A general strategy for MOFs coupled to optical fiber for highly sensitive humidity sensing

To achieve real‐time and high‐sensitive humidity sensing, a universal method was developed to allow arbitrary nanocrystals to be attached to the end of an optical fiber, further producing an effective interference spectrum. To validate this approach, four classical metal–organic framework (MOF) materials (ZIF‐8, UiO‐66, HKUST‐1, MIL‐101) are connected to the end of a single‐mode optical fiber by this connection method to form humidity sensors. According to the Fabry–Perot interference principle, the change in humidity causes the optical path difference of the Fabry–Perot cavity, which further shifts the interference spectral peaks. High‐sensitive humidity sensing performance was achieved by monitoring the spectral change in relation to humidity. The best‐performing optical fiber sensor based on MIL‐101 exhibits a sensitivity of 5.30 nm/%RH and shows excellent circulation and stability. This tiny integrated structure is effectively resistant to electromagnetic interference as well as temperature disturbances, which is of importance for real‐time and sensitive humidity detection in extreme environments.