Graphene oxide wrapped-silica microspheres humidity sensor with fast response/recovery, high sensitivity, and selectivity for pig respiratory rate monitoring

Respiratory rate monitoring is of great significance in pig healthy breeding for the early detection and timely prevention of respiratory diseases. Humidity sensing is an important noncontact method to monitor pig respiration, which does not cause direct harm to pigs and meets the requirements of animal welfare. This paper proposes a humidity sensor based on graphene oxide wrapped-silica microspheres（GO@SiO2）. First, the sensor shows fast response/recovery performances of0.24/0.73 s. Experiments demonstrate that the wrapped microsphere structure can inhibit water aggregation. It is speculated that the wrapped microsphere structure can inhibit the stacking of GO, and its curved surface can promote the evaporation of water molecules. Second, the sensor shows a high sensitivity of 1.2%/%RH–4.2%/%RH in 11%–95% RH range. This can be attributed to different sensing mechanisms, from hopping transport to increasing ion transport, leading to a significant change in the sensor's resistance. Third, the sensor shows selectivity to water molecules due to the hydrophilic characteristic of GO and the significant increase in conductivity by ion transport. Finally, the sensor is applied to realize the respiratory rate monitoring of adult pigs and piglets.