A conducting composite microfiber containing graphene/silver nanowires in an agarose matrix with fast humidity sensing ability

We report agarose-polymer-based composite microfibers with enhanced conductivity and fast humidity sensing owing to incorporation of conductive nanofillers. The microfibers are fabricated by extruding a hydrogel filament containing silver nanowires (AgNWs) and graphene oxide (GO, chemically reduced after extrusion) as 1D and 2D nanofillers, respectively. For the same concentration, GO enhances the mechanical properties of the microfibers more effectively than AgNWs. The microfiber with nanofillers has a higher Young's modulus than commercial nylon-6 and polyamide. Due to synergy between AgNWs and reduced GO (rGO), the microfiber with both fillers shows higher conductivity than those with only one filler. The flexible microfiber retains its conductivity well under repeated bending/unbending cycles. Since rGO ionizes water molecules, the conductivity of the microfiber increases with increasing environmental humidity. Humidity sensing ability of the composite microfiber, based on the humidity-dependent conductivity, is demonstrated. The microfiber with both nanofillers respond rapidly and reversibly to humidity changes because the AgNWs facilitate charge carrier transport and water adsorption/desorption. The humidity sensor based on the composite microfiber also reliably detects repeated short human breaths.