{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,4]],"date-time":"2026-03-04T23:09:05Z","timestamp":1772665745145,"version":"3.50.1"},"reference-count":55,"publisher":"MDPI AG","issue":"11","license":[{"start":{"date-parts":[[2020,6,10]],"date-time":"2020-06-10T00:00:00Z","timestamp":1591747200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100000968","name":"American Heart Association","doi-asserted-by":"publisher","award":["19IPLOI34760577"],"award-info":[{"award-number":["19IPLOI34760577"]}],"id":[{"id":"10.13039\/100000968","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100008005","name":"Yonsei University College of Medicine","doi-asserted-by":"publisher","award":["6-2019-0169"],"award-info":[{"award-number":["6-2019-0169"]}],"id":[{"id":"10.13039\/501100008005","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Wireless, flexible, ion-selective electrodes (ISEs) are of great interest in the development of wearable health monitors and clinical systems. Existing film-based electrochemical sensors, however, still have practical limitations due to poor electrical contact and material\u2013interfacial leakage. Here, we introduce a wireless, flexible film-based system with a highly selective, stable, and reliable sodium sensor. A flexible and hydrophobic composite with carbon black and soft elastomer serves as an ion-to-electron transducer offering cost efficiency, design simplicity, and long-term stability. The sensor package demonstrates repeatable analysis of selective sodium detection in saliva with good sensitivity (56.1 mV\/decade), stability (0.53 mV\/h), and selectivity coefficient of sodium against potassium (\u22123.0). The film ISEs have an additional membrane coating that provides reinforced stability for the sensor upon mechanical bending. Collectively, the comprehensive study of materials, surface chemistry, and sensor design in this work shows the potential of the wireless flexible sensor system for low-profile wearable applications.<\/jats:p>","DOI":"10.3390\/s20113297","type":"journal-article","created":{"date-parts":[[2020,6,10]],"date-time":"2020-06-10T07:13:16Z","timestamp":1591773196000},"page":"3297","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":39,"title":["Wireless, Flexible, Ion-Selective Electrode System for Selective and Repeatable Detection of Sodium"],"prefix":"10.3390","volume":"20","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0828-2853","authenticated-orcid":false,"given":"Hyo-Ryoung","family":"Lim","sequence":"first","affiliation":[{"name":"George W. Woodruff School of Mechanical Engineering, Institute for Electronics and Nanotechnology, Georgia Institute of Technology, Atlanta, GA 30332, USA"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3892-7560","authenticated-orcid":false,"given":"Yun-Soung","family":"Kim","sequence":"additional","affiliation":[{"name":"George W. Woodruff School of Mechanical Engineering, Institute for Electronics and Nanotechnology, Georgia Institute of Technology, Atlanta, GA 30332, USA"}]},{"given":"Shinjae","family":"Kwon","sequence":"additional","affiliation":[{"name":"George W. Woodruff School of Mechanical Engineering, Institute for Electronics and Nanotechnology, Georgia Institute of Technology, Atlanta, GA 30332, USA"}]},{"given":"Musa","family":"Mahmood","sequence":"additional","affiliation":[{"name":"George W. Woodruff School of Mechanical Engineering, Institute for Electronics and Nanotechnology, Georgia Institute of Technology, Atlanta, GA 30332, USA"}]},{"given":"Young-Tae","family":"Kwon","sequence":"additional","affiliation":[{"name":"George W. Woodruff School of Mechanical Engineering, Institute for Electronics and Nanotechnology, Georgia Institute of Technology, Atlanta, GA 30332, USA"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8452-2225","authenticated-orcid":false,"given":"Yongkuk","family":"Lee","sequence":"additional","affiliation":[{"name":"Department of Biomedical Engineering, Wichita State University, Wichita, KS 67260, USA"}]},{"given":"Soon Min","family":"Lee","sequence":"additional","affiliation":[{"name":"Department of Pediatrics, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul 06273, Korea"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5526-3882","authenticated-orcid":false,"given":"Woon-Hong","family":"Yeo","sequence":"additional","affiliation":[{"name":"George W. Woodruff School of Mechanical Engineering, Institute for Electronics and Nanotechnology, Georgia Institute of Technology, Atlanta, GA 30332, USA"},{"name":"Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University School of Medicine, Atlanta, GA 30322, USA"},{"name":"Parker H. Petit Institute for Bioengineering and Biosciences, Institute for Materials, Neural Engineering Center, Institute for Robotics and Intelligent Machines, Georgia Institute of Technology, Atlanta, GA 30332, USA"}]}],"member":"1968","published-online":{"date-parts":[[2020,6,10]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"64","DOI":"10.1039\/C5AY02254A","article-title":"An integrated sensing and wireless communications platform for sensing sodium in sweat","volume":"8","author":"Matzeu","year":"2016","journal-title":"Anal. Methods"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"6240","DOI":"10.1021\/acs.analchem.8b00850","article-title":"Open-source potentiostat for wireless electrochemical detection with smartphones","volume":"90","author":"Ainla","year":"2018","journal-title":"Anal. Chem."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"5377","DOI":"10.1073\/pnas.1719573115","article-title":"Wireless, intraoral hybrid electronics for real-time quantification of sodium intake toward hypertension management","volume":"115","author":"Lee","year":"2018","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"523","DOI":"10.2170\/jjphysiol.13.523","article-title":"Reflection of salt concentrations of blood upon those of saliva","volume":"13","author":"Yoshimura","year":"1963","journal-title":"Jpn. J. Physiol."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"3152146","DOI":"10.1155\/2018\/3152146","article-title":"Differential associations for salivary sodium, potassium, calcium, and phosphate levels with carotid intima media thickness, heart rate, and arterial stiffness","volume":"2018","author":"Labat","year":"2018","journal-title":"Dis. Markers"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"443","DOI":"10.1016\/j.jped.2018.04.005","article-title":"Chloride and sodium ion concentrations in saliva and sweat as a method to diagnose cystic fibrosis","volume":"95","author":"Marson","year":"2019","journal-title":"J. Pediatr."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"131","DOI":"10.1016\/j.snb.2014.11.107","article-title":"Solid contact cadmium ion-selective electrode based on ionic liquid and carbon nanotubes","volume":"209","author":"Wardak","year":"2015","journal-title":"Sens. Actuators B Chem."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"8810","DOI":"10.1021\/ac202070r","article-title":"Potentiometric strip cell based on carbon nanotubes as transducer layer: Toward low-cost decentralized measurements","volume":"83","author":"Crespo","year":"2011","journal-title":"Anal. Chem."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"7111","DOI":"10.1021\/ac501633r","article-title":"Ion-selective electrodes with colloid-imprinted mesoporous carbon as solid contact","volume":"86","author":"Hu","year":"2014","journal-title":"Anal. Chem."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1800778","DOI":"10.1002\/aelm.201800778","article-title":"3D printed disposable wireless ion sensors with biocompatible cellulose composites","volume":"5","author":"Kim","year":"2019","journal-title":"Adv. Electron. Mater."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"3140","DOI":"10.1021\/acs.est.8b05928","article-title":"Real-time in situ monitoring of nitrogen dynamics in wastewater treatment processes using wireless, solid-state, and ion-selective membrane sensors","volume":"53","author":"Huang","year":"2019","journal-title":"Environ. Sci. Technol."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"10224","DOI":"10.1021\/acs.analchem.7b01560","article-title":"Wearable sweatband sensor platform based on gold nanodendrite array as efficient solid contact of ion-selective electrode","volume":"89","author":"Wang","year":"2017","journal-title":"Anal. Chem."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"9111","DOI":"10.1021\/acs.analchem.9b01587","article-title":"Potential reproducibility of potassium-selective electrodes having perfluorinated alkanoate side-chain functionalized poly (3, 4-ethylenedioxytiophene) as hydrophobic solid contact","volume":"91","author":"Papp","year":"2019","journal-title":"Anal. Chem."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"9010","DOI":"10.1021\/acs.analchem.9b01286","article-title":"Multiwalled carbon nanotubes\u2013poly(3-octylthiophene-2,5-diyl) nanocomposite transducer for ion-selective electrodes: Raman spectroscopy insight into the transducer\/membrane interface","volume":"91","author":"Jaworska","year":"2019","journal-title":"Anal. Chem."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"624","DOI":"10.1016\/j.snb.2015.10.054","article-title":"Few-layer graphene and polyaniline composite as ion-to-electron transducer in silicone rubber solid-contact ion-selective electrodes","volume":"224","author":"Boeva","year":"2016","journal-title":"Sens. Actuators B Chem."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"172","DOI":"10.1016\/j.aca.2007.08.038","article-title":"Use of organofunctionalized nanoporous silica gel to improve the lifetime of carbon paste electrode for determination of copper(II) ions","volume":"601","author":"Javanbakht","year":"2007","journal-title":"Anal. Chim. Acta"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"7107","DOI":"10.1021\/acs.analchem.7b01027","article-title":"Introducing cobalt(II) porphyrin\/cobalt(III) corrole containing transducers for improved potential reproducibility and performance of all-solid-state ion-selective electrodes","volume":"89","author":"Jaworska","year":"2017","journal-title":"Anal. Chem."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"402","DOI":"10.1016\/j.jhazmat.2010.07.039","article-title":"Multi-walled carbon nanotubes-ionic liquid-carbon paste electrode as a super selectivity sensor: Application to potentiometric monitoring of mercury ion(II)","volume":"183","author":"Khani","year":"2010","journal-title":"J. Hazard. Mater."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"291","DOI":"10.1016\/j.aca.2014.10.033","article-title":"A simple approach for fabricating solid-contact ion-selective electrodes using nanomaterials as transducers","volume":"853","author":"Liang","year":"2015","journal-title":"Anal. Chim. Acta"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"21","DOI":"10.1016\/j.jelechem.2014.12.038","article-title":"Highly hydrophobic solid contact based on graphene-hybrid nanocomposites for all solid state potentiometric sensors with well-formulated phase boundary potentials","volume":"740","author":"Sun","year":"2015","journal-title":"J. Electroanal. Chem."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1890","DOI":"10.1080\/00032719.2017.1395035","article-title":"Electrochemical determination of copper(II) in water samples using a novel ion-selective electrode based on a graphite oxide\u2013imprinted polymer composite","volume":"51","author":"Topcu","year":"2018","journal-title":"Anal. Lett."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"166","DOI":"10.1016\/j.snb.2010.04.041","article-title":"Single-piece solid-contact ion-selective electrodes with polymer\u2013carbon nanotube composites","volume":"148","author":"Zhu","year":"2010","journal-title":"Sens. Actuators B Chem."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1684","DOI":"10.1016\/j.elecom.2009.06.025","article-title":"Preparation of all solid-state potentiometric ion sensors with polymer-CNT composites","volume":"11","author":"Zhu","year":"2009","journal-title":"Electrochem. Commun."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"3473","DOI":"10.1021\/ac203480z","article-title":"Application of electrochemically reduced graphene oxide on screen-printed ion-selective electrode","volume":"84","author":"Ping","year":"2012","journal-title":"Anal. Chem."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"375501","DOI":"10.1088\/0957-4484\/26\/37\/375501","article-title":"Ultra-stretchable and skin-mountable strain sensors using carbon nanotubes\u2013Ecoflex nanocomposites","volume":"26","author":"Amjadi","year":"2015","journal-title":"Nanotechnology"},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Cholleti, E.R., Stringer, J., Assadian, M., Battmann, V., Bowen, C., and Aw, K. (2018). Highly stretchable capacitive sensor with printed carbon black electrodes on barium titanate elastomer composite. Sensor, 19.","DOI":"10.3390\/s19010042"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"514","DOI":"10.1016\/j.sna.2016.06.037","article-title":"Fabrication and characterisation of highly stretchable elastomeric strain sensors for prosthetic hand applications","volume":"247","author":"Mutlu","year":"2016","journal-title":"Sens. Actuators A Phys."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"1700284","DOI":"10.1002\/admt.201700284","article-title":"Ultrastretchable strain sensors using carbon black-filled elastomer composites and comparison of capacitive versus resistive sensors","volume":"3","author":"Shintake","year":"2018","journal-title":"Adv. Mater. Technol."},{"key":"ref_29","doi-asserted-by":"crossref","unstructured":"Zhu, Y., Assadian, M., Ramezani, M., and Aw, K.C. (2018). Printing of soft stretch sensor from carbon black composites. Proceedings, 2.","DOI":"10.3390\/proceedings2130732"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"414","DOI":"10.3934\/matersci.2015.4.414","article-title":"Vapor phase polymerization of PEDOT on silicone rubber as flexible large strain sensor","volume":"2","author":"Giffney","year":"2015","journal-title":"Aims Mater. Sci."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"2819","DOI":"10.1039\/C5LC00285K","article-title":"Instantaneous room temperature bonding of a wide range of non-silicon substrates with poly(dimethylsiloxane) (PDMS) elastomer mediated by a mercaptosilane","volume":"15","author":"Wu","year":"2015","journal-title":"Lab. A Chip"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"1618","DOI":"10.1021\/ac991167h","article-title":"Cationic or anionic sites? Selectivity optimization of ion-selective electrodes based on charged ionophores","volume":"72","author":"Amemiya","year":"2000","journal-title":"Anal. Chem."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"eaay1729","DOI":"10.1126\/sciadv.aay1729","article-title":"Soft, wireless periocular wearable electronics for real-time detection of eye vergence in a virtual reality toward mobile eye therapies","volume":"6","author":"Mishra","year":"2020","journal-title":"Sci. Adv."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"412","DOI":"10.1038\/s42256-019-0091-7","article-title":"Fully portable and wireless universal brain\u2013machine interfaces enabled by flexible scalp electronics and deep learning algorithm","volume":"1","author":"Mahmood","year":"2019","journal-title":"Nat. Mach. Intell."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"72","DOI":"10.1016\/j.aca.2014.02.028","article-title":"A reference electrode based on polyvinyl butyral (PVB) polymer for decentralized chemical measurements","volume":"821","author":"Guinovart","year":"2014","journal-title":"Anal. Chim. Acta"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"261","DOI":"10.1016\/S0377-1237(17)31082-1","article-title":"Relative changes in salivary sodium and potassium in relation to exposure to high G stress","volume":"50","author":"Singh","year":"1994","journal-title":"Med. J. Armed Forces India"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"246","DOI":"10.1172\/JCI103077","article-title":"Physiological and pharmacological regulation of human salivary electrolyte concentrations; with a discussion of electrolyte concentrations of some other exocrine secretions","volume":"34","author":"White","year":"1955","journal-title":"J. Clin. Investig."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"4932","DOI":"10.1021\/ac990497z","article-title":"Potential stability of all-solid-state ion-selective electrodes using conducting polymers as ion-to-electron transducers","volume":"71","author":"Bobacka","year":"1999","journal-title":"Anal. Chem."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"4621","DOI":"10.1021\/ac070132b","article-title":"Ion-selective electrodes with three-dimensionally ordered macroporous carbon as the solid contact","volume":"79","author":"Lai","year":"2007","journal-title":"Anal. Chem."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"448","DOI":"10.1016\/S1452-3981(23)15297-7","article-title":"\u03b2-Cyclodextrin-based potentiometric sensors for flow-injection determination of acetylcholines","volume":"5","author":"Khaled","year":"2010","journal-title":"Int. J. Electrochem. Sci."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"2400","DOI":"10.1016\/S1452-3981(23)04855-1","article-title":"Novel pioglitazone nanomaterial based screen printed sensors","volume":"10","author":"Kamel","year":"2015","journal-title":"Int. J. Electrochem. Sci."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"89","DOI":"10.1016\/j.snb.2018.05.018","article-title":"Multiplexed analysis of molecular and elemental ions using nanowire transistor sensors","volume":"270","author":"Chen","year":"2018","journal-title":"Sens. Actuators B Chem."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"323","DOI":"10.1007\/s10847-016-0661-9","article-title":"New bis(azobenzocrown)s with dodecylmethylmalonyl linkers as ionophores for sodium selective potentiometric sensors","volume":"86","author":"Luboch","year":"2016","journal-title":"J. Incl. Phenom. Macrocycl. Chem."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"2861","DOI":"10.1016\/j.snb.2017.09.104","article-title":"Miniaturized multiparametric flexible platform for the simultaneous monitoring of ionic: Application in real urine","volume":"255","author":"Moya","year":"2018","journal-title":"Sens. Actuators B Chem."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"1718","DOI":"10.1021\/ac503521t","article-title":"Application of nanostructured TCNQ to potentiometric ion-selective K+ and Na+ electrodes","volume":"87","author":"Piech","year":"2015","journal-title":"Anal. Chem."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"336","DOI":"10.1016\/j.bios.2017.11.003","article-title":"New sensor based on membranes with magnetic nano-inclusions for early diagnosis in periodontal disease","volume":"102","author":"Totu","year":"2018","journal-title":"Biosens. Bioelectron."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"1851","DOI":"10.1351\/pac200072101851","article-title":"Potentiometric selectivity coefficients of ion-selective electrodes. Part I. Inorganic cations (technical report)","volume":"72","author":"Umezawa","year":"2000","journal-title":"Pure Appl. Chem."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"6572381","DOI":"10.1155\/2018\/6572381","article-title":"A review of selected studies that determine the physical and chemical properties of saliva in the field of dental treatment","volume":"2018","author":"Kubala","year":"2018","journal-title":"Biomed. Res. Int."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"9223","DOI":"10.1021\/acsnano.8b03962","article-title":"Electrochemistry on stretchable nanocomposite electrodes: Dependence on strain","volume":"12","author":"Lopez","year":"2018","journal-title":"ACS Nano"},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"624","DOI":"10.1016\/j.nanoen.2019.01.084","article-title":"Wearable sweat monitoring system with integrated micro-supercapacitors","volume":"58","author":"Lu","year":"2019","journal-title":"Nano Energy"},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"35169","DOI":"10.1021\/acsami.7b07346","article-title":"Carbon nanotube-based ion selective sensors for wearable applications","volume":"9","author":"Roy","year":"2017","journal-title":"ACS Appl. Mater. Interfaces"},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"15421","DOI":"10.1021\/acsomega.9b01464","article-title":"Thin and flexible ion sensors based on polyelectrolyte multilayers assembled onto the carbon adhesive tape","volume":"4","author":"Stekolshchikova","year":"2019","journal-title":"ACS Omega"},{"key":"ref_53","doi-asserted-by":"crossref","first-page":"106553","DOI":"10.1016\/j.elecom.2019.106553","article-title":"A multichannel electrochemical all-solid-state wearable potentiometric sensor for real-time sweat ion monitoring","volume":"107","author":"An","year":"2019","journal-title":"Electrochem. Commun."},{"key":"ref_54","doi-asserted-by":"crossref","first-page":"120869","DOI":"10.1016\/j.talanta.2020.120869","article-title":"Highly stretchable potentiometric ion sensor based on surface strain redistributed fiber for sweat monitoring","volume":"214","author":"Wang","year":"2020","journal-title":"Talanta"},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"1267","DOI":"10.1002\/elan.201600070","article-title":"Wearable potentiometric sensors based on commercial carbon fibres for monitoring sodium in sweat","volume":"28","author":"Parrilla","year":"2016","journal-title":"Electroanalysis"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/20\/11\/3297\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T09:37:23Z","timestamp":1760175443000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/20\/11\/3297"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,6,10]]},"references-count":55,"journal-issue":{"issue":"11","published-online":{"date-parts":[[2020,6]]}},"alternative-id":["s20113297"],"URL":"https:\/\/doi.org\/10.3390\/s20113297","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2020,6,10]]}}}