Electrochemical impedance spectroscopy of blood for sensitive detection of blood hematocrit, sedimentation and dielectric properties

Abstract

Electrochemical impedance spectroscopy (EIS) is a highly promising tool for the analysis of blood. The electrical properties of plasma and blood cells provide fundamental insights into the health status of patients. Nevertheless, the potential of EIS has not been fully exploited to date. In this study, a small chamber with two planar electrodes placed at the bottom is used for sensitive detection of blood hematocrit, sedimentation and dielectric properties of plasma and erythrocytes. The changes in the blood impedance spectrum were measured at frequencies between 40 Hz and 110 MHz for a few hours. An updated lumped-parameter circuit is proposed to describe the impedance in the measuring chamber filled with blood. This updated circuit model allows the correction of the polarization effect and exclusion of the stray capacitance from experimental data with a high accuracy. A theoretical approach based on the effective medium theory is developed for calculating the effective permittivity and conductivity of whole blood. An algorithm is proposed to extract the electrical properties of erythrocyte cytoplasm and membranes from the impedance spectrum. The EIS of blood samples reveals β- and δ-dispersions. It is found that the electrical properties of membranes have a significant influence on the blood impedance at frequencies between 100 kHz and 10 MHz (β-dispersion), while the cytoplasm has an effect at frequencies between 10 MHz and 1 GHz (δ-dispersion). The proposed method provides an estimation of hematocrit levels during blood sedimentation, which is important for blood tests.