{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,9]],"date-time":"2026-01-09T02:08:49Z","timestamp":1767924529389,"version":"3.49.0"},"reference-count":32,"publisher":"MDPI AG","issue":"1","license":[{"start":{"date-parts":[[2015,12,29]],"date-time":"2015-12-29T00:00:00Z","timestamp":1451347200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>An on-chip optical humidity sensor using Nano-anatase TiO2 coating is presented here. The coating material was prepared so that the result is in solution form, making the fabrication process quick and simple. Then, the solution was effortlessly spin-coated on an SU8 straight channel waveguide. Investigating the sensitivity and performance (response time) of the device revealed a great linearity in the wide range (35% to 98%) of relative humidity (RH). In addition, a variation of more than 14 dB in transmitted optical power was observed, with a response time of only ~0.7 s. The effect of coating concentration and UV treatment was examined on the performance and repeatability of the sensor. Interesting observations were found, and the attributed mechanisms were described. In addition, the proposed sensor was extensively compared with other state-of-the-art proposed counterparts from the literature and remarkable advantages were found. Since a high sensitivity of ~0.21 dB\/%RH and high dynamic performances were demonstrated, this sensor is proposed for use in biomedical applications.<\/jats:p>","DOI":"10.3390\/s16010039","type":"journal-article","created":{"date-parts":[[2015,12,29]],"date-time":"2015-12-29T10:00:08Z","timestamp":1451383208000},"page":"39","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":31,"title":["Nano-Anatase TiO2 for High Performance Optical Humidity Sensing on Chip"],"prefix":"10.3390","volume":"16","author":[{"given":"Mahdiar","family":"Ghadiry","sequence":"first","affiliation":[{"name":"Photonics Research Center, University of Malaya, Kuala Lumpur 50603, Malaysia"}]},{"given":"Mehrdad","family":"Gholami","sequence":"additional","affiliation":[{"name":"Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia"}]},{"given":"Lai","family":"Choon Kong","sequence":"additional","affiliation":[{"name":"Photonics Research Center, University of Malaya, Kuala Lumpur 50603, Malaysia"}]},{"given":"Chong","family":"Wu Yi","sequence":"additional","affiliation":[{"name":"Photonics Research Center, University of Malaya, Kuala Lumpur 50603, Malaysia"}]},{"given":"Harith","family":"Ahmad","sequence":"additional","affiliation":[{"name":"Photonics Research Center, University of Malaya, Kuala Lumpur 50603, Malaysia"}]},{"given":"Yatima","family":"Alias","sequence":"additional","affiliation":[{"name":"Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia"}]}],"member":"1968","published-online":{"date-parts":[[2015,12,29]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"6070","DOI":"10.1021\/ja070788m","article-title":"High-Sensitivity Humidity Sensor Based on a Single SnO2 Nanowire","volume":"129","author":"Kuang","year":"2007","journal-title":"J. Am. Chem. Soc."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"76","DOI":"10.1016\/S0925-4005(01)00538-X","article-title":"Optical waveguide humidity sensor with symetric multilayer configuration","volume":"75","author":"Ren","year":"2001","journal-title":"Sens. Actuators B"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"587","DOI":"10.1109\/JLT.2011.2106479","article-title":"Fiber Optic Sensors in Structural Health Monitoring","volume":"29","author":"Cobo","year":"2011","journal-title":"J. Lightwave Technol."},{"key":"ref_4","unstructured":"Cocatre-Zilgien, J.H. (2000). Aircraft System Monitoring Air Humidity to Locate Updrafts. (US6012675A), US Patent."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"212","DOI":"10.1016\/j.apsusc.2004.08.013","article-title":"Zinc oxide nanorod and nanowire for humidity sensor","volume":"242","author":"Zhang","year":"2005","journal-title":"Appl. Surface Sci."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"330","DOI":"10.1016\/S0040-6090(97)00146-6","article-title":"Humidity sensor using planar optical waveguides with claddings of various oxide materials","volume":"305","author":"Ansari","year":"1997","journal-title":"Th. Sol. Film."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"281","DOI":"10.1109\/JSEN.2008.917487","article-title":"Optical fiber humidity sensors using nanostructured coatings of SiO nanoparticles","volume":"8","author":"Corres","year":"2008","journal-title":"IEEE J. Sens."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"11166","DOI":"10.1021\/nn404889b","article-title":"Ultrafast Graphene Oxide Humidity Sensors","volume":"7","author":"Borini","year":"2013","journal-title":"ACS Nano"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"521","DOI":"10.1016\/0925-4005(93)85297-N","article-title":"Sensitivity improvment for evanscent-wave gas sensors","volume":"11","author":"Stewart","year":"1993","journal-title":"Sens. Actuators B Chem."},{"key":"ref_10","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. Actuators A Phys."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1038\/srep04103","article-title":"Ultrafast response humidity sensor using supramolecular nanofibre and its application in monitoring breath humidity and flo","volume":"4","author":"Mogera","year":"2014","journal-title":"Sci. Rep."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1038\/srep02714","article-title":"Ultrahigh humidity sensitivity of graphene oxide","volume":"3","author":"Bi","year":"2013","journal-title":"Sci. Rep."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"4","DOI":"10.1088\/0268-1242\/30\/4\/045012","article-title":"A new approach to model sensitivity of graphene-based gas sensors","volume":"30","author":"Ghadiry","year":"2015","journal-title":"Semicond. Sci. Technol."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"1133","DOI":"10.1007\/s11468-015-9905-6","article-title":"Sensitivity Modelling of Graphene Nanoscroll-Based NO2 Gas Sensors","volume":"10","author":"Khaledian","year":"2015","journal-title":"Plasmonics"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"314","DOI":"10.1016\/j.yofte.2014.03.008","article-title":"Optical fiber relative-humidity sensor with evaporated dielectric coating on fiber end-face","volume":"20","author":"Xie","year":"2014","journal-title":"Opt. Fiber Technol."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"11090","DOI":"10.1364\/OE.22.011090","article-title":"Graphene oxide-based waveguide polariser: From thin film to quasi-bulk","volume":"22","author":"Lim","year":"2014","journal-title":"Opt. Express"},{"key":"ref_17","unstructured":"Mathew, J. (2013). Development of Novel Fiber Optic Humidity Sensors and Their Derived Applications. [Master\u2019s Thesis, Dublin Institute of Technology]."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"5877","DOI":"10.1021\/am500777b","article-title":"Underestanding water permeation in graphene oxide membranes","volume":"6","author":"Wei","year":"2014","journal-title":"Appl. Mater. Interfaces"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"310","DOI":"10.1016\/j.snb.2011.03.035","article-title":"Carbon dioxide gas sensor using a graphene sheet","volume":"157","author":"Yoon","year":"2011","journal-title":"Sens. Actuators B Chem"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"8269","DOI":"10.1143\/JJAP.44.8269","article-title":"TiO2 photocatalysis: A historical overview and future prospects","volume":"44","author":"Hashimoto","year":"2015","journal-title":"Jpn. J. Appl. Phys."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"10696","DOI":"10.1021\/jp0357830","article-title":"Enhancement of photoinduced highly hydrophilic conversion on TiO2 thin films by introducing tensile stress","volume":"107","author":"Shibata","year":"2003","journal-title":"J. Phys. Chem. B"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"2009","DOI":"10.1021\/nl061197h","article-title":"Ultrasensitive chemiresistors based on electrospun TiO2 nanofibers","volume":"6","author":"Kim","year":"2006","journal-title":"Nano Lett."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"16049","DOI":"10.1039\/c1jm11937k","article-title":"Enhanced gas sensing performance of TiO2 functionalized magneto-optical SPR sensors","volume":"21","author":"Manera","year":"2011","journal-title":"J. Mater. Chem."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"24329","DOI":"10.3390\/s141224329","article-title":"All-Optical Graphene Oxide Humidity Sensors","volume":"14","author":"Lim","year":"2014","journal-title":"Sensors"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"52","DOI":"10.1109\/JSEN.2003.822214","article-title":"High-sensitivity sensor of low relative humidity based on overlay on side-polished fibers","volume":"4","author":"Guerrero","year":"2004","journal-title":"IEEE J. Sens."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"2164","DOI":"10.1364\/AO.51.002164","article-title":"Titanium dioxide nanoparticle based optical fiber humidity sensor with linear response and enhanced sensitivity","volume":"51","author":"Aneesh","year":"2012","journal-title":"Appl. Opt."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"5310","DOI":"10.1364\/AO.50.005310","article-title":"Zinc oxide nanoparticle based optical fiber humidity sensor having linear response throughout a large dynamic range","volume":"50","author":"Aneesh","year":"2011","journal-title":"Appl. Opt."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"148","DOI":"10.1016\/j.snb.2005.01.033","article-title":"Characterisation of a polymer-coated fibre Bragg grating sensor for relative humidity sensing","volume":"110","author":"Yeo","year":"2005","journal-title":"Sens. Actuators B Chem."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"806","DOI":"10.1109\/JSEN.2003.820349","article-title":"Evanescent wave optical-fiber sensing (temperature, relative humidity, and pH sensors)","volume":"3","author":"Gaston","year":"2003","journal-title":"IEEE J. Sens."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"335","DOI":"10.1016\/j.snb.2005.02.012","article-title":"High relative humidity measurements using gelatin coated long-period grating sensors","volume":"110","author":"Tan","year":"2005","journal-title":"Sens. Actuators B Chem."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"880","DOI":"10.1109\/LPT.2007.897551","article-title":"Long-period grating relative humidity sensor with hydrogel coating","volume":"19","author":"Liu","year":"2007","journal-title":"IEEE Photonics Technol. Lett."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"106","DOI":"10.1016\/j.snb.2007.07.113","article-title":"Optical fibre based humidity sensor using co-polyaniline clad","volume":"129","author":"Vijayan","year":"2008","journal-title":"Sens. Actuators B Chem."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/16\/1\/39\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T20:54:59Z","timestamp":1760216099000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/16\/1\/39"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2015,12,29]]},"references-count":32,"journal-issue":{"issue":"1","published-online":{"date-parts":[[2016,1]]}},"alternative-id":["s16010039"],"URL":"https:\/\/doi.org\/10.3390\/s16010039","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2015,12,29]]}}}