| Summary: | 博士 === 國立成功大學 === 電機工程學系 === 102 === Impedance measurements provide basic electrical properties and are used to analyze the characteristics of electrochemical materials for biomedical applications. In the present study, the battery-powered portable instrument system for single-cell trapping and analyses is developed. A method of alternating-current electrothermal (ACET) and dielectrophoresis (DEP) are employed for the cell trapping and the method of impedance spectroscopy is employed for cell characterizations. The proposed instrument (160 mm × 170 mm × 110 mm, 1269 g) equips with a highly efficient energy-saving design that promises approx. 120 hours of use. It includes an impedance analyzer performing an excitation voltage range at a voltage range of 0.2-2 Vpp and a frequency sweep of 11-101 kHz, a function generator with the sine wave output at an operating voltage of 1-50 Vpp and a frequency of 4-12 MHz, a cell-trapping biochip, a microscope, and an input/output interface. The biochip for the single cell trapping is designed and simulated based on a finite element method (FEM). In order to improve measurement accuracy, the curve fitting method is adopted to calibrate the proposed impedance spectroscopy. The measurement results from the proposed system are compared with the results from a precision impedance analyzer. Moreover, an analytical modeling method is used to calculate the cytoplasmic resistance, cell membrane capacitance, medium resistance and medium capacitance. Many advantages are offered in the proposed integrated instrument system such as the small volume, real-time monitoring, rapid analysis, low cost, low-power consumption and portable application.
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 the modeling method for eliminating the effect of ECF in coplanar impedance sensors. The method is demonstrated using numerical and analytical solutions. 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 11-101 kHz. For a single HeLa (human cervical epithelioid carcinoma) cell, the impedance magnitude decreases from 17.91 to 4.03 kΩ and the impedance phase increases from -72.28º to -59.04º at 0.4 Vpp in 11-101 kHz. According to the calculation result using the proposed modeling method, the cytoplasmic resistance, membrane capacitance, medium resistance, and medium capacitance of HeLa cell are 9.3 kΩ, 180.6 pF, 23.7 kΩ, and 265.6 pF, respectively. Moreover, the electric current distribution in the coplanar impedance sensor is investigated using FEM simulation software. The variation in the impedance during measurements with the simultaneous application of an alternating-current (AC) voltage amplitude of 0.4 Vpp in the fluid volume range of 9-144 μL is also studied. Many advantages such as the portable application in remote areas, the small volume, the real-time monitoring, the rapid analysis, the low cost and the low power consumption are offered in the integrated system.
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