Microvolume Dielectric Spectroscopy and Molecular Dynamics of Amino Acids

Abstract

Accurate knowledge of electromagnetic properties of biosystems is essential for the novel physical methods for therapy and diagnostics in medicine and biotechnology.To study the dynamics and electrical properties of biomolecules, we have designed, fabricated, and tested novel grounded coplanar waveguide-based chip for dielectric spectroscopy of liquid samples in 0.5 - 40 GHz band made on RO4350B substrate and we implemented a method for the permittivity extraction based purely on the extraction from measured scattering parameters.To our knowledge, the proposed bio sensing method represents an advantage over the current known sensing chips because the dielectric function of sample is obtained purely by using precision calibration techniques (NIST multi-line TRL) and computational optimization (CST Microwave Studio) without any a priori assumption about the dielectric model of measured sample. This chip is designed with well-defined active area to achieve the high sensitivity to dielectric change, enables perfect repeatability of sample position without the need of any microfluidics. Furthermore, due to its sensing size, the chip permits to work with only 250 microliter sample volume.In the pioneering experiments, we focused on dielectric (i.e. polarization) properties of solutions of amino acids, as building blocks of proteins. Alanine has been selected. The polar nature of amino acids determines their behavior in aqueous solutions and due to fact that at least one relaxation process is anticipated in microwave band, it allows us to study their dynamics and structure which employ using broadband dielectric spectroscopy. Data extracted from experiment are in an exact agreement in comparison with widely used commercial reflection method by coaxial probe (85070E Dielectric Probe Kit). Data show the trend of rising static permittivity at low frequencies with rising concentration of amino acids and also show the shift of relaxation times. We also performed molecular dynamics simulations to predict the complex permittivity of amino acid solution and obtained good agreement with experimental data. The presented procedure enables simple experimental verification of molecular dynamics of biomolecules by the dielectric spectroscopy using our microvolume chip.We acknowledge support by the Czech Science Foundation, project no. P102/15-17102S. Authors participate in COST Action BM1309 and bilateral exchange project between Czech and Slovak Academies of Sciences, no. SAV-15-22.