Figure 7.

(a–f) Pioneering works to monitor breath air in real time by using fast-response impedance-type humidity sensors. (a) Photo of humidity sensor using a spray-coated graphene oxide (GO) film and silver electrodes on a polyethylene naphthalate substrate. (b) Normalized response of humidity sensors dependent on the thickness of graphene oxides. The response of a commercial humidity sensor is shown as a reference. (c) Detection of breath air from speaking and breathing by using an ultrathin graphene oxide humidity sensor. Courtesy: Adapted with permission from ref. [54]. Copyright 2003 American Chemical Society. (d) Atomic force microscope image of a few nanofibers over electrodes. (e) Response of humidity sensor using a few nanofibers. (f) Respiratory monitoring by using a nanofiber humidity sensor in real time. The notations, e and i, refer to the exhaling and inhaling of the subject, respectively. Courtesy: Adapted with permission from ref. [64]. Copyright 2014 Springer Nature.