  Electromechanical coupling is ubiquitous in biological systems with examples
ranging from simple piezoelectricity in calcified and connective tissues to
voltage-gated ion channels, energy storage in mitochondria, and
electromechanical activity in cardiac myocytes and outer hair cell stereocilia.
Piezoresponse force microscopy (PFM) has originally emerged as a technique to
study electromechanical phenomena in ferroelectric materials, and in recent
years, has been employed to study a broad range of non-ferroelectric polar
materials, including piezoelectric biomaterials. At the same time, the
technique has been extended from ambient to liquid imaging on model
ferroelectric systems. Here, we present results on local electromechanical
probing of several model cellular and biomolecular systems, including insulin
and lysozyme amyloid fibrils, breast adenocarcinoma cells, and
bacteriorhodopsin in a liquid environment. The specific features of SPM
operation in liquid are delineated and bottlenecks on the route towards
nanometer-resolution electromechanical imaging of biological systems are
identified.
