Microfluidic Electrochemical Impedance Sensor for Hematological Tests of Blood under Different Osmotic Conditions

Blood tests are widely used to assess a patient's health status. Microfluidics, in combination with electrochemical impedance spectroscopy (MEIS), opens up great prospects for blood analysis. This study aimed to improve the MEIS blood tests. The shape and corpuscular volume of erythrocytes are vital to health care. Erythrocytes change their shape and dielectric properties under different osmolality conditions. Phosphate-buffered saline (PBS) was used to prepare an isotonic solution. Adding salt to PBS induces a hypertonic state. Dilution of PBS with water led to a hypotonic state. Several samples of blood suspensions were prepared with different tonicities. Optical and holotomographic microscopy were used to obtain images of erythrocytes in solutions with different tonicities. The blood impedance was measured by using a two-electrode system. A theoretical approach based on effective medium theory was adopted to analyze the impedance spectrum. The preferred orientation of erythrocytes in the microchannel and hemoglobin hydration were taken into account. The dielectric properties of the plasma, membrane, and cytoplasm of erythrocytes were determined, and the change in the erythrocyte shape was assessed. The proposed method was applied for partial blood count, which includes erythrocyte count (RBC), hemoglobin level (Hb), hematocrit (HCT), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC). The accuracy of the blood count was confirmed by routine hematological analysis. Additionally, the viscosity of plasma and erythrocyte intracellular fluid was estimated. These results provide a new method of blood testing and could become a valuable tool for point-of-care diagnostics.