|Title:||Organic electrochemical transistors for wearable sensing|
|Advisors:||Yan, Feng (AP)|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
|Department:||Department of Applied Physics|
|Pages:||xvi, 113 pages : color illustrations|
|Abstract:||Wearable biosensing technologies could serve as a useful tool for personalized healthcare management and have a massive market in the future. However, conventional electrochemical sensors have rarely been used in wearable applications due to relatively high detection limit and low sensitivity. Organic electrochemical transistors (OECTs) have emerged as a versatile sensing platform for different wearable applications due to its intrinsic amplification function and ion-to-electron transducing ability. In this thesis, the fabrication of a highly sensitive OECT sensor on a flexible fiber is firstly presented. The fiber-based sensor can provide in situ amplification of detection signal with high sensitivity. It shows very stable performance during bending tests, which is critical to applying this device into wearable electronics. The detection limit of the functionalized sensor to the target analyte can be down to 10 nM. The sensor response to the specific analyte is about two orders magnitude higher than that to other interferences, indicating the device's good selectivity. The fiber-based sensor is then woven together with cotton yarns, resulting in a flexible and stretchable fabric device. The fabric device can be integrated into a diaper and remotely operated by using a mobile device with a custom-made app. The fabric device integrated into a diaper is suitable for wearable biosensing because of its light-weight and compactness. Due to the advantages of wearability and high sensitivity, the fabric sensor can offer a unique platform for convenient wearable healthcare monitoring.|
Secondly, a quick response OECT senor is thoroughly investigated. The channel dimension of the OECT is finely tuned to realize quick stabilization of the channel current. The dual gate design of the sensor can eliminate certain interfering species (such as uric acid, ascorbic acid) in body fluids from detection of target analytes. After gate modification, numerous elements in body fluid can be quickly and selectively detected by the sensor. In order to efficiently perform wearable sweat sensing, a sweat absorption layer is assembled onto the sensor, resulting in a quick sampling of body fluids. The device conformably worn on a fingertip can quickly collect enough sweat in several minutes and perform sweat glucose test. The glucose level in sweat can be wirelessly monitored by a portable meter via a mobile phone, which can provide a non-invasive way for quick detection of various physiological signals of human body. Lastly, a flexible OECT device is fabricated and used for wearable electrocardiogram (ECG) recording. In order to increase the device response speed, the channel length of the device is decreased to about 2 m. The response time can be as short as tens of microseconds, which is sufficient for ECG signal recording. The channel and gate of the OECT can be mounted on different parts of human body to record ECG signal. By optimizing the distance between the channel and gate of the device, high-quality recording of ECG signal is achieved. The wearable monitoring of ECG signal is further demonstrated. The proposed ECG recording device can be integrated into the wearable electronic system for monitoring multiple clinical signals. In summary, fabric OECT sensors have been successfully fabricated and used for sensitive and selective detections of target analytes. Wearable and quick detections can be realized by using a dual gate OECT, and its operation mechanism is comprehensively investigated. The short-channel OECT with fast response speed is fabricated and used for ECG recording. By combing the merits of the above sensing techniques, the wearable OECT sensors could revolutionize the current wearable technologies in diagnostics and physiological monitoring.
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