Silk Fibroin‐Regulated Nanochannels for Flexible Hydrovoltaic Ion Sensing

Abstract The evaporation‐induced hydrovoltaic effect based on ion‐selective nanochannels can theoretically be employed for high‐performance ion sensing; yet, the indeterminate ion‐sensing properties and the acquisition of high sensing performance are rarely explored. Herein, a controllable nanochannel regulation strategy for flexible hydrovoltaic devices with highly sensitive ion‐sensing abilities is presented across a wide concentration range. By multiple dip‐coating of silk fibroin (SF) on an electrospinning nylon‐66 nanofiber (NNF) film, the surface polarity enhancement, the fibers size regulation with a precision of ≈25 nm, and the nanostructure firm binding are achieved simultaneously. The resultant flexible freestanding hydrovoltaic device exhibits an open circuit voltage up to 4.82 V in deionized water, a wide ion sensing range of 10 −7 to 10 0 m, and ultrahigh sensitivity as high as 1.37 V dec −1 , which is significantly higher than the sensitivity of the traditional solid‐contact ion‐selective electrodes (SC‐ISEs). The fabricated flexible ion‐sensitive hydrovoltaic device is successfully applied for wearable human sweat electrolyte sensing and for environmental trace‐ion monitoring, thereby confirming the potential application of the hydrovoltaic effect for ion sensing.