second part of the talk, I discuss recent advances in bioPFM, including imaging in liquid environments, resonance-enhanced PFM, and electrically shielded probes required to probe a broad range of electrophysiological processes from membrane flexoelectricity to cardiac miocyte activity.