A Nanoscale Galvani Experiment

A nanoscale galvani experiment provides a new way to obtain images of biological tissue. Applying state-of-the-art technology to a seldom-exploited electromechanical property in biomolecules, Sergei Kalinin of Oak Ridge National Laboratory (sv9@ornl.gov) and his colleagues have demonstrated a nanometer-scale version of Galvani's experiment, in which 18th-century Italian physician Luigi Galvani caused a frog's muscle to contract when he touched it with an electrically charged metal scalpel. Described at this week's AVS Science & Technology meeting in Boston, the new, 21st-century demonstration promises to yield a host of previously unknown information in a variety of biological structures including cartilage, teeth, and even butterfly wings.

Employing a technique named Piezoresponse Force Microscopy (PFM), Kalinin and colleagues sent an electrical voltage through a tiny, nanometer-sized tip to induce mechanical motion along various points in a biological sample, such as a single fibril of the protein collagen. The electromechanical response at various points of the sample, as measured by the probe tip, enabled the researchers to build up images of the collagen fibrils, with details less than 10 nanometers in size. This resolution surpasses the level of detail that can be gleaned on those biostructures by ordinary scanning-probe and electron microscopes (get a lengthier description here).

The PFM technique exploits the well-known but infrequently used fact that many biomolecules, especially those that are made of groups of proteins, are piezoelectric, or undergo mechanical deformations in the presence of an external electric field. The researchers have used the PFM technique to produce images of cartilage as well as enamel and dentin (found inside teeth). Besides providing images of biostructures on a nanometer scale, the new technique yields information about the electromechanical properties and molecular orientation of biological tissue. In recent work, the researchers even found unexpected piezoelectric properties in butterfly wings which enabled them to yield molecular-level images of wing structures.

Kalinin, et al., meeting paper NS-WeM3 and lay language paper