Microwave characterization of aqueous amino acid solutions using the multifrequency WGM resonator technique.

Amino acids play essential role for humans. We studied the dielectric properties of the basic aliphatic amino acids and polar positive amino acids in solutions of different concentrations. The high-Q single microwave whispering gallery-mode (WGM) quartz dielectric resonator based technique, enhanced to a number of measurement frequencies, was applied. The technique allows liquid investigation of micro- to nano- liter volumes filled in microfluidic channel on six discrete frequencies in the 30-40 GHz range. The dependencies of the complex permittivity on the molar mass show almost linear behavior for aliphatic amino acids at different concentrations. The study results are in good agreement with the calculated data obtained by Cole-Cole equation.

Microwave characterization of low-molecular-weight antioxidant specific biomarkers.

Antioxidants play a crucial role in the life sciences, as the regulators of biochemical reactions. We studied the dielectric properties of the low-molecular weight antioxidant specific biomarkers sodium ascorbate and glutathione in solutions of different concentrations. The biomarkers are multifunctional metabolites relevant to the reactive oxygen species (ROS) scavenging system of cells. The newly developed high-Q microwave whispering-gallery-mode (WGM) dielectric resonator based technique was applied. The technique allows investigation of liquids of nanoliter volumes filled in microfluidic channel within several milliseconds. The revealed peculiarities in the dependence of permittivity on concentrations of the sodium ascorbate and glutathione solutions are explained by differences in relaxation times and loses introduced by molecules of different shapes. We suggest that this novel approach offers the potential for the detection and characterization of ROS-relevant biomarkers with millisecond-time resolution.