本研究將辣根過氧化物酶 (HRP, horseradish peroxidase) 固定於導電聚合物薄膜，聚苯胺 (PANI, polyaniline)，以製造高靈敏過氧化氫感測器。感測器的反應機構，是透過溶液中的過氧化氫氧化HRP，氧化的HRP進而氧化PANI獲取電子，然後造成PANI薄膜的導電度下降。還原後的HRP可以繼續和過氧化氫作用，重複上述的氧化還原反應直到溶液中的過氧化氫全部作用完畢。而感測器的訊號，便是來自所有反應完成之後PANI薄膜的導電度變化。本感測器的偵測極限達 0.7 nM ，偵測濃度範圍為 0.7 nM 至 1 μM。由於高濃度過氧化氫會抑制HRP，當過氧化氫濃度超過 1 μM之後，感測器的訊號逐漸飽和，而待測溶液開始殘留未消耗的過氧化氫。另外，當感測器沒有固定HRP，對於待測溶液中的過氧化氫沒有反應，證明酵素反應在偵測中過程中的必要性。
本感測器擁有價格低廉、容易製作的優點，適合發展可攜式的一次性感測晶片；未來，利用其高靈敏度的特性，結合其他酵素更能發展其他種類的感測器。

In this study, we fabricate an ultra-sensitive hydrogen peroxide sensor by using horseradish peroxidase (HRP)-immobilized conducting polymer, polyaniline (PANI). With the proposed detection mechanism, hydrogen peroxide first oxidizes HRP, which then oxidizes polyaniline, thus resulting in decreased conductivity of the polyaniline thin film. The reduced HRP can be further oxidized by hydrogen peroxide and the cycle of the oxidation/reduction would continue until all hydrogen peroxide are reacted, leading to the high sensitivity of the sensor due to the signal contributed from all hydrogen peroxide molecule. The detection limit of this sensor is only 0.7 nM. The detectable concentration of H2O2 is from 0.7 nM to 1 μM. Beyond 1 μM, the sensor gradually saturates and some H2O2 remains, indicating the inhibition of HRP activity at high concentration of H2O2. There is no response to hydrogen peroxide once the PANI is standalone without HRP immobilized, showing the enzymatic reaction is required in the process of hydrogen peroxide detection. The simple process for the sensor fabrication allows the sensor to be cost-effective and disposable. This electronic hydrogen peroxide sensor is promising in applications for low concentration hydrogen peroxide detections, such as the reactive oxygen species (ROS) in oxidative stress studies.

CHAPTER 1 INTRODUCTION 1
1.1 Motivation 1
1.2 Backgrund 2
CHAPTER 2 LITERATURE REVIEW 3
2.1 HRP-immobilized PANI thin film H2O2 sensor 3
2.2 PANI Doping and N-Alkylated PANI 3
CHAPTER 3 EXPERIMENT METHOD 4
3.1 Preparation of PANI thin film on substrate 4
3.2 Sultonation and HRP-immobilization of polyaniline thin film 4
3.3 Sensor measurements 5
CHAPTER 4 RESULTS AND DISCUSSION 6
4.1 Overall sensing capability and range 6
4.2 Reuse of the sensor 9
4.3 Possible sensing mechanism of the sensor in detectable region and in detection limit 12
4.4 Saturation of the sensor at concentration of high hydrogen peroxide 14
4.5 Evaluation of the effects of other oxidants on the hydrogen peroxide sensors 14
CHAPTER 5 CONCLUSION 16
CHAPTER 6 APPLICATION 17
CHAPTER 7 REFERENCE 18
SUPPLEMENTARY MATERIAL 20

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