{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,22]],"date-time":"2026-03-22T04:39:59Z","timestamp":1774154399458,"version":"3.50.1"},"reference-count":40,"publisher":"MDPI AG","issue":"14","license":[{"start":{"date-parts":[[2025,7,9]],"date-time":"2025-07-09T00:00:00Z","timestamp":1752019200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100006260","name":"Technion - Israel Institute of Technology","doi-asserted-by":"publisher","award":["Internal Fund"],"award-info":[{"award-number":["Internal Fund"]}],"id":[{"id":"10.13039\/501100006260","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Benzene, toluene, ethylbenzene, and xylene (BTEX) are widespread volatile organic compounds commonly present in fuels and various industrial materials. Their release into the atmosphere significantly contributes to air pollution, prompting strict regulatory concentration limits in ambient air. In this work, we introduce Multiphoton Electron Extraction Spectroscopy (MEES) as an innovative technique for the sensitive, selective, and online detection and quantitation of BTEX compounds under ambient conditions. MEES employs tunable UV laser pulses to induce the resonant ionization of target molecules under a high electrical field, with subsequent measurement of the generated photocurrent. We now demonstrate the method\u2019s ability to detect BTEX in ambient air, at part-per-trillion (ppt) concentration range, providing distinct spectral signatures for each compound, including individual xylene isomers. The technique represents a significant advancement in BTEX monitoring, with potential applications in environmental sensing and industrial air quality control.<\/jats:p>","DOI":"10.3390\/s25144268","type":"journal-article","created":{"date-parts":[[2025,7,11]],"date-time":"2025-07-11T10:26:53Z","timestamp":1752229613000},"page":"4268","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["High Sensitivity Online Sensor for BTEX in Ambient Air Based on Multiphoton Electron Extraction Spectroscopy"],"prefix":"10.3390","volume":"25","author":[{"ORCID":"https:\/\/orcid.org\/0009-0008-1045-7019","authenticated-orcid":false,"given":"Uriah H.","family":"Sharon","sequence":"first","affiliation":[{"name":"Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Lea","family":"Birkan","sequence":"additional","affiliation":[{"name":"Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Valery","family":"Bulatov","sequence":"additional","affiliation":[{"name":"Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7277-3964","authenticated-orcid":false,"given":"Roman","family":"Schuetz","sequence":"additional","affiliation":[{"name":"Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8266-9749","authenticated-orcid":false,"given":"Tikhon","family":"Filippov","sequence":"additional","affiliation":[{"name":"Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Israel","family":"Schechter","sequence":"additional","affiliation":[{"name":"Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,7,9]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"David, E., and Niculescu, V.C. (2021). Volatile Organic Compounds (VOCs) as Environmental Pollutants: Occurrence and Mitigation Using Nanomaterials. Int. J. Environ. Res. Public Health, 18.","DOI":"10.3390\/ijerph182413147"},{"key":"ref_2","unstructured":"(2025, June 01). Initial List of Hazardous Air Pollutants with Modifications|US EPA, Available online: https:\/\/www.epa.gov\/haps\/initial-list-hazardous-air-pollutants-modifications."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"133","DOI":"10.1016\/j.ecoenv.2018.02.065","article-title":"Characteristics and Health Effects of BTEX in a Hot Spot for Urban Pollution","volume":"155","author":"Dehghani","year":"2018","journal-title":"Ecotoxicol. Environ. Saf."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"134825","DOI":"10.1016\/j.cej.2022.134825","article-title":"BTEX in the Environment: An Update on Sources, Fate, Distribution, Pretreatment, Analysis, and Removal Techniques","volume":"435","author":"Yu","year":"2022","journal-title":"Chem. Eng. J."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"105825","DOI":"10.1016\/j.tiv.2024.105825","article-title":"Risk Assessment of Benzene, Toluene, Ethyl Benzene, and Xylene (BTEX) in the Atmospheric Air around the World: A Review","volume":"98","author":"Zahed","year":"2024","journal-title":"Toxicol. Vitr."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"137986","DOI":"10.1016\/j.jhazmat.2025.137986","article-title":"Exposure and Health Risks of Benzene from Combustion by Gas Stoves: A Modelling Approach in U.S. Homes","volume":"492","author":"Garg","year":"2025","journal-title":"J. Hazard. Mater."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Ghasemi, R., Saranjam, B., Zarei, A., Babaei, A., Ghaffari, H.R., and Fazlzadeh, M. (2025). Assessment of Health Risks of University Professors through Exposure to BTEX Compounds from White Board Markers. Sci. Rep., 15.","DOI":"10.1038\/s41598-025-92336-7"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"5261","DOI":"10.1021\/es505316f","article-title":"New Look at BTEX: Are Ambient Levels a Problem","volume":"49","author":"Bolden","year":"2015","journal-title":"Environ. Sci. Technol."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"4715","DOI":"10.5194\/bg-19-4715-2022","article-title":"Reviews and Syntheses: VOC Emissions from Soil Cover in Boreal and Temperate Natural Ecosystems of the Northern Hemisphere","volume":"19","author":"Isidorov","year":"2022","journal-title":"Biogeosciences"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"83","DOI":"10.1016\/j.taap.2014.02.012","article-title":"Current Understandings and Perspectives on Non-Cancer Health Effects of Benzene: A Global Concern","volume":"276","author":"Bahadar","year":"2014","journal-title":"Toxicol. Appl. Pharmacol."},{"key":"ref_11","unstructured":"(2025, June 01). BS EN 14662-3:2015 Ambient Air; Standard Method for the Measurement of Benzene Concentrations Automated Pumped Sampling with in Situ Gas Chromatography. Available online: https:\/\/www.en-standard.eu\/bs-en-14662-3-2015-ambient-air-standard-method-for-the-measurement-of-benzene-concentrations-automated-pumped-sampling-with-in-situ-gas-chromatography\/."},{"key":"ref_12","unstructured":"Almog, S., Trachtman, A., Nezer, S., and Crescenti, E. (2025, June 18). Report of the Committee for Determining Environmental Reference Values for Chemical Pollutants in the Air, Available online: https:\/\/www.gov.il\/BlobFolder\/reports\/chemical-pollutants\/he\/air_quality_chemical-pollutants.pdf."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"100146","DOI":"10.1016\/j.eehl.2025.100146","article-title":"Long-Term Exposure to Low-Level Ambient BTEX and Site-Specific Cancer Risk: A National Cohort Study in the UK Biobank","volume":"4","author":"Yu","year":"2025","journal-title":"Eco-Environ. Health"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"e02918","DOI":"10.1016\/j.heliyon.2019.e02918","article-title":"Analysis of Benzene Air Quality Standards, Monitoring Methods and Concentrations in Indoor and Outdoor Environment","volume":"5","author":"Sekar","year":"2019","journal-title":"Heliyon"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"625","DOI":"10.5194\/acp-25-625-2025","article-title":"Measurement Report: Exploring the Variations in Ambient BTEX in Urban Europe and Their Environmental Health Implications","volume":"25","author":"Liu","year":"2025","journal-title":"Atmos. Chem. Phys."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"446","DOI":"10.1016\/j.snb.2013.03.010","article-title":"Portable, Miniature, Fast and High Sensitive Real-Time Analyzers: BTEX Detection","volume":"182","author":"Allouch","year":"2013","journal-title":"Sens. Actuators B Chem."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"100210","DOI":"10.1016\/j.snr.2024.100210","article-title":"Critical Review of Potential Technologies for a Weara-ble Benzene Sensor System","volume":"8","author":"Dunker","year":"2024","journal-title":"Sensors Actuators Rep."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Ragbir, P., Kaduwela, A., Passovoy, D., Amin, P., Ye, S., Wallis, C., Alaimo, C., Young, T., and Kong, Z. (2023). UAV-Based Wildland Fire Air Toxics Data Collection and Analysis. Sensors, 23.","DOI":"10.3390\/s23073561"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"2892","DOI":"10.1364\/AO.516293","article-title":"Highly Sensitive and Selective Laser-Based BTEX Sensor for Occupational and Environmental Monitoring","volume":"63","author":"Mhanna","year":"2024","journal-title":"Appl Opt."},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Khan, S., Newport, D., and Le Calv\u00e9, S. (2020). Low-Volume PEEK Gas Cell for BTEX Detection Using Portable Deep-UV Ab-sorption Spectrophotometry. Acta Part A: Mol. Biomol. Spectrosc., 243.","DOI":"10.1016\/j.saa.2020.118727"},{"key":"ref_21","doi-asserted-by":"crossref","unstructured":"Filippov, T., Vervitski, E., Kofler, H., Birkan, L., Levy, S., Zimmerman, S., Bulatov, V., Schechter, I., and Schuetz, R. (2024). Sub-PPB Detection with Gas-Phase Multiphoton Electron Extraction Spectroscopy under Ambient Conditions. Sensors, 24.","DOI":"10.3390\/s24072040"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"3451","DOI":"10.1039\/D3CP05559K","article-title":"On the Multiphoton Ionisation Photoelectron Spectra of Phenol","volume":"26","author":"Dey","year":"2024","journal-title":"Phys. Chem. Chem. Phys."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"072001","DOI":"10.1088\/1361-6455\/adbfea","article-title":"Resonant Photoionization and Time Delay","volume":"58","author":"Kheifets","year":"2025","journal-title":"J. Phys. B At. Mol. Opt. Phys."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"462023","DOI":"10.1016\/j.chroma.2021.462023","article-title":"Femtosecond Ionization Mass Spectrometry for Chromatographic Detection","volume":"1642","author":"Imasaka","year":"2021","journal-title":"J. Chromatogr. A"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"3454","DOI":"10.1021\/ac100539x","article-title":"Multiphoton Ionization Spectroscopy as a Diagnostic Technique of Surfaces Under Ambient Conditions","volume":"82","author":"Chen","year":"2010","journal-title":"Anal. Chem."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"329","DOI":"10.1016\/j.optmat.2011.05.016","article-title":"Spectral Characterization of Surfaces Using Laser Multi-Photon Ionization","volume":"34","author":"Vinerot","year":"2011","journal-title":"Opt. Mater."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"676","DOI":"10.1021\/acs.analchem.4c05040","article-title":"Atmospheric Pressure Laser Ionization Mass Spectrometry with Tunable UV Wavelength Utilizing an Optical Parametric Oscillator","volume":"97","author":"Etscheidt","year":"2025","journal-title":"Anal. Chem."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"235","DOI":"10.1016\/j.talanta.2016.04.027","article-title":"Detection and Mapping of Trace Explosives on Surfaces under Ambient Conditions Using Multiphoton Electron Extraction Spectroscopy (MEES)","volume":"155","author":"Tang","year":"2016","journal-title":"Talanta"},{"key":"ref_29","doi-asserted-by":"crossref","unstructured":"Fisher, D., Bulatov, V., and Schechter, I. (2021). Authentication and Testing of Banknotes Using Laser Multiphoton Electron Extraction Spectroscopy (MEES). Appl. Sci., 11.","DOI":"10.3390\/app112110465"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"100094","DOI":"10.1016\/j.talo.2022.100094","article-title":"Application of Multiphoton Electron Extraction Spectroscopy (MEES) to Printed Document Forensics","volume":"5","author":"Fisher","year":"2022","journal-title":"Talanta Open"},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"8037","DOI":"10.1007\/s00216-016-9904-2","article-title":"Multiphoton Electron Extraction Spectroscopy and Its Comparison with Other Spectroscopies for Direct Detection of Solids under Ambient Conditions","volume":"408","author":"Tang","year":"2016","journal-title":"Anal. Bioanal. Chem."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"1369","DOI":"10.1039\/b508536e","article-title":"Thermogravimetric Calibration of Permeation Tubes Used for the Preparation of Gas Standards for Air Pollution Analysis","volume":"130","author":"Tumbiolo","year":"2005","journal-title":"Analyst"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"4286","DOI":"10.1021\/acs.analchem.1c04940","article-title":"A Demonstration of Broadband Cavity-Enhanced Absorption Spectroscopy at Deep-Ultraviolet Wavelengths: Application to Sensitive Real-Time Detection of the Aromatic Pollutants Benzene, Toluene, and Xylene","volume":"94","author":"Wang","year":"2022","journal-title":"Anal. Chem."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"525","DOI":"10.1016\/S1352-2310(98)00289-1","article-title":"Gas-Phase Absorption Cross Sections of 24 Monocyclic Aromatic Hydrocarbons in the UV and IR Spectral Ranges","volume":"33","author":"Etzkorn","year":"1999","journal-title":"Atmos. Environ."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"766","DOI":"10.1016\/j.jqsrt.2008.11.014","article-title":"UV Fourier Transform Absorption Cross Sections of Benzene, Toluene, Meta-, Ortho-, and Para-Xylene","volume":"110","author":"Fally","year":"2009","journal-title":"J. Quant. Spectrosc. Radiat. Transf."},{"key":"ref_36","unstructured":"Keller-Rudek, H., Moortgat, G.K., Sander, R., and S\u00f6rensen, R. (2025, July 06). The MPI-Mainz UV\/VIS Spectral Atlas of Gaseous Molecules of Atmospheric Interest. Available online: https:\/\/uv-vis-spectral-atlas-mainz.org\/uvvis\/cross_sections\/Aromatic%20compounds\/Alkyl-,vinylbenzenes\/."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"2940","DOI":"10.1039\/b400997e","article-title":"Absorption and Fluorescence of Toluene Vapor at Elevated Temperatures","volume":"6","author":"Koban","year":"2004","journal-title":"Phys. Chem. Chem. Phys."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"511","DOI":"10.1063\/1.1724185","article-title":"The Near Ultraviolet Absorption Spectrum of Toluene Vapor","volume":"14","author":"Ginsburg","year":"1946","journal-title":"J. Chem. Phys."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"1705","DOI":"10.1063\/1.1670297","article-title":"Electronic Energy Relaxation in Toluene Vapor","volume":"49","author":"Burton","year":"1968","journal-title":"J. Chem. Phys."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"368","DOI":"10.1007\/BF00474603","article-title":"Contribution to the statistical definition of the limits of reliable assay measurement","volume":"323","author":"Heise","year":"1986","journal-title":"Z. Anal. Chem."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/25\/14\/4268\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,9]],"date-time":"2025-10-09T18:07:10Z","timestamp":1760033230000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/25\/14\/4268"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,7,9]]},"references-count":40,"journal-issue":{"issue":"14","published-online":{"date-parts":[[2025,7]]}},"alternative-id":["s25144268"],"URL":"https:\/\/doi.org\/10.3390\/s25144268","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2025,7,9]]}}}