Polysquaramides: Rapid and stable humidity sensing for breath monitoring and morse code communication

Abstract Breath monitoring is an efficient way to evaluate human health but rather challenging if using humidity sensors, because the response and recovery time should be as short as seconds to catch up the breath rate and the sensor needs to be of long-term stability under stress of exhaled flow. Various conjugated polymer materials have been applied in humidity sensors successfully, but their long-term stability need to be improved while response/recovery time need to be shortened. Herein, we fabricated two humidity sensors based on ion-in-conjugation polysquaramides poly (1,5-diaminoanthraquinone-squarine) (1,5-PDAS) and poly (2,6-diaminoanthraquinone-squarine) (2, 6-PDAS), respectively. The humidity sensor shows rapid response/recovery time less than 2 s/1 s and is stable under ambient atmosphere at least for thirty days. Taking these advantages, polysquaramide-based humidity sensor is designed for breath monitoring for the first time. Deep/shallow and fast/slow respiration were distinguished and recorded remotely. The Morse coding/sending/receiving/decoding was further demonstrated, indicating the potential application of polysquaramides in future humidity monitoring system.