Effect of hemoglobin hydration on the physical properties of erythrocyte cytoplasm and whole blood

Electrochemical impedance spectroscopy of whole blood and blood cells has great potential for assessing the health of patients. This potential has not been fully exploited for a detailed examination of the erythrocyte interior. The erythrocyte interior (cytoplasm) is often considered as continuous media. However, cytoplasm is a colloidal suspension of hydrated hemoglobin molecules. This study mainly focuses on the effect of hemoglobin hydration on the dielectric properties of erythrocyte cytoplasm and whole blood. The impedance spectra of separated cytoplasm and whole blood were measured at frequencies from 1 kHz to 110 MHz. The effective medium theory was used to analyze the experimental data. The cytoplasm was found to be best described as a colloid of hemoglobin cores surrounded by double hydration shells. The dielectric properties of the hemoglobin core, hydration shells and free intracellular fluid, as well as the thickness of the shells, were numerically determined from the impedance spectrum. An approach was developed to determine the intracellular fluid's viscosity and the density of bound water in the hydration shells. It shows that the hemoglobin hydration has a significant effect on the physical properties of blood. The detailed electrical properties of the cytoplasm can be detected from the impedance spectrum of whole blood.