TMDC-based Soft and Wearable Bioelectronics Toward Precision Health Care Open Access
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Driven by the tremendous increasing demand for timely and continuous health monitoring and recording, precision health care devices on the body and in the home are gaining attraction for both researchers and the market. Epidermal and wearable sensor systems with the ability to monitor the physiological signals and the surrounding environment are gathering significant interest due to their formidable potential for practical applications in health monitoring. New sensing nanomaterials, such as quantum dots, nanotube, nanowire, graphene and two-dimensional transition metal dichalcogenide (TMDC) are recently offering candidates that allow room temperature sensing with high sensitivity, high selectivity and fast response. Among them, TMDC is now attracting substantial attention owing to its large surface-to-volume ratio, tunable bandgap, flexibility, biocompatibility, promising physical, electronic and optical properties.This work started with the studies on the electrical and optical properties of Molybdenum Diselenide (MoSe2). Different from the currently established synthesis method, we applied an optimized exfoliation and transferring process to achieve large and thin layers of the material. Based on the acquired ultra-large nanosheet, transfer length measurement (TLM) was performed to examine the effect of layer thickness on its electrical and optical properties. The results provide guidance for selecting an optimal thickness of MoSe2 layers for electronic and optoelectronic applications.With the optimized layer thickness, an epidermal asthma-triggered gas sensor and a wearable gas sensor based on MoSe2 were demonstrated separately with distinct fabrication process, circuit design, platform and methods. The gas sensor was used to test NO2 and NH3, which exhibited high sensitivity, selectivity, low power consumption and room temperature operation property. The two systems were both incorporated with a Bluetooth embedded wireless connection in order to provide timely warnings, as well as storing cloud data so that the medical institute can easily access and provide an accurate diagnosis. The device data was finally used as a training model of the neuron network for predicting and searching for pollution sources.In order to further investigate 2D materials in the application of the health monitoring electronics, more physiological parameters were measured and obtained by a soft smart contact lens system with embedded sensors based on MoS2. In this design, a temperature sensor, a photodetector and a glucose sensor are placed on the surface of a contact lens for data collection from eyeballs and biomarkers in tears. The extremely soft mechanical property of the smart contact lens match with human eyes, which helps information acquisition under the epidermis. In this research, mechanical simulations of the device-curved surface attachment and in-vitro cytotoxicity tests were both examined for higher reliability performance.