{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,17]],"date-time":"2026-07-17T03:49:23Z","timestamp":1784260163311,"version":"3.55.0"},"reference-count":43,"publisher":"MDPI AG","issue":"24","license":[{"start":{"date-parts":[[2025,12,12]],"date-time":"2025-12-12T00:00:00Z","timestamp":1765497600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"crossref","award":["62475109"],"award-info":[{"award-number":["62475109"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"crossref"}]},{"DOI":"10.13039\/501100004775","name":"Natural Science Foundation of Gansu Province, China","doi-asserted-by":"crossref","award":["24ZDFA006"],"award-info":[{"award-number":["24ZDFA006"]}],"id":[{"id":"10.13039\/501100004775","id-type":"DOI","asserted-by":"crossref"}]},{"DOI":"10.13039\/501100004775","name":"Natural Science Foundation of Gansu Province, China","doi-asserted-by":"crossref","award":["25JRRA649"],"award-info":[{"award-number":["25JRRA649"]}],"id":[{"id":"10.13039\/501100004775","id-type":"DOI","asserted-by":"crossref"}]},{"name":"Special Fund Project for Central Guiding Local Science and Technology Development","award":["24ZYQA050"],"award-info":[{"award-number":["24ZYQA050"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>Humidity monitoring is essential in industrial and scientific scenarios, yet remains challenging for compact EMI (electromagnetic interference)-immune sensors with high sensitivity and robust stability. A novel fiber Bragg grating (FBG) humidity sensor was developed, which incorporated LiCl@UIO-66 microfillers within a poly(N-isopropylacrylamide) (PNIPAM) hydrogel matrix. Structural characterization using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier-transform infrared (FTIR) spectroscopy confirms that LiCl is confined or nanodispersed within intact UIO-66, and that interfacial ion\u2013dipole\/hydrogen-bonding exists between the composite and water. Systematic variation in coating time (30\u2013720 min) reveals monotonic growth of the total wavelength shift with diminishing returns. A coating time of 4 h was found to yield a wavelength shift of approximately 0.38\u20130.40 nm, representing about 82% of the maximum shift observed at 12 h, while maintaining good quasi-linearity and favorable kinetics. Calibration demonstrates sensitivities of 6.7 pm\/%RH for LiCl@UIO-66_33 and 10.6 pm\/%RH for LiCl@UIO-66_51 over ~0\u201395%RH. Stepwise tests show response times t90 of \u224814 min for both composites, versus \u224830 min for UIO-66 and \u224855 min for neat PNIPAM. Long-term measurements on the 51 wt.% device are stable over the first ~20 days, with only slow drift thereafter, and repeated humidity cycling is reversible. The wavelength decreases monotonically during drying while settling time increases toward low RH. The synergy of hydrogel\u2013MOF\u2013salt underpins high sensitivity, accelerated transport, and practical stability, offering a scalable route to high-performance optical humidity sensing.<\/jats:p>","DOI":"10.3390\/ma18245587","type":"journal-article","created":{"date-parts":[[2025,12,12]],"date-time":"2025-12-12T11:13:33Z","timestamp":1765538013000},"page":"5587","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Development of a High-Sensitivity Humidity Sensor Using Fiber Bragg Grating Coated with LiCl@UIO-66-Doped Hydrogel"],"prefix":"10.3390","volume":"18","author":[{"given":"Binxiaojun","family":"Liu","sequence":"first","affiliation":[{"name":"The National Engineering Research Center of Fiber Optic Sensing Technology and Network, Wuhan University of Technology, Wuhan 430070, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zelin","family":"Gao","sequence":"additional","affiliation":[{"name":"School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Runqi","family":"Yao","sequence":"additional","affiliation":[{"name":"School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1625-6145","authenticated-orcid":false,"given":"Liyun","family":"Ding","sequence":"additional","affiliation":[{"name":"The National Engineering Research Center of Fiber Optic Sensing Technology and Network, Wuhan University of Technology, Wuhan 430070, China"},{"name":"School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0001-5052-7359","authenticated-orcid":false,"given":"Xusheng","family":"Xia","sequence":"additional","affiliation":[{"name":"The National Engineering Research Center of Fiber Optic Sensing Technology and Network, Wuhan University of Technology, Wuhan 430070, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,12,12]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"280","DOI":"10.1016\/j.sna.2008.01.017","article-title":"Fibre-optic sensor technologies for humidity and moisture measurement","volume":"144","author":"Yeo","year":"2008","journal-title":"Sens. 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