Superhydrophilic, Underwater Superoleophobic, and Highly Stretchable Humidity and Chemical Vapor Sensors for Human Breath Detection.

Humidity and chemical vapor sensors have promising applications in the field of environment protection, human healthcare, and so forth. It is still challenging to develop sensor materials that can serve as both humidity and chemical vapor sensors with high sensitivity, low detection limit, and excellent stretchability, repeatability, and reliability. In this study, a flexible, stretchable, and conductive nanofiber composite (CNC) with superhydrophilicity and underwater superoleophobicity is prepared by acidified carbon nanotube (ACNT) decoration onto the thermoplastic polyurethane (PU) nanofiber surface. ACNT introduction increases both the Young's modulus and tensile strength and almost maintains the superelasticity of the PU nanofibrous membrane. The as-obtained CNC could be used to detect both moisture and chemical vapors. When used as the humidity sensor, ACNTs can absorb surrounding water molecules and thus increase their resistance. On the other hand, the PU can be swollen by different chemical vapors, which can, to a different extent, damage the conductive network inside the composite and cause the increase of the composite resistance. The CNC can be integrated with a mask for real-time detection of human respiration. The CNC-based chemical vapor sensor possesses low detection limit, quick response, good selectivity, and excellent recyclability (even in a high humid environment) and has potential applications in monitoring biomarker gases from human breath.