{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,23]],"date-time":"2026-08-23T04:22:14Z","timestamp":1787458934005,"version":"build-2736575974"},"reference-count":25,"publisher":"MDPI AG","issue":"16","license":[{"start":{"date-parts":[[2026,8,21]],"date-time":"2026-08-21T00:00:00Z","timestamp":1787270400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100015330","name":"State Grid Jiangsu Electric Power Co., Ltd.","doi-asserted-by":"crossref","award":["J2025071"],"award-info":[{"award-number":["J2025071"]}],"id":[{"id":"10.13039\/501100015330","id-type":"DOI","asserted-by":"crossref"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Methanol is a critical molecular marker for the early aging of oil-paper insulation, and its rapid detection is highly valuable for insulation condition assessment and the fault warning of power transformers. Widely used chromatographic methods require sophisticated pretreatment workflow and are not suitable for in situ monitoring. Non-destructive spectroscopic methods remain challenging due to the intrinsically small cross section of trace molecules in complex liquid environments. The rapid, direct detection of trace methanol in an oil mixture has yet to be demonstrated. In this study, a high-performance Raman-enhancing substrate was developed through hierarchical microstructure regulation, combining microscale light-trapping structures and nanoscale field-confinement sites to sense the weak Raman response of methanol in transformer oil. Direct detection of ppm-level methanol in the oil matrix was achieved, without additional adsorption enrichment or other complicated pretreatment procedures. The characteristic Raman band of methanol in transformer oil was identified, and a quantitative sensing method was established. Furthermore, the intrinsic temperature-dependent Raman response of methanol was investigated to evaluate the stability of its characteristic fingerprint bands over a broad temperature range. This work demonstrates a rapid, sensitive, and pretreatment-free spectroscopic strategy for trace methanol detection in complex oil matrices, and also sheds light on the high-sensitivity detection of small molecular markers in complex liquid environments.<\/jats:p>","DOI":"10.3390\/s26165291","type":"journal-article","created":{"date-parts":[[2026,8,21]],"date-time":"2026-08-21T08:14:01Z","timestamp":1787300041000},"page":"5291","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Plasmonic Field-Enhanced Raman Sensing Enables Rapid Trace Methanol Detection in Transformer Oil"],"prefix":"10.3390","volume":"26","author":[{"given":"Xiaoqin","family":"Zhang","sequence":"first","affiliation":[{"name":"Electric Power Research Institute of State Grid Jiangsu Electric Power Co., Ltd., Nanjing 211103, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hongbin","family":"Zhu","sequence":"additional","affiliation":[{"name":"Electric Power Research Institute of State Grid Jiangsu Electric Power Co., Ltd., Nanjing 211103, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hao","family":"Liu","sequence":"additional","affiliation":[{"name":"College of Engineering and Applied Sciences, Nanjing University, Nanjing 210026, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jin","family":"Cao","sequence":"additional","affiliation":[{"name":"College of Engineering and Applied Sciences, Nanjing University, Nanjing 210026, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Han","family":"Shi","sequence":"additional","affiliation":[{"name":"College of Engineering and Applied Sciences, Nanjing University, Nanjing 210026, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Shanyuan","family":"Niu","sequence":"additional","affiliation":[{"name":"College of Engineering and Applied Sciences, Nanjing University, Nanjing 210026, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,8,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1442","DOI":"10.1016\/j.rser.2017.05.165","article-title":"Causes of Transformer Failures and Diagnostic Methods\u2014A Review","volume":"82","author":"Christina","year":"2018","journal-title":"Renew. Sustain. Energy Rev."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"111347","DOI":"10.1016\/j.rser.2021.111347","article-title":"Advances in DGA Based Condition Monitoring of Transformers: A Review","volume":"149","author":"Wani","year":"2021","journal-title":"Renew. Sustain. Energy Rev."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"5786","DOI":"10.1109\/JSEN.2017.2735193","article-title":"Chemical Sensing Strategies for Real-Time Monitoring of Transformer Oil: A Review","volume":"17","author":"Sun","year":"2017","journal-title":"IEEE Sens. J."},{"key":"ref_4","first-page":"192","article-title":"Prediction of concentration for dissolved gas in oil based on CEEMDAN and TCN","volume":"43","author":"Zhang","year":"2024","journal-title":"Electr. Power Eng. Technol."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"295","DOI":"10.1007\/s10570-007-9124-1","article-title":"Identification of a Chemical Indicator of the Rupture of 1,4-\u03b2-Glycosidic Bonds of Cellulose in an Oil-Impregnated Insulating Paper System","volume":"14","author":"Jalbert","year":"2007","journal-title":"Cellulose"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"3625","DOI":"10.1109\/TDEI.2015.005386","article-title":"Relationships between Methanol Marker and Mechanical Performance of Electrical Insulation Papers for Power Transformers under Accelerated Thermal Aging","volume":"22","author":"Arroyo","year":"2015","journal-title":"IEEE Trans. Dielectr. Electr. Insul."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"13","DOI":"10.1016\/j.proeng.2017.09.690","article-title":"The Research of Methanol Generation in Aging Paper Insulation","volume":"202","author":"Darian","year":"2017","journal-title":"Procedia Eng."},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Jalbert, J., Rodriguez-Celis, E.M., Arroyo-Fern\u00e1ndez, O.H., Duchesne, S., and Morin, B. (2019). Methanol Marker for the Detection of Insulating Paper Degradation in Transformer Insulating Oil. Energies, 12.","DOI":"10.3390\/en12203969"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"1955","DOI":"10.1049\/gtd2.12784","article-title":"A Review on a Novel Method for Aging Evaluation of Transformer Insulating Paper Based on Methanol","volume":"17","author":"Chen","year":"2023","journal-title":"IET Gener. Transm. Distrib."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"240","DOI":"10.1016\/j.chroma.2012.07.069","article-title":"Robust and Sensitive Analysis of Methanol and Ethanol from Cellulose Degradation in Mineral Oils","volume":"1256","author":"Jalbert","year":"2012","journal-title":"J. Chromatogr. A"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1081","DOI":"10.1007\/s10337-014-2650-8","article-title":"GC Methods for the Determination of Methanol and Ethanol in Insulating Mineral Oils as Markers of Cellulose Degradation in Power Transformers","volume":"77","author":"Bruzzoniti","year":"2014","journal-title":"Chromatographia"},{"key":"ref_12","first-page":"27","article-title":"Application of Experimental Design for Determination of Methanol and Ethanol in Transformer Industrial Oils Using Headspace Single-Drop Microextraction","volume":"8","author":"Bokhon","year":"2020","journal-title":"Anal. Bioanal. Chem. Res."},{"key":"ref_13","first-page":"30","article-title":"Temperature and Pressure Characteristics of a Photothermal Interference Detection System for Dissolved Acetylene in Transformer Oil","volume":"42","author":"Wu","year":"2023","journal-title":"Electr. Power Eng. Technol."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"124333","DOI":"10.1016\/j.saa.2024.124333","article-title":"Simultaneous Detection of Multiple Aging Characteristic Components in Oil-Paper Insulation Using Sensitive Raman Technology and Microfluidics","volume":"318","author":"Song","year":"2024","journal-title":"Spectrochim. Acta Part A Mol. Biomol. Spectrosc."},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Gu, Z., Chen, W., Xiang, Y., Du, L., Wan, F., and Zhao, L. (2016, January 19\u201322). Detection of Methanol Dissolved in Transformer Oil by Laser Raman Spectroscopy. Proceedings of the 2016 IEEE International Conference on High Voltage Engineering and Application (ICHVE), Chengdu, China.","DOI":"10.1109\/ICHVE.2016.7800729"},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Zhang, S., Chen, W., Wan, F., Shi, H., Zhou, W., Zhang, J., and Zhu, C. (2019, January 23\u201327). A SERS Substrate for Detecting Methanol in Transformer Oil. Proceedings of the 2019 IEEE 20th International Conference on Dielectric Liquids (ICDL), Rome, Italy.","DOI":"10.1109\/ICDL.2019.8796557"},{"key":"ref_17","first-page":"6955","article-title":"Theoretical Studies of the Influence of an Intermolecular Force and an Electric Field on the Methanol Raman Spectrum","volume":"124","author":"Zhang","year":"2020","journal-title":"J. Phys. Chem. C"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"154442","DOI":"10.1016\/j.apsusc.2022.154442","article-title":"Derivatization Reaction-Based Surface-Enhanced Raman Scattering for Detection of Methanol in Transformer Oil Using Ag\/ZnO Composite Nanoflower Substrate","volume":"604","author":"Chen","year":"2022","journal-title":"Appl. Surf. Sci."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"861","DOI":"10.1007\/s42835-019-00097-x","article-title":"Detection of Methanol in Power Transformer Oil Using Spectroscopy","volume":"14","author":"Fu","year":"2019","journal-title":"J. Electr. Eng. Technol."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"828","DOI":"10.1002\/tee.23124","article-title":"Concentration of 5-hydroxymethylfurfural Produced by Insulating Paper in an Oil\u2013Paper Insulation System","volume":"15","author":"Chen","year":"2020","journal-title":"IEEJ Trans. Electr. Electron. Eng."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"136","DOI":"10.1109\/TDEI.2023.3307648","article-title":"Analysis of Methanol in Transformer Oil Based on Extraction and Silver Nanosubstrate","volume":"31","author":"Zhang","year":"2024","journal-title":"IEEE Trans. Dielectr. Electr. Insul."},{"key":"ref_22","first-page":"192","article-title":"Transformer Fault Diagnosis Method Based on Characteristic Quantity Screening of Dissolved Gases in Oil","volume":"43","author":"Liao","year":"2024","journal-title":"Electr. Power Eng. Technol."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"110127","DOI":"10.1016\/j.microc.2024.110127","article-title":"Recent Advances in Ratiometric Surface-Enhanced Raman Spectroscopy Sensing Strategies","volume":"199","author":"Wu","year":"2024","journal-title":"Microchem. J."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"2569","DOI":"10.1021\/acs.analchem.5c07830","article-title":"Highly Sensitive Noninvasive Hemispherical Fiber Optic Photoacoustic Sensor Utilizing Dual Radial and Angular Resonant Modes for Simultaneous Multigas Detection","volume":"98","author":"Wu","year":"2026","journal-title":"Anal. Chem."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"139827","DOI":"10.1016\/j.snb.2026.139827","article-title":"Dual-Enhanced Fiber-Optic Photoacoustic Spectroscopy via Asymmetric Cavity Coupling and Cantilever Amplification for Sub-Ppb C2H2 Detection","volume":"458","author":"Wu","year":"2026","journal-title":"Sens. Actuators B Chem."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/16\/5291\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,8,23]],"date-time":"2026-08-23T04:10:36Z","timestamp":1787458236000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/26\/16\/5291"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,8,21]]},"references-count":25,"journal-issue":{"issue":"16","published-online":{"date-parts":[[2026,8]]}},"alternative-id":["s26165291"],"URL":"https:\/\/doi.org\/10.3390\/s26165291","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,8,21]]}}}