Single cells analysis using impedance measurement and FEM simulation
| Autor: | Min-HawWang, 王明浩 |
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| Rok vydání: | 2010 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 98 The electrical properties of single cells provide fundamental insights into their pathological condition and are therefore of immense interest to medical practitioners. Accordingly, this thesis captures single HeLa cells using a microfluidic device and then measures their impedance properties using a commercial impedance spectroscopy system. The microfluidic device includes a glass substrate with metal electrodes and a PDMS (Poly-dimethylsiloxane) channel with micro pillars. The computation fluid dynamics software is used to study the flow of the microstructures in the channel. According to simulation results, the probability of cell capture by three micro pillars is about 10%. The experimental system is modeled by an equivalent electrical circuit and FEM (Finite element method) simulations are then performed to establish the conductivity, permittivity and impedance of single HeLa cells under various operational frequencies ranging from 1 to 100 kHz and voltages between 0.1 and 1.0V. The equivalent circuit model of the device is established and fits closely to the experimental results. At an operational voltage of 0.2 V, the maximum deviation between the experimental and simulation results for the magnitude and phase of the HeLa cell impedance is found to be 9.5% and 4.2%, respectively. The magnitude of the HeLa cell impedance declines at all operation voltages with frequency because the HeLa cell is capacitive. Additionally, increasing the operation voltage reduces the magnitude of the HeLa cell because a strong electric field may promote the exchange of ions between the cytoplasm and the isotonic solution. Below an operating voltage of 0.9 V, the system impedance response is characteristic of a parallel circuit at under 30 kHz and of a series circuit at between 30 and 100 kHz. The phase of the HeLa cell impedance is characteristic of a series circuit when the operation voltage exceeds 0.8 V because the cell impedance becomes significant. In general, both sets of results show that the conductivity and permittivity of single HeLa cells increase with an increasing operational voltage. Moreover, an increasing frequency is found to increase the conductivity of HeLa cells at all values of the operational voltage, but to reduce the permittivity for operational voltages in the range 0.6–1.0 V. Based upon the simulation and experimental results, empirical equations are constructed to predict the conductivity and permittivity of single HeLa cells under specified values of the operational voltage and frequency, respectively. The maximum discrepancy between the predicted results and the simulation results for the permittivity and conductivity of the HeLa cells at an operational voltage of 0.2V is found to be just 0.5% and 4.5%, respectively. Additionally, in order to facilitate the development of single cell analysis for disease diagnosis and detection in the medical, portable impedance analyzers is also presented in this thesis. The minimized impedance spectroscopy consists of a power supply chip (ADR423), an impedance measurement chip (AD5934) and a microcontroller chip (C8051F320). The functional chip is developed specially to provide a portable, low cost, easy to use, and it is performed to automatic collection of data. Moreover, the measurement accuracy and reliable obtained by the proposed system and a conventional precision impedance analyzer are verified. The measurement accuracy and reliability of the minimized impedance spectroscopy using single latex beads are about 97.10% and 96.34%, respectively. Finally, the proposed system is used to measure the magnitude of HeLa cells and MCF-7 cells. The results demonstrate that the proposed impedance sensing platform as well as the equivalent circuit model with frequency range successfully distinguishes the HeLa cells and MCF-7 cells at between 11 and 101 kHz. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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