LAUSR

Flexible and stretchable strain sensors are essential components of 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 detection limit as low as ±0.09%, at fast responsivity (<12 ms) and high reproducibility (over 6000 cycles). The optical strain sensor (OS2) is fabricated by assembling plasmonic gold nanoparticles (GNPs) in stretchable polymer-based optical fibers, where a step-index core/cladding structure is adopted for effective light confinement. The stretchable, GNPs-incorporated optical fiber shows strong localized surface plasmon resonance (LSPR) effects that enables sensitive and reversible detection of strain deformations with high linearity and negligible hysteresis. The unique mechanical and sensing properties of the OS2 enable it to be assembled into clothing or directly mounted on human skins to detect diverse human activities from physiological signals as subtle as wrist pulses to large motions of joint bending and hand gestures. We further apply the OS2 for quantitative analysis of motor disorders such as that in Parkinson's disease (PD), and demonstrate its compatibility in strong electromagnetic interference environments during functional magnetic resonance imaging (fMRI), showing great promises for diagnostics and assessments of motor neuron diseases in clinics.