Humidity-sensitive CsPbBr3 perovskite based photoluminescent sensor for detecting Water content in herbal medicines

Excessive water in herbal medicines (HMs) can cause pests infestation, mildew, and decomposition of active ingredients during storage. The classical detection methods for water content are still unsatisfactory due to the requirement of sophisticated manipulation, long time consumption and usage of large amounts of toxic toluene. Herein, hot injection method was adopted to synthesize humidity-sensitive CsPbBr3 perovskite, which was used to develop a novel photoluminescent (PL) sensor on a paper substrate for rapid detection of water content in HMs with a turn-off mode. Due to the strong ionic nature of CsPbBr3 and the high aqueous solubility of CsBr, CsPbBr3 perovskite is very unstable upon the exposure of water. The signal off can be attributed to the phase change from luminescent CsPbBr3 to non-luminescent CsPb2Br5 according to the results of XRD pattern analysis of CsPbBr3 perovskite before and after water exposure. The PL intensity of CsPbBr3 is linearly related to the water content within the range of 1–17 %. For Seutellaria baicalensis and Astragalus flavone, the detection limits are 0.75 % and 0.67 %, respectively. The results of recovery tests for the two HMs are within the range of 96.7–102.5 %. This work realizes the application of CsPbBr3 perovskite in the field of pharmaceutical analysis, and shows the application potential for the control of water content in other types of samples sensitive to humidity.