NONLINEAR DIELECTRIC SPECTROSCOPY OF BIOLOGICAL SYSTEMS: PRINCIPLES AND APPLICATIONS

摘要

Biological cells can be seen, electrically, as consisting of conducting internal and external media separated by a more-or-less non-conducting cell membrane. The classical, linear, p-dielectric dispersion results from the charging up of this nominally 'static' membrane capacitance according to a Maxwell-Wagner type of mechanism, and typically occurs in the radiofrequency range. However, because practically all of the external macroscopic field is dropped across the 5 nm thick cell membrane, there is an effective and substantial amplification of the field across this membrane. This is predicted, and is found, to produce substantial nonlinearities when attempts are made to measure harmonics of the single-frequency exciting field. The nature (odd vs even) and magnitude of these harmonics changes substantially with cell status and environment, providing opportunities for using the cells themselves as sensing elements to describe their surroundings. Electrode polarisation effects producing nonlinear dielectricity can confound these measurements and must be bypassed or taken into account Nonlinear dielectric spectroscopy (NLDS) provides a wholly non-invasive approach to cellular characterisation and diagnosis.