UC San Diego

The development of resistive-based strain sensors comprising nanomaterials has become of interest for the past decade. Some of the interest in these types of sensors are due to their notable sensitivity, enabled by sensing mechanisms stemming from size confinement not seen in the bulk form of these materials. Apart from their sensitivity, these nanomaterials capable of detecting mechanical strain are also capable of being transferred to various hard, flexible and stretchable substrates. The ability to be used in compliant substrates overcomes the limitations seen in MEMS strain sensors, which can expand the array of their potential utility to applications such as wearable sensors. By developing an ultra-sensitive nanomaterial capable of detecting a wide strain range, it is possible to develop devices capable of monitoring human mechanical strain activity (from the cellular level to human motion). The ability to detect mechanical activity of biological phenomenon can be relevant in the medical field by developing deployable devices capable of giving clinicians reliable and actionable data. This thesis investigates the performance of a material comprising a subcontiguous film of noble metal supported by single-layer graphene (referred throughout as nanoislands, or Gr/M where M is the metal used), when used in devices for the detection of biomechanical deformations originating from human physiological activity. Chapter 1 introduces the Gr/M material and gives an overview of the various sensing modalities Gr/M possesses, while discussing recently developed sensing devices using this material. Chapter 2 and Appendix B present an iteration of a device, comprising Gr/Pd on a flexible substrate, for use as a wearable device to monitor swallowing activity in head and neck cancer patients. This study involves a 14-patient cohort study of head and neck cancer patients after radiation or surgery and the development of a machine learning algorithm to analyze the data given by the wearable strain sensor. Chapter 3 and Appendix C incorporates a layer of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) on top of the Gr/Pd film, which increases the dynamic range of strain detectable by the composite film while retaining its sensitivity. Chapter 4 and Appendix D presents an empirical study comparing the material properties of Gr/M and composites comprising subcontiguous metal films on hexagonal boron nitride (hBN). The goal of this study is to help elucidate the possible sensing mechanism(s) responsible for the material’s sensitivity to strains as low as 0.0001% (1 ppm) strain.