Stretchable and transparent multimodal electronic-skin sensors in detecting strain, temperature, and humidity

Smart electronic skins (e-skins) have garnered extensive attentions owing to their potentials in health monitoring, human-machine interactions, and soft robotics. Herein, stretchable and transparent multimodal e-skin sensors composed of poly(vinyl alcohol) (PVA), citric acid (CA) and Ag nanoparticles (AgNPs) are developed by a simple in-situ reduction and solvent casting technology, which possess multiple sensing capabilities in strain, temperature and humidity. Although utilizing the nontransparent AgNPs as sensing components, the as-prepared PVA/CA/AgNPs sensor exhibits not only ultrahigh stretchability (up to 596% strain) but also outstanding transparency (the transmittance > 89%) attributed to the homogeneous dispersion of CA and AgNPs in PVA matrix. As flexible strain sensor, this sensor exhibits wide strain sensing range (1–200%), rapid response (90 ms), and excellent linearity of outputted signals (correlation coefficient: 0.998). Moreover, high-precision thermo-sensation (0.1 ℃) and outstanding temperature sensitivity (−0.076/℃ in the range of 30–40 ℃) make the sensor can detect subtle temperature variation. Furthermore, the good hygroscopicity of PVA and CA endows the fabricated sensor with outstanding humidity sensing performance, which can give human skin moisture information in real-time. More importantly, the designed sensor possesses excellent recyclability and can be reused for many times via the simple dissolution-reshaping treatment, which could reduce the electronical waste.