An ingenious strategy for improving humidity sensing properties of multi-walled carbon nanotubes via poly-L-lysine modification

Multi-walled carbon nanotubes (MWCNTs) as one of excellent conductive and poor-hydrophilicity materials are difficult to be directly used in humidity sensing field. In order to obtain MWCNTs with both good semiconducting characteristic and improved humidity sensing performances, MWCNTs composite film via poly-L-lysine (PLL) modification was developed for humidity detection. The humidity sensing properties of the as-fabricated sensor were investigated at room temperature (25 degrees C) within the relative humidity (RH) range from 0 to 91.5% RH. Due to abundant hydrophilic functional groups and conduction-blocking effect of PLL, the resistive-type humidity sensor based on MWCNTs/PLL film exhibits a good humidity sensing response of 659.97% at 91.5% RH. Especially, the resistance of the humidity sensor displays a clear positive humidity coefficient (PHC) that caused by the swelling effect of PLL. Finally, various potential applications of the humidity sensor were further performed for the real-time monitoring of skin humidity, baby diaper wetting, spatial humidity distribution and human exhaled breath, which provide an ingenious strategy for the practicability of the humidity sensor.