  Studies of biochemical liquids require precise determination of their complex
permittivity. We developed a microwave characterization technique on the basis
of a high-quality whispering-gallery mode (WGM) sapphire resonator with a
microfluidic channel filled with the liquid under test. A novel approach allows
obtaining the complex permittivity of biochemical liquids of
sub-microliter/nanoliter volumes with high accuracy. The method is based on
special procedure of analysis of the interaction of electromagnetic field with
liquid in WGM microfluidic resonator and measurements of both the WGM resonance
frequency shift and the change of the inverse quality factor. The approach is
successfully applied to obtain the complex permittivity in the Ka band of
glucose, albumin bovine serum, lactalbumin and cytochrome C aqueous solutions
using the developed microwave technique.
