Spider dragline silk-based FP humidity sensor with ultra-high sensitivity

Abstract

We utilize the supercontraction property of spider dragline silk (SDS) to fabricate a Fabry-Perot (FP) humidity sensor whose FP cavity length can change up to 61.87% of the initial cavity length. Therefore, the sensor has ultra-high humidity sensitivity (up to 23.14 nm/%RH), because the change of cavity length determines the sensitivity of FP sensor. The FP interferometer consists of two reflective surfaces: the end of a single-mode fiber (SMF) and the glass plane coated with gold. The SMF is inserted into and fixed with a round quartz tube which is connected to two SDS-based humidity driven-muscles and two elastic blocks. Supercontraction property enables the SDS-based muscles to shrink axially in length in the environment with high relative humidity (RH). Under the contraction force of muscles, the fiber end will be pulled away from the gold-coated reflective plane when humidity increases. When the humidity decreases, the optical fiber driven by elastic force will be moved close to the gold-coated reflective plan, and the humidity-driven muscle will restore its original length. Therefore, the sensor can reversibly detect humidity. The average sensitivity of the sensor is 11.89 nm/%RH when humidity ranges from 32%RH to 95%RH, and the maximum sensitivity reaches 23.14 nm/%RH when RH varies from 32%RH to 55%RH. The sensor shows reversibility, good repeatability, little temperature crosstalk, and the potential to be applied in physiological detection such as respiratory monitoring.