| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 99 === Electrochemical impedance spectroscopy (EIS) has been widely used in many applications such as biosensors over these decades. For the development of electrochemical sensor, the condition and property of electrode surface play a crucial role. The factors of how the surface property affects the electrochemical response have been studied for years; however, a more detailed research of the mechanism is still required. In a faradaic EIS, a Randles model is often used to fit the measured impedance data and the circuit element of charge transfer resistance (Rct) dedicates the most of the impedance change. Apart from the energy potential of the redox pair, steric hindrance and electrostatic force are the two well-known factors responsible for the Rct change. To further investigate how these two factors affect the Rct element, we used conductive atomic force microscopy (CAFM), zeta potential measurements and electrochemical method as tools. In this study, 7 kinds of conductive linkers and a conventional alkanethiol linker were used to form the self-assembled monolayers (SAMs) on the gold electrode. From the experimental results, it can be found that the Rct increases logarithmically with monolayer resistance, and decreases exponentially with the surface charge. This result indicates that the steric hindrance plays a minor role in the Rct change when compared to that of the electrostatic force.
By this understanding, we can design a low impedance linker to enhance the signal-to-noise ratio. This enhanced signal can also improve the sensor sensitivity and detection limit. Here we found a linker ATP, which possess a good conductive property and ends with a positive charged functional group. By using ATP, we enhanced the measured signal and improved the sensor sensitivity. Therefore, we can use a simplified electronic circuit to make the biomolecule detection. This study is useful for the point-of-care testing implementation of impedance based biosensor.
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