Denatured bovine serum albumin particle decorated graphene oxide nanocomposite for ultrasensitive resistive humidity sensing†

From humidity monitoring in various fields to noncontact human–machine interactions, the application of humidity sensors has been expanding. Accordingly, better resolution and higher sensitivity are desired for improving the performance of humidity sensors. In this study, an electrical sensor for highly sensitive humidity detection was fabricated via hydrogen bonding by integrating denatured bovine serum albumin particles (dBSA) with proton conductivity and graphene oxide (GO) nanosheets with large specific surface areas. The current signal of the sensor exhibits an approximately semi-logarithmic linear relationship with the relative humidity (RH), showing a nearly seven order of magnitude increase in current over the RH range of 15% to 90%. The sensor also displays high stability, selectivity, and response rate within a few seconds. The dBSA–GO nanofilm based humidity sensor was successfully applied to monitor respiration rates and simulate human–machine interaction in real time with high accuracy. Impedance spectroscopy and Kelvin probe measurements revealed the changes in the capacitance and work function of the dBSA–GO nanofilm with water adsorption. The water penetrating into the dBSA–GO nanofilm forms extensive hydrogen bonding networks, enhancing proton conductivity, while water adsorption on the surface alters dipole moments, resulting in asymmetric current behavior with increased current at forward bias. The extremely high humidity response shows the great potential of proteins in humidity sensor applications, thus expanding the field of biocompatible humidity sensors.