期刊
ACS APPLIED NANO MATERIALS
卷 2, 期 4, 页码 2222-2229出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsanm.9b00174
关键词
wearable sensor; strain sensor; graphene; metallic nanoislands; sleep apnea
资金
- National Institutes of Health Director's New Innovator Award [1DP2EB022358]
- National Science Foundation Graduate Research Fellowship Program [DGE-1144086]
- Center for Wearable Sensors in the Jacobs School of Engineering at the University of California, San Diego
- Qualcomm
- Sabic
- Cubic
- Dexcom
- Corning
- Honda
- Samsung
- Sony
- Initiative for Maximizing Student Development (IMSD) program - National Institute of General Medical Sciences [R25GM083275]
- National Science Foundation [ECCS-1542148]
Wearable mechanical sensors have the potential to transform healthcare by enabling patient monitoring outside of the clinic. A critical challenge in the development of mechanical-e.g., strain-sensors is the combination of sensitivity, dynamic range, and robustness. This work describes a highly sensitive and robust wearable strain sensor composed of three layered materials: graphene, an ultrathin film of palladium, and highly plasticized PEDOT:PSS. The role of the graphene is to provide a conductive, manipulable substrate for the deposition of palladium. When deposited at low nominal thicknesses (similar to 8 nm), palladium forms a rough, granular film which is highly piezoresistive (i.e., the resistance increases with strain with high sensitivity). The dynamic range of these graphene/palladium films, however, is poor and can only be extended to similar to 10% before failure. This fragility renders the films incompatible with wearable applications on stretchable substrates. To improve the working range of graphene/palladium strain sensors, a layer of highly plasticized PEDOT:PSS is used as a stretchable conductive binder. That is, the conductive polymer provides an alternative pathway for electrical conduction upon cracking of the palladium film and the graphene. The result was a strain sensor that possessed good sensitivity at low strains (0.001% engineering strain) but with a working range up to 86%. The piezoresistive performance can be optimized in a wearable device by sandwiching the conductive composite between a soft PDMS layer in contact with the skin and a harder layer at the air interface. When attached to the skin of the torso, the patch-like strain sensors were capable of detecting heartbeat (small strain) and respiration (large strain) simultaneously. This demonstration highlights the ability of the sensor to measure low and high strains in a single interpolated signal, which could be useful in monitoring, for example, obstructive sleep apnea with an unobtrusive device.
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