High sensitivity portable capacitive humidity sensor based on In2O3 nanocubes-decorated GO nanosheets and its wearable application in respiration detection

Portable humidity sensors fabricated in wearable devices have promising application in disease diagnostics and personal health monitoring. In this work, a capacitive humidity sensor based on indium oxide (In2O3) nano-cubes/graphene oxide (GO) nanosheets hybrid film was developed with Cu/Ni electrodes on an epoxy substrate. The In2O3/GO composite was analyzed through XRD, SEM, TEM and XPS for its composition, morphology and structure. The In2O3/GO film sensor was exposed to a wide range of relative humidity and its characteristics of capacitance performance with humidity were found to be better than humidity sensors based on pristine In2O3 or GO in terms of sensitivity, stability, response and recovery times. Meanwhile, a low-cost humidity and respiration monitoring system was developed on a print circuit board (PCB) based on STM32F405RGT6 micro-controller and Android Mobile APP. The curve of humidity and capacitance value can be shown on the smartphone, which can distinguish whether a person is breathing normally. The respiration detector designed holds great potential in the monitoring of asthma and irregular respiratory diseases due to its portability, instantaneity, accuracy and low power consumption.