Conductimetric and impedimetric devices

Abstract

Abstract The idea that (changes in) the electrical conductivity or impedance of a biological (or other) system may be used to sense biological activity goes back to the previous century (1). Notwithstanding, and despite many spectacular successes which include the discovery of the molecular thickness of biological membranes and the voltagegated conductivity of nerve axons, the generalized impedimetric approach (‘impedance or admittance spectroscopy’) remains astonishingly underexploited. Thus, Campbell and Dwek’s eponymous and otherwise excellent book, Biological Spectroscopy (2), does not even mention the technique. In the belief that this widespread lacuna is due to a general lack of appreciation of the relevant theory and terminology, we begin this chapter by a consideration of exactly what it is that is measured in an impedimetric experiment, and introduce the multifarious terminologies that many workers have applied to essentially the same phenomena. Given a proper appreciation of this, the practical approaches actually used, together with their pitfalls, follow naturally.