Analysis of Complex Permittivity of Liposome for Its Biochemical Dynamics up to 30 GHz Range

We have successfully measured the complex permittivity of liposome as very important biochemical species, dependent on frequency up to 30 GHz (millimeter-wave range), for the first time, by an open-ended coaxial probe method improved for measuring a very small amount of liquid solution. We used a probe size as small as 1.2 mmphi, which leads to upper frequency limit usable of 90 GHz. Also found that the method is very suitable for evaluation of series of biochemical solution with a small amount (1-2 ml) in a short period. It is revealed, as a result of membrane dynamics of liposome, that 1) temperature dependency of relaxation time of DPPC liposome in dispersion regions (0.2-30 GHz), is attributed to bulk water, cation and anion, 2) increase in the relaxation time results from dynamics of trapping/bounding of water by cation and anion, and 3) cholesterol addition to liposome gives a new dispersion (around 1 GHz), possible to relate to water molecules that freely move in/on the liposome surface. We think the method is a promising tool for exploring basic biochemistry of liposome and related solution systems