High-sensitivity humidity sensing of microfiber coated with three-dimensional graphene network

We demonstrate a high-sensitivity relative humidity (RH) sensor based on microfiber coated with three-dimensional graphene network (3-DGN). The 3-DGN was fabricated by self-assembly of polystyrene (PS) microspheres which were each covered by reduced graphene oxide (rGO) nanosheets. The transmission electron microscopy (TEM) image and the Raman spectra indicated that the rGO nanosheets effectively covered the surface of each PS microsphere, with the 3D rGO network serving as the active material. Absorption of water molecules by the 3-DGN layer increases the effective refractive index of the 3-DGN cladding, leading to the decreasing of optical transmission power. Due to the high surface-to-volume ratios of the 3-DGN, which enhances its interaction with the water molecules, the sensor achieved a high linear humidity sensitivity of -4.118 dB/%RH over the humidity range 79.5-85.0 %RH and -0.224 dB/%RH over the range 50.5-70.6 %RH. Such high performance shows that the microfiber coated with 3-DGN has great potential for application in widespread fields, such as chemical and food processing and biology.