Microwave Techniques in Biophysical Measurements*

Abstract

One of the emerging fields of study in biophysics and bioelectronics is the investigation of the role of water in living systems. Microwave frequencies are well suited for studies of water since “free” water shows a Debye dispersion with a relaxation time of 10^-10 sec. Differential volumetric techniques were devised to allow measurements of changes in the water structure surrounding active macromolecules such as enzymes. Another microwave technique—-Faraday rotation—was adapted to measure the concentration of free dipoles in systems consisting of macromolecules and varying amounts of water. Since some enzymes (e.g., urease) can act as catalysts even in a relatively dry environment, a combination of the above two techniques allows one to clarify structural changes in the water surrounding enzymes while they are interacting with their substrate molecules. The Faraday rotation technique is also used as a contactless Hall-effect measurement to study the mobilities ofcharge carriers in organic semiconductors which are of importance in biological systems. Several “non-thermal” effects of microwaves have been reported in the literature but as yet have eluded precise substantiation and interpretation by molecular events. A new model is proposed based on the frequency variation of the dielectric constant of bound andfree water and the thermal characteristics of the cellular and interstitial system. The model postulates microthermal effects which produce temperature gradients that result in thermoosmotic and thermoelectric aftereffects.