A highly sensitive humidity sensor based on an aggregation-induced emission luminogen-appended hygroscopic polymer microresonator

Self-assembled microspherical aggregates that work as whispering gallery mode (WGM) optical resonators are synthesized from a novel hygroscopic polymer covalently appended with an aggregation-induced emission luminogen. The resultant microspheres can absorb moisture from the surrounding atmosphere. Accordingly, the WGM resonant peaks shift due to the change in the diameter of the microsphere. The sensitivity of the peak-shift is as high as 255 picometre per percent relative humidity, which is the highest among non-tapered type optical humidity sensors. The responsivity toward moisture is kept virtually intact at least through five cycles of hydration and dehydration processes.