Highly responsive humidity sensor based on Ag doped polyindole/hydroxyethyl cellulose nanocomposites for monitoring human physiological activities

A highly sensitive humidity sensor based on Ag doped polyindole/hydroxyethyl cellulose (Ag-PIn/HEC) composite is constructed for relative humidity sensing at room temperature in this study. Doping of Ag and HClO 4 is used to solve the problem of poor electrical conductivity of polyindole (PIn). The humidity sensitive material is prepared by the combination of HEC binder and doped PIn, which realizes the high sensitivity humidity detection. The Ag-PIn/HEC sensor showed high response value (93800 %), good linearity (R 2  = 0.993), fast response time (8 s), low humidity hysteresis (4.16 %), good reproducibility, and stability over a detection range of 11 ∼ 84 % relative humidity (RH). In addition, the humidity sensor has a specific response to human breath. According to the change of impedance signals, it can easily distinguish between oral and nasal breathing as well as light or rapid breathing, which can be used in medical care, such as preventive monitoring for special groups (asthma patients). Moreover, the sensor can recognize certain simple words by detecting changes in exhalation while speaking, which provides potential applications in speech recognition and non-contact switches.