{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,28]],"date-time":"2026-02-28T04:29:56Z","timestamp":1772252996471,"version":"3.50.1"},"reference-count":40,"publisher":"MDPI AG","issue":"13","license":[{"start":{"date-parts":[[2025,6,21]],"date-time":"2025-06-21T00:00:00Z","timestamp":1750464000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"JSPS KAKENHI","award":["JP18H02016"],"award-info":[{"award-number":["JP18H02016"]}]},{"name":"JSPS KAKENHI","award":["JP24K01282"],"award-info":[{"award-number":["JP24K01282"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Nanomaterials"],"abstract":"<jats:p>Formaldehyde vapor (HCHO) is a harmful chemical substance and a potential air contaminant, with a permissible level in indoor spaces below 0.08 ppm (80 ppb). Thus, highly sensitive gas sensors for the continuous monitoring of HCHO are in demand. The electrical conductivity of semiconducting nanomaterials (e.g., single-walled carbon nanotubes (SWCNTs)) makes them sensitive to chemical substances adsorbed on their surfaces, and a variety of portable and highly sensitive chemiresistive gas sensors, including those capable of detecting HCHO, have been developed. However, when monitoring low levels of vapors (&lt;1 ppm) found in ambient air, most chemiresistive sensors face practical issues, including false responses to interfering effects (e.g., fluctuations in room temperature and humidity), baseline drift, and the need to apply a purge gas. Here, we report an actuator-driven, purge-free chemiresistive gas sensor that is capable of reliably detecting 0.05 ppm of HCHO in the air. This sensor is composed of an HCHO\u2192HCl converter (powdery hydroxylamine salt, HA), an HCl detector (a SWCNT-based chemiresistor), and an HCl blocker (a thin plastic plate). Upon exposure to HCHO, the HA emits HCl vapor, which diffuses onto the adjacent SWCNTs, increasing their electrical conductivity through p-doping. Meanwhile, inserting a plastic plate between HA and SWCNTs makes the conductivity of SWCNTs insensitive to HCHO. Thus, via periodic actuation (insertion and removal) of the plastic plate, HCHO can be detected reliably over a wide concentration range (0.05\u201315 ppm) with excellent selectivity over other volatile organic compounds. This actuator-driven system is beneficial because it does not require a purge gas for sensor recovery or baseline correction. Moreover, since the response to HCHO is synchronized with the actuation timing of the plate, even small (~0.8%) responses to 0.05 ppm of HCHO can be clearly separated from larger noise responses (&gt;1%) caused by interfering effects and baseline drift. We believe that this work provides substantial insights into the practical implementation of nanomaterial-based chemiresistive gas sensors.<\/jats:p>","DOI":"10.3390\/nano15130962","type":"journal-article","created":{"date-parts":[[2025,6,24]],"date-time":"2025-06-24T10:44:41Z","timestamp":1750761881000},"page":"962","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Actuator-Driven, Purge-Free Formaldehyde Gas Sensor Based on Single-Walled Carbon Nanotubes"],"prefix":"10.3390","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-6854-6032","authenticated-orcid":false,"given":"Shinsuke","family":"Ishihara","sequence":"first","affiliation":[{"name":"Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Mandeep K.","family":"Chahal","sequence":"additional","affiliation":[{"name":"Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japan"},{"name":"School of Chemistry and Forensic Science, University of Kent, Canterbury CT2 7NH, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8329-0634","authenticated-orcid":false,"given":"Jan","family":"Labuta","sequence":"additional","affiliation":[{"name":"Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japan"},{"name":"NMR Spectroscopy Group, Institute of Organic Chemistry and Biochemistry (IOCB), Czech Academy of Sciences (CAS), Flemingovo n\u00e1m. 2, 160 00 Prague, Czech Republic"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7547-7928","authenticated-orcid":false,"given":"Takeshi","family":"Tanaka","sequence":"additional","affiliation":[{"name":"Research Institute of Core Technology for Materials Innovation, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Ibaraki, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Hiromichi","family":"Kataura","sequence":"additional","affiliation":[{"name":"Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Ibaraki, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4229-5842","authenticated-orcid":false,"given":"Jonathan P.","family":"Hill","sequence":"additional","affiliation":[{"name":"Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8744-782X","authenticated-orcid":false,"given":"Takashi","family":"Nakanishi","sequence":"additional","affiliation":[{"name":"Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Ibaraki, Japan"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,6,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"2536","DOI":"10.1021\/cr800399g","article-title":"Formaldehyde in the Indoor Environment","volume":"100","author":"Salthammer","year":"2010","journal-title":"Chem. Rev."},{"key":"ref_2","unstructured":"WHO Regional Office for Europe (2000). Air Quality Guidelines for Europe, World Health Organization, Regional Office for Europe. [2nd ed.]."},{"key":"ref_3","unstructured":"(2025, April 11). Formaldehyde (Diffusive Samplers), Available online: https:\/\/www.osha.gov\/sites\/default\/files\/methods\/osha-1007.pdf."},{"key":"ref_4","unstructured":"(2025, April 11). Formaldehyde HCHO. Available online: https:\/\/www.gastec.co.jp\/files\/user\/asset\/pdf\/en\/detector_tube\/91LL.pdf."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"4468","DOI":"10.3390\/s130404468","article-title":"Formaldehyde Gas Sensors: A Review","volume":"13","author":"Chung","year":"2013","journal-title":"Sensors"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"6749","DOI":"10.1109\/JSEN.2015.2457931","article-title":"Thin-Film Sensors for Detection of Formaldehyde: A Review","volume":"15","author":"Chen","year":"2015","journal-title":"IEEE Sens. J."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"225","DOI":"10.1007\/s12274-018-2207-5","article-title":"Nanomaterials for Sensing of Formaldehyde in Air: Principles, Applications, and Performance Evaluation","volume":"12","author":"Kukkar","year":"2019","journal-title":"Nano Res."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"2423597","DOI":"10.1080\/14686996.2024.2423597","article-title":"Recent Progress on Polymeric Probes for Formaldehyde Sensing: A Comprehensive Review","volume":"25","author":"Roy","year":"2024","journal-title":"Sci. Technol. Adv. Mater."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"1","DOI":"10.3390\/chemosensors3010001","article-title":"First Fifty Years of Chemoresistive Gas Sensors","volume":"3","author":"Neri","year":"2015","journal-title":"Chemosensors"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"4571","DOI":"10.1021\/cr400659h","article-title":"Organic-Inorganic Hybrid Nanocomposite-Based Gas Sensors for Environmental Monitoring","volume":"115","author":"Kaushik","year":"2015","journal-title":"Chem. Rev."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"464","DOI":"10.1021\/acssensors.6b00250","article-title":"Wearable Chemical Sensors: Present Challenges and Future Prospects","volume":"1","author":"Bandodkar","year":"2016","journal-title":"ACS Sens."},{"key":"ref_12","first-page":"190192","article-title":"Advanced Soft Materials, Sensor Integrations, and Applications of Wearable Flexible Hybrid Electronics in Healthcare, Energy, and Environment","volume":"32","author":"Lim","year":"2020","journal-title":"Adv. Mater."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"887","DOI":"10.1038\/s41578-022-00460-x","article-title":"End-to-End Design of Wearable Sensors","volume":"7","author":"Ates","year":"2022","journal-title":"Nat. Rev. Mater."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"1902273","DOI":"10.1002\/adfm.201902273","article-title":"Recent Advances in Applications of Sorted Single-Walled Carbon Nanotubes","volume":"29","author":"Bati","year":"2019","journal-title":"Adv. Funct. Mater."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"149","DOI":"10.1038\/s44287-023-00011-8","article-title":"Chirality Engineering for Carbon Nanotube Electronics","volume":"1","author":"Tang","year":"2024","journal-title":"Nat. Rev. Electr. Eng."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"512","DOI":"10.1016\/j.snb.2007.07.059","article-title":"Preparation of Layered Organic-Inorganic Nanohybrid Thin Films of Molybdenum Trioxide with Polyaniline Derivatives for Aldehyde Gases Sensors of Several Tens ppb Level","volume":"128","author":"Itoh","year":"2008","journal-title":"Sens. Actuators B"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"364","DOI":"10.1016\/j.snb.2011.07.062","article-title":"High Sensitive and Selective Formaldehyde Sensors Based on Nanoparticle-assembled ZnO Micro-Octahedrons Synthesized by Homogeneous Precipitation Method","volume":"160","author":"Zhang","year":"2011","journal-title":"Sens. Actuators B"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"055502","DOI":"10.1088\/0957-4484\/22\/5\/055502","article-title":"A Carbon-Nanotube-Based Sensor Array for Formaldehyde Detection","volume":"22","author":"Lu","year":"2011","journal-title":"Nanotechnology"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"2892","DOI":"10.1039\/c0cc04978f","article-title":"Formaldehyde Gas Sensing Chip Based on Single-Walled Carbon Nanotubes and Thin Water Layer","volume":"47","author":"Kim","year":"2011","journal-title":"Chem. Commun."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"34","DOI":"10.1016\/j.snb.2011.12.112","article-title":"Multi-Wall Carbon Nanotube Gas Sensors Modified with Amino-Group to Detect Low Concentration of Formaldehyde","volume":"168","author":"Xie","year":"2012","journal-title":"Sens. Actuator B-Chem."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"370","DOI":"10.1016\/j.snb.2012.11.022","article-title":"Solid Organic Acid Tetrafluorohydroquinone Functionalized Signle-Walled Carbon Nanotube Chemiresistive Sensors for Highly Sensitive and Selective Formaldehyde Detection","volume":"177","author":"Shi","year":"2013","journal-title":"Sens. Actuator B Chem."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1405","DOI":"10.1021\/acssensors.7b00591","article-title":"Amperometric Detection of Sub-ppm Formaldehyde Using SWCNTs and Hydroxylamines: A Referenced Chemiresistive System","volume":"2","author":"Ishihara","year":"2017","journal-title":"ACS Sens."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"2611","DOI":"10.1021\/acssensors.0c01074","article-title":"Atomically Dispersed Au on In2O3 Nanosheets for Highly Sensitive and Selective Detection of Formaldehyde","volume":"5","author":"Gu","year":"2020","journal-title":"ACS Sens."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"2577","DOI":"10.1021\/acssensors.2c00589","article-title":"Ultrasensitive Formaldehyde Sensor Based on SnO2 with Rich Adsorbed Oxygen Derived from a Metal Organic Framework","volume":"7","author":"Deng","year":"2022","journal-title":"ACS Sens."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"790","DOI":"10.1039\/b515473c","article-title":"Chemical Vapor Detection Using Single-Walled Carbon Nanotubes","volume":"35","author":"Snow","year":"2006","journal-title":"Chem. Soc. Rev."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"6550","DOI":"10.1002\/anie.200704488","article-title":"Carbon Nanotube Gas and Vapor Sensors","volume":"47","author":"Kauffman","year":"2008","journal-title":"Angew. Chem. Int. Ed."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"599","DOI":"10.1021\/acs.chemrev.8b00340","article-title":"Carbon Nanotube Chemical Sensors","volume":"119","author":"Schroeder","year":"2019","journal-title":"Chem. Rev."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"1405","DOI":"10.1021\/acssensors.0c00194","article-title":"Cascade Reaction-Based Chemiresistive Array for Ethylene Sensing","volume":"5","author":"Ishihara","year":"2020","journal-title":"ACS Sens."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"73","DOI":"10.1038\/s43586-023-00255-6","article-title":"Chemiresistive Sensing with Functionalized Carbon Nanotubes","volume":"3","author":"Luo","year":"2023","journal-title":"Nat. Rev. Methods Primers"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"216049","DOI":"10.1016\/j.ccr.2024.216049","article-title":"Advances in Carbon Nanotube-Based Gas Sensors: Exploring the Path to the Future","volume":"518","author":"Luo","year":"2024","journal-title":"Coord. Chem. Rev."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"1266","DOI":"10.1002\/anie.201505308","article-title":"Nanowire Chemical\/Biological Sensors: Status and a Roadmap for the Future","volume":"55","author":"Fennell","year":"2016","journal-title":"Angew. Chem. Int. Ed."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"1585","DOI":"10.1021\/acssensors.2c02720","article-title":"Selective Detection of Toxic C1 Chemicals Using a Hydroxylamine-Based Chemiresistive Sensor Array","volume":"8","author":"Chahal","year":"2023","journal-title":"ACS Sens."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"12056","DOI":"10.1038\/ncomms12056","article-title":"Industrial-Scale Separation of High-Purity Single-Chirality Single-Wall Carbon Nanotubes for Biological Imaging","volume":"7","author":"Yomogida","year":"2016","journal-title":"Nat. Commun."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"8221","DOI":"10.1021\/jacs.6b03869","article-title":"Ultratrace Detection of Toxic Chemicals: Triggered Disassembly of Supramolecular Nanotube Wrappers","volume":"138","author":"Ishihara","year":"2016","journal-title":"J. Am. Chem. Soc."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"38062","DOI":"10.1021\/acsami.7b12992","article-title":"Metallic Versus Semiconducting SWCNT Chemiresistors: A Case for Separated SWCNTs Wrapped by a Metallosupramolecular Polymer","volume":"9","author":"Ishihara","year":"2017","journal-title":"ACS Appl. Mater. Interface"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"5472","DOI":"10.1039\/B311016H","article-title":"Doping of Single-Walled Carbon Nanotube Bundles by Br\u00f8nsted Acids","volume":"5","author":"Graupner","year":"2003","journal-title":"Phys. Chem. Chem. Phys."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"258","DOI":"10.1016\/j.cplett.2009.06.041","article-title":"Characterization of Acid-Treated Carbon Nanotube Thin Films by Means of Raman Spectroscopy and Field-Effect Response","volume":"476","author":"Zhang","year":"2009","journal-title":"Chem. Phys. Lett."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"548","DOI":"10.1186\/1556-276X-7-548","article-title":"Effect of Doping on Single-Walled Carbon Nanotubes Network of Different Metallicity","volume":"7","author":"Tey","year":"2012","journal-title":"Nanoscale Res. Lett."},{"key":"ref_39","first-page":"S49","article-title":"Limit of Blank, Limit of Detection and Limit of Quantitation","volume":"29","author":"Armbruster","year":"2008","journal-title":"Clin. Biochem. Rev."},{"key":"ref_40","unstructured":"McMurry, J. (1996). Organic Chemistry, Brooks\/Cole Publishing Company. [4th ed.]."}],"container-title":["Nanomaterials"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2079-4991\/15\/13\/962\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,9]],"date-time":"2025-10-09T17:56:20Z","timestamp":1760032580000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2079-4991\/15\/13\/962"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,6,21]]},"references-count":40,"journal-issue":{"issue":"13","published-online":{"date-parts":[[2025,7]]}},"alternative-id":["nano15130962"],"URL":"https:\/\/doi.org\/10.3390\/nano15130962","relation":{"has-preprint":[{"id-type":"doi","id":"10.26434\/chemrxiv-2025-jsswp","asserted-by":"object"}]},"ISSN":["2079-4991"],"issn-type":[{"value":"2079-4991","type":"electronic"}],"subject":[],"published":{"date-parts":[[2025,6,21]]}}}