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Biological and Medical Applications of Materials and Interfaces
A Stretchable and Highly Sensitive Optical Strain Sensor for Human-Activity Monitoring and Healthcare Jingjing Guo, Bingqian Zhou, Rui Zong, Longsheng Pan, Xuemei Li, Xinguang Yu, Changxi Yang, Lingjie Kong, and Qionghai Dai ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b09815 • Publication Date (Web): 29 Aug 2019 Downloaded from pubs.acs.org on August 30, 2019
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ACS Applied Materials & Interfaces
A Stretchable and Highly sensitive Optical Strain Sensor for Human-Activity Monitoring and Healthcare Jingjing Guo1, Bingqian Zhou1, Rui Zong2, Longsheng Pan2, Xuemei Li3, Xinguang Yu2, Changxi Yang1, Lingjie Kong1*, and Qionghai Dai4 1State
Key Laboratory of Precision Measurement Technology and Instruments, Department of
Precision Instruments, Tsinghua University, Beijing 100084, China 2Department 3Clinics
of Neurosurgery, Chinese PLA General Hospital, Beijing 100853, China
of Cadre, Department of Outpatient, Chinese PLA General Hospital, Beijing 100853,
China 4Department
of Automation, Tsinghua University, Beijing 100084, China
*
[email protected] Abstract: Flexible and stretchable strain sensors are essential to developing smart wearable devices for monitoring human activities. Such sensors have been extensively exploited with various conductive materials and structures, which, however, are normally in need of complex manufacturing processes and confronted with the challenge to achieve both large stretchability and high sensitivity. Here, we report a simple and low-cost optical strategy for the design of stretchable strain sensors, which are capable of measuring large strains of 100% with a low detection limit (±0.09%), at fast responsivity (40% strain).29-31 For example, Boland et al. reported a highly sensitive electronic strain sensor using graphene-polymer nanocomposites that could detect strains below 1%, but the sensor lost its electrical performances when stretched beyond 10%.31 Additionally, electronic sensors are highly sensitive to electromagnetic interferences (EMI), and they usually have a poor biocompatibility because of the usage of electrically conductive components, and suffer from electrical safety issues such as current leakage due to insufficient insulation.32 Optical sensors, especially fiber-optic sensors provide a promising alternative to electronic sensors, benefitting from their distinct advantages of high sensitivity, inherent electric safety, EMI
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ACS Applied Materials & Interfaces
immunity, and compact size.33 A previous work probed the ultimate limit of fiber-optic sensors that achieved strain measurements at the level of 10-13 ε.34 However, conventional fiber-optic sensors utilizing silica fibers are not competent for wearable sensing of human motions, due to their high stiffness and rigidity (maximum strain < 1%
35).
Recent attempts have been made to
enhance softness and stretchability of optical waveguides by using elastic polymers for wearable sensing applications.36-38 For example, a stretchable optical temperature sensor made by upconversion nanoparticles (UCNPs)-incorporated PDMS optical fibers was developed for wearable and continuous monitoring of body temperature.38 Despite recent developments in stretchable polymer-based waveguides and sensors, stretchable optical strain sensors for the detection of full-range human activities have not been demonstrated yet. The development of wearable optical strain sensors with simple readout (such as using a single photodiode), as well as having broad sensing range and fast response for full-range recognition of human activities could be a major step of wearable optics towards mobile healthcare. Here, we present a novel stretchable optical strain sensor (OS2) with a broad sensing range and high sensitivity that shows superior performances in the detection of both large-scale human motions and subtle biosignals. The OS2 is fabricated with a highly stretchable polydimethylsiloxane (PDMS) optical fiber of core/cladding step-index profile, whose core was incorporated with plasmonic gold nanoparticles (GNPs). This GNPs-PDMS fiber shows strong localized surface plasmon resonance (LSPR) effect that tensile strains could be quantified from the amount of absorption and scattering of light passing through the fiber. We thoroughly investigated the strain-sensing characteristics of the OS2 with a compact dual-laser optical setup, which enables readout of the sensor with a single photodiode. The OS2 shows a large sensing range up to 100% with a detection limit as low as ±0.09%, at fast responsivity (
