Nanostructured carbon-based materials for wearable sensors in human biophysical monitoring

Nanostructured carbon-based materials for wearable sensors in human biophysical monitoring

It is advantageous for individuals to self-monitor their vital biophysical signals, such as heart rate, respiratory rate, or body motions for better health management. These signals can be detected by wearable physical sensors, such as strain sensors, pressure sensors, and electrophysiological sensors, with requirements on desirable sensing performance (e.g., high sensitivity, selectivity, high signal-to-noise ratio) and wearing comfort (e.g., softness, breathability). The popular materials for these sensors are metals and silicon. However, the physical sensors based on those materials either exhibit low sensing performance or possess stiffness that is unfavourable for human skin compliance. This research aims to understand the sensing mechanisms of aligned carbon nanotubes (ACNTs) and cubic-silicon carbide (3C-SiC) membranes for the fabrication of biophysical sensors, such as electrophysiological sensors, strain sensors, and pressure sensors, that exhibit desirable sensing performance and wearing comfort, with the major focus on ACNTs. This study investigates the sensing properties of the ACNTs embedded in soft polymer substrates applied for high-performance and skin-compliant electrophysiological sensors. Additionally, the study investigates the sensing properties of ACNT structures incorporated into the patterned surface of breathable bandages under stretching deformation and explores the application of the breathable bandage-based ACNT strain sensors for detection of human joint motions. Furthermore, the study explores the interaction between ACNTs and 3C-SiC nanomembrane to develop sensitive self-powered pressure sensors, providing insight into the impact of the material structure and mechanical deformation on self-powered sensing properties of the ACNT/3C-SiC structure. The results indicate the promise of the ACNT structures as electrophysiological and strain sensors, exhibiting desirable sensor performance and wearing comfort. The results also demonstrate the potential combination between ACNTs and 3C-SiC nanomembrane for high-performance self-powered pressure sensors. Moreover, insight into the effect of material structures, substrates, and mechanical deformation on the electrical properties and sensing response of ACNTs and 3C-SiC nanomembrane provides understanding for further optimization and improvement of carbon-based biophysical sensors. This thesis follows a "thesis by publication" format, incorporating published and submitted journal papers in Chapters 2, 3, 4, and 5.

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