鎘離子( Cd (II)）為劇毒的重金屬污染物，它不但具有長生物半衰期和強蓄積性，即使在低劑量攝入下也可能對健康造成不可逆的危害。常見的重金屬檢測方式如光譜法及質譜法。但這些技術成本高、耗時長且操作繁複，因此無法達到及時精準檢測的需求。
在此研究中，我們提出了一種基於適配體的電雙層 (EDL) 延伸閘極場效電晶體感測器檢測鎘離子（Cd (II)），適配體藉由Au-S鍵自組裝在金電極表面。由於適配體對鎘離子有特異性結合，添加 Cd (II) 後，結合適配體形成一莖環結構，而產生的閘極電壓變化，再透過場效電晶體的跨導 (transconductance) 來放大電訊號。此感測器對Cd (II) 的線性檢測範圍為10 pM-10 uM（R2=0.99001）以及提供出色的檢測極限為0.325 pM (LOD)。為了增強電信號，研究了溫度對結構變化的影響，透過加熱誘導，使它實現了 10 秒的快速響應。 此外，該感測器在存在其他重金屬時表現出高選擇性。除此之外，它還可以重複使用，而不會出現顯著的信號衰減。
目前，由於檢測真實樣本中的酸鹼值、溶液導電度、高離子濃度導致的屏蔽效應等因素，將對測量結果產生影響，進而增加了測量真實樣本的挑戰。因此，我們提出了一種替代高離子強度溶液，具有較低的電荷屏蔽效應，以提供超出德拜長度的範圍內有更好的檢測方式。牛血清蛋白 (BSA) 可用於增強溶液導電度和避免屏蔽效應導致的訊號減弱。此方法攜帶方便、響應時間短、操作簡單、靈敏度高、等優點。此感測器可直接在真實樣品中成功檢測鎘離子濃度，並且與 ICP-MS的結果類似。

Cadmium ions (Cd (II)) are highly toxic heavy metal pollutants that have a prolonged biological half-life and exhibit bioaccumulation. Even at low doses, irreversible damage to health may occur. Common methods of heavy metal detection include spectrometry and mass spectrometry. Nevertheless, these methods are very costly, time-consuming, and complicated. Thus, they are unable to meet the demand for timely and accurate testing.
In this research, we aim to develop an aptamer-based extended-gate field-effect transistor (FET) sensor to detect cadmium ions. The aptamer is self-assembled on a gold electrode with an Au-S bond. Due to the specific affinity of the aptamer for cadmium ions, it will form a stem-ring structure upon binding with Cd (II). The change in structure produces a change in Vg, which consequently amplifies the signal via the transconductance of the FETs.
The sensor shows a linear range of 10 pM to 10 μM (R2 = 0.99001) and provides excellent detection limits of 0.325 pM (LOD). In order to enhance the electrical signal, temperature was investigated, and heat induction achieved a rapid response of 10 seconds. In addition, it shows high selectivity even in the interference of other heavy metals also can be reusable, and has no significant signal degradation.
So far, real sample detection has posed challenges such as pH values, solution conductivity, and screening effects. Therefore, we propose an alternative high ion strength solution with low charge screening to provide better detection beyond the Debye length. Bovine serum albumin (BSA) can be used to enhance solution conductivity and avoid signal attenuation due to screening effects. This method has convenient portability, short detection time, high sensitivity, and simple operation. It successfully detected cadmium ion concentrations directly in real samples, and the results were similar to those of ICP-MS.

摘要 i
Abstract ii
致謝 iii
Table of contents iv
List of figures vi
List of Tables x
Chapter 1 Introduction 1
1.1 Motivation 1
1.2 Project Goal 2
Chapter 2 Literature Review 4
2.1 The danger of cadmium ions to the human health 4
2.2 Different Aptamer-based Sensor Methods for Cadmium Ion Detection 5
2.3 Field effect transistor biomedical sensor 14
2.4 Aptamers as Biological Receptors 15
2.5 Mechanism of aptamer binding to cadmium ions 16
2.6 Electric Double Layer Structure (EDL) and Charge Screening Effect 19
Chapter 3 Experimental Design and Preparation 23
3.1 Experimental method 23
3.1.1 Experimental device 24
3.1.2 Continuous addition method 26
3.2 Structure of Extended Gate FET 27
3.3 Application of electric double layer (EDL) 31
3.4 Selection of cadmium aptamer sequences 33
3.5 Preparation of test solution 35
3.6 Aptamer-modified electrodes 36
3.6.1 Surface Cleaning and Modification 36
3.6.2 TCEP 37
3.6.3 Aptamer immobilization 37
3.6.4 Cadmium ion elution process 38
3.7 Electrical Signal Measurement 39
3.8 Fluorescence measurement 40
Chapter 4 Results and Discussion 42
4.1 Electrical characteristics of Metal Oxide Semiconductor Field Effect Transistor 42
4.2 Chip Testing. 45
4.3 The challenge of real-sample detection 46
4.3.1 The effect of solution conductivity 46
4.3.2 Effect of pH 48
4.3.3 Effect of temperature 49
4.3.4 Optimization of adaptor immobilization conditions 58
4.4 Sensitivity 59
4.5 Blind test 65
4.6 Selectivity 66
4.7 Repeatability 70
4.8 Chip Storage 70
4.9 Detection results of real samples 72
4.9.1 Sample preparation 72
4.9.2 A new method to overcome the screening effect 76
4.9.3 Detection method 81
4.9.4 Results of testing real samples 82
Chapter 5 Summary 85
Chapter 6 Future Work 87
Chapter 7 Reference 88

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