Impedance measurements provide basic electrical properties and are used to analyze the characteristics of electrochemical materials for biomedical applications. The extracellular fluid (ECF) in microfluidic devices greatly affects the accuracy of impedance measurements of cells. When a single cell is placed in large amounts of ECF, the electric current mostly passes through the ECF, not the cell. Hence, this work presents a modeling method that is demonstrated in numerical and analytical solutions for eliminating the effect of ECF in coplanar impedance sensors. The proposed modeling method uses fundamental formulas of circuits that include the electrical parameters of the ECF, cytoplasm, and cell membrane. Equivalent circuit models for the coplanar impedance sensor are established to simulate the impedance as well as the measured ones for excitation frequencies in the range of 11-101kHz. According to the calculation result using the proposed modeling method, the cytoplasm resistance, membrane capacitance, medium resistance, and medium capacitance of HeLa (human cervix adenocarcinoma) cell are 13.5k, 122.6pF, 27.9k, and 337.7pF, respectively. Moreover, the electric current distribution in the coplanar impedance sensor is investigated using finite element method (FEM) simulation software. The variation in the impedance during measurements with the simultaneous application of an alternating-current (AC) voltage amplitude of 0.4V(pp) in the fluid volume range of 9-144 mu L is also studied.
