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標題: | 對稱電極與指叉狀晶片電化學阻抗模型建立與適體感測應用 Electrochemical Impedance Modeling of Symmetric Electrodes and Interdigitated Array Chips for Aptasensing Applications |
作者: | Chih-Yu Lai 賴知佑 |
指導教授: | 陳林祈(Lin-Chi Chen) |
關鍵字: | 指叉狀電極,電化學阻抗頻譜,有限擴散,對稱電極,適體感測, interdigitated array (IDA) electrodes,electrochemical impedance spectroscopy (EIS),finite diffusion,symmetric electrodes,aptasensing, |
出版年 : | 2019 |
學位: | 碩士 |
摘要: | 腫瘤標誌之偵測與抑制成為近年癌症預防及治療的新趨勢,此類標誌常利用操作簡易及低成本之電化學阻抗頻譜法(electrochemical impedance spectroscopy,簡稱EIS)、配合靈敏度及專一性高的適體感測(aptasensing)技術進行量測,於近年之生物分析應用蓬勃發展。然而三極式電化學系統之微小化面臨設計與製程複雜、高成本與低製作良率等問題,且近年廣泛應用於電化學感測技術之二極式指叉狀電極(interdigitated array electrodes,簡稱IDA electrodes)因幾何特性複雜,尚未有根據其帶寬(bandwidth)與間距(gap width)推導其擴散阻抗(diffusion impedance)之文獻。因此本論文以對稱二極式阻抗感測模型之建立為主軸,推導不同幾何之指叉狀電極擴散阻抗公式,發展對稱二極式電極等效電路模型並進行阻抗式適體感測,主要以兩個部分進行探討並分述如下:第一部分著重於指叉狀電極擴散阻抗的理論推導與驗證。利用共形變換(conformal mapping)及圓柱有限長度近似方法(cylindrical finite length approximation)推導不同幾何之指叉狀電極擴散阻抗積分型公式解,並且套用在現今之指叉狀電極電化學系統中。此部分之研究導出能夠針對不同電極帶寬、間距、擴散係數…等參數而直接計算出其擴散阻抗之理論公式,九種不同帶寬與間距之指叉狀電極利用微製程技術製作而成。時間相依(time-dependent)二維擴散之模擬結果證實理論中假想等濃度邊界的存在與理論之可行性,理論所計算之0Hz擴散阻抗與前人研究所推導之極限電流計算公式的倒數有高度線性相關(R2 = 0.992),實驗所得極限電流倒數與計算之0Hz擴散阻抗具高度相關性(R2 = 0.970),所推導的公式能夠精準預測其電化學阻抗頻譜量測結果(R2 ≥ 0.948),且已驗證可透過此理論進行等效電路匹配(equivalent circuit fitting)並成功預測其電極幾何。此部分可提供指叉狀電極於低頻量測區間阻抗變化之解釋,有助於相關領域之學者對於此種系統的擴散行為更進一步的認知與等效電路模型之建立。第二部分推導對稱二極式電極等效電路模型並利用標準金電極(standard Au electrode,簡稱SGE)及指叉狀電極驗證模型可行性與應用於凝血酶(thrombin)及腫瘤標誌MUC1之量測。若利用單一Randles電路進行對稱電極系統之等效電路匹配,則其參數Rct與Rs會是實際值的兩倍、Q0與Y0會是實際值的一半、且n會與實際值相同。此理論利用兩種不同幾何之對稱電極晶片進行驗證,應用於適體感測器之初步概念驗證利用凝血酶(thrombin)作為感測標的且KD為129.4nM。MUC1與其硫醇基修飾過之DNA適體(5’SH-(CH2)6-S2.2)透過三極式適體感測器量測之KD為15.11nM,根據專一性結合模型計算之最大阻抗變化(Bmax)為7.91kΩ,接著發現MUC1之對稱二極式適體感測器量測之KD為15.92nM且Bmax為17.08kΩ,此兩組KD結果相近,而Bmax約為兩倍關係,與推導的模型所得到的結果一致,證明此理論模型應用於生物感測的正確性。利用指叉狀電極製作的凝血酶適體感測器,其電化學阻抗頻譜結果可利用第一部分根據理論所製作的等效電路匹配程式得到準確的參數,且此感測器具有可重複測量六次之再生性(regenerability)以及專一性(specificity)。對稱二極式金電極系統簡單、低成本與適體之高度穩定性極有助於商業化過程之大量生產與客製化。藉由上述之研究成果,期望在未來可利用指叉狀電極進行微小化發展並應用於相關醫療診斷,更甚能實現於個人化醫療與定點照護中。 The inhibition of tumor markers has been a popular research object among the academic society. They are often detected using simple and low-cost techniques such as electrochemical impedance spectroscopy (EIS), which aptamers are occasionally used as the sensing element for achieving high sensitivity and selectivity. This integrated method has flourished in recent years. However, for electrochemical methods, a three electrode setup faces fabrication complexity, high cost and low yield rates during miniaturization. Two electrode impedimetric detection using interdigitated array (IDA) electrodes also faces a problem. Due to its geometry, there hasn’t been any studies that derive its diffusion impedance according to different bandwidths and gap widths. Therefore, this study makes a basis on impedimetric modeling of symmetric two electrode systems. The first part focuses on the derivation and verification of an integral form of solution for IDA diffusion impedance. Conformal mapping and cylindrical finite length approximation methods are used in theory. Simulations are performed for confirming assumptions such as the imaginary constant concentration boundary (ICCB). Nine electrodes of different bandwidths and gap widths are fabricated with their heights and symmetric electrochemical characteristics verified. The calculated zero-frequency impedance showed high correlation with the reciprocal of limiting current calculated from previous studies (R2 = 0.992) and from chronoamperometry experiments (R2 = 0.970). Further evidence for the correctness of theory is established due to the fact that experimental EIS data and calculated impedances are highly consistent (R2 ≥ 0.948 for real and imaginary part). This sheds some light on explaining the phenomenon of diffusion impedance using IDA electrodes in the low frequency spectrum. An equivalent circuit fitting program succeeded to accurately fit the EIS data and parameters such as the ratio of electrode bandwidth to gap width and diffusion coefficient can also be obtained by fitting the data from a single EIS experiment. This can aid researchers in relevant fields model their systems more accurately. In the second part, a symmetric equivalent circuit model is developed, and it is applied it for impedimetric detection of thrombin and a tumor marker MUC1 with a fabricated aptasensor using standard Au electrodes (SGE) and IDA chips. If a single Randles circuit is used for equivalent circuit fitting on a symmetric electrode system, Rct and Rs would be double the real value, Q0 and Y0 would be half the real value, and n would be the same. This relationship is proven using experimental data from two kinds of micro-fabricated symmetric electrode chips. Thrombin is used for the proof of concept and a KD of 129.4nM is obtained using the symmetric electrode setup. MUC1 is detected by the thiolated S2.2 aptamer using a three electrode setup and the KD is 15.11nM. The calculated max binding value (Bmax) according to one-site specific binding model is 7.91kΩ. Using a two electrode setup, the KD is 15.92nM and the Bmax is 17.08kΩ. The calculated KD values for two and three electrode setups are consistent, and the ratio between Bmax is about 2, which corresponds to the developed model. This proves the correctness of the model applied for bio-detection. IDA chips are used for aptasensor fabrication for thrombin detection. The program designed in the first part is used for circuit fitting of EIS data, and accurate parameters are obtained. This sensor has the regenerability for six times of detection and the specificity is also confirmed. Symmetric Au electrode systems have simple and low fabrication cost characteristics. Its integration with highly stable aptamers can contribute to mass production and customization in product commercialization. According to the above results, the author anticipates future developments in relevant medical diagnosis and point-of-care applications. |
URI: | http://tdr.lib.ntu.edu.tw/handle/123456789/742 |
DOI: | 10.6342/NTU201901821 |
全文授權: | 同意授權(全球公開) |
顯示於系所單位: | 生物機電工程學系 |
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