Photoacid-Loaded Nanopores of Hollow Mesoporous Organosilica Capsules for Fluorescent Humidity Sensing

Abstract

Humidity sensing has a wide application and receives intense attention from a broad spectrum of research areas. In this work, we demonstrated a robust humidity sensing strategy by loading photoacid HPTS (8-hydroxypyrene-1,3,6-trisulfonic acid, trisodium salt) into nanopores of hollow mesoporous organosilica (HMO) capsules. Taking advantage of the capillary condensation of nanopores, water vapor is enriched, which triggers the fluorescent color change of HPTS through intermolecular excited-state proton transfer (ESPT) for humidity sensing. The ESPT induced fluorescent color change behavior of HPTS loaded in nanopores was comprehensively investigated by using both steady and picosecond time-resolved fluorescence spectroscopy. The fabricated humidity sensors exhibit rapid response and recovery, qualified reversibility, and selectivity, which enable continuous monitoring of human respiration. Notably, the sensing performance, i.e., sensitivity and response range, can be effectively tuned by fabricating HMO capsules with properly sized nanopores, which provides an opportunity to design unique nanostructures of the humidity sensor for specific applications.