{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,11]],"date-time":"2026-02-11T19:30:45Z","timestamp":1770838245073,"version":"3.50.1"},"reference-count":48,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2024,1,10]],"date-time":"2024-01-10T00:00:00Z","timestamp":1704844800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100000781","name":"European Research Council","doi-asserted-by":"publisher","award":["816006"],"award-info":[{"award-number":["816006"]}],"id":[{"id":"10.13039\/501100000781","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100000781","name":"European Research Council","doi-asserted-by":"publisher","award":["EXC-2193\/1\u2013390951807"],"award-info":[{"award-number":["EXC-2193\/1\u2013390951807"]}],"id":[{"id":"10.13039\/501100000781","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Carl Zeiss Foundation","award":["816006"],"award-info":[{"award-number":["816006"]}]},{"name":"Carl Zeiss Foundation","award":["EXC-2193\/1\u2013390951807"],"award-info":[{"award-number":["EXC-2193\/1\u2013390951807"]}]},{"name":"Deutsche Forschungsgemeinschaft (DFG German Research Foundation)","award":["816006"],"award-info":[{"award-number":["816006"]}]},{"name":"Deutsche Forschungsgemeinschaft (DFG German Research Foundation)","award":["EXC-2193\/1\u2013390951807"],"award-info":[{"award-number":["EXC-2193\/1\u2013390951807"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Gallium liquid metals (LMs) like Galinstan and eutectic Gallium-Indium (EGaIn) have seen increasing applications in heavy metal ion (HMI) sensing, because of their ability to amalgamate with HMIs like lead, their high hydrogen potential, and their stable electrochemical window. Furthermore, coating LM droplets with nanopowders of tungsten oxide (WO) has shown enhancement in HMI sensing owing to intense electrical fields at the nanopowder-liquid\u2013metal interface. However, most LM HMI sensors are droplet based, which show limitations in scalability and the homogeneity of the surface. A scalable approach that can be extended to LM electrodes is therefore highly desirable. In this work, we present, for the first time, WO-Galinstan HMI sensors fabricated via photolithography of a negative cavity, Galinstan brushing inside the cavity, lift-off, and galvanic replacement (GR) in a tungsten salt solution. Successful GR of Galinstan was verified using optical microscopy, SEM, EDX, XPS, and surface roughness measurements of the Galinstan electrodes. The fabricated WO-Galinstan electrodes demonstrated enhanced sensitivity in comparison with electrodes structured from pure Galinstan and detected lead at concentrations down to 0.1 mmol\u00b7L\u22121. This work paves the way for a new class of HMI sensors using GR of WO-Galinstan electrodes, with applications in microfluidics and MEMS for a toxic-free environment.<\/jats:p>","DOI":"10.3390\/s24020416","type":"journal-article","created":{"date-parts":[[2024,1,10]],"date-time":"2024-01-10T07:50:48Z","timestamp":1704873048000},"page":"416","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Tungsten Oxide Coated Liquid Metal Electrodes via Galvanic Replacement as Heavy Metal Ion Sensors"],"prefix":"10.3390","volume":"24","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9295-0606","authenticated-orcid":false,"given":"Sagar","family":"Bhagwat","sequence":"first","affiliation":[{"name":"Laboratory of Process Technology, NeptunLab, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-K\u00f6hler-Allee 103,  79110 Freiburg im Breisgau, Germany"}]},{"given":"Leonhard","family":"Hambitzer","sequence":"additional","affiliation":[{"name":"Laboratory of Process Technology, NeptunLab, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-K\u00f6hler-Allee 103,  79110 Freiburg im Breisgau, Germany"}]},{"given":"Richard","family":"Prediger","sequence":"additional","affiliation":[{"name":"Laboratory of Process Technology, NeptunLab, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-K\u00f6hler-Allee 103,  79110 Freiburg im Breisgau, Germany"}]},{"given":"Pang","family":"Zhu","sequence":"additional","affiliation":[{"name":"Laboratory of Process Technology, NeptunLab, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-K\u00f6hler-Allee 103,  79110 Freiburg im Breisgau, Germany"}]},{"ORCID":"https:\/\/orcid.org\/0009-0009-1518-5582","authenticated-orcid":false,"given":"Ahmed","family":"Hamza","sequence":"additional","affiliation":[{"name":"Laboratory of Process Technology, NeptunLab, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-K\u00f6hler-Allee 103,  79110 Freiburg im Breisgau, Germany"}]},{"ORCID":"https:\/\/orcid.org\/0009-0002-9377-3530","authenticated-orcid":false,"given":"Sophia K.","family":"Kilian","sequence":"additional","affiliation":[{"name":"Hahn-Schickard, Georges-K\u00f6hler-Allee 103, 79110 Freiburg im Breisgau, Germany"}]},{"given":"Sebastian","family":"Kluck","sequence":"additional","affiliation":[{"name":"Laboratory of Process Technology, NeptunLab, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-K\u00f6hler-Allee 103,  79110 Freiburg im Breisgau, Germany"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2583-1532","authenticated-orcid":false,"given":"Pegah","family":"Pezeshkpour","sequence":"additional","affiliation":[{"name":"Laboratory of Process Technology, NeptunLab, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-K\u00f6hler-Allee 103,  79110 Freiburg im Breisgau, Germany"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8376-154X","authenticated-orcid":false,"given":"Frederik","family":"Kotz-Helmer","sequence":"additional","affiliation":[{"name":"Laboratory of Process Technology, NeptunLab, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-K\u00f6hler-Allee 103,  79110 Freiburg im Breisgau, Germany"},{"name":"Freiburg Materials Research Center (FMF), University of Freiburg, Stefan-Meier-Stra\u00dfe 21, 79104 Freiburg im Breisgau, Germany"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3955-0291","authenticated-orcid":false,"given":"Bastian E.","family":"Rapp","sequence":"additional","affiliation":[{"name":"Laboratory of Process Technology, NeptunLab, Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-K\u00f6hler-Allee 103,  79110 Freiburg im Breisgau, Germany"},{"name":"Freiburg Materials Research Center (FMF), University of Freiburg, Stefan-Meier-Stra\u00dfe 21, 79104 Freiburg im Breisgau, Germany"},{"name":"FIT Freiburg Center of Interactive Materials and Bioinspired Technologies, University of Freiburg, Georges-K\u00f6hler-Allee 105, 79110 Freiburg im Breisgau, Germany"}]}],"member":"1968","published-online":{"date-parts":[[2024,1,10]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1097","DOI":"10.1002\/adfm.200701216","article-title":"Eutectic Gallium-Indium (EGaIn): A Liquid Metal Alloy for the Formation of Stable Structures in Microchannels at Room Temperature","volume":"18","author":"Dickey","year":"2008","journal-title":"Adv. Funct. Mater."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"18369","DOI":"10.1021\/am5043017","article-title":"Emerging Applications of Liquid Metals Featuring Surface Oxides","volume":"6","author":"Dickey","year":"2014","journal-title":"ACS Appl. Mater. Interfaces"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"4073","DOI":"10.1039\/C7CS00043J","article-title":"Liquid Metals: Fundamentals and Applications in Chemistry","volume":"47","author":"Daeneke","year":"2018","journal-title":"Chem. Soc. Rev."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"2782","DOI":"10.1039\/c2lc21176a","article-title":"Microfluidic Electronics","volume":"12","author":"Cheng","year":"2012","journal-title":"Lab. Chip."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"974","DOI":"10.1039\/C7LC00046D","article-title":"Liquid Metal Enabled Microfluidics","volume":"17","author":"Khoshmanesh","year":"2017","journal-title":"Lab. Chip."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"3304","DOI":"10.1073\/pnas.1319878111","article-title":"Liquid Metal Enabled Pump","volume":"111","author":"Tang","year":"2014","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1900381","DOI":"10.1002\/adem.201900381","article-title":"Artificial Heart Based on Electrically Controlled Non-Toxic Liquid Metal Pump","volume":"21","author":"Li","year":"2019","journal-title":"Adv. Eng. Mater."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"2475","DOI":"10.1039\/D1MH00623A","article-title":"Stimulus-Driven Liquid Metal and Liquid Crystal Network Actuators for Programmable Soft Robotics","volume":"8","author":"Lv","year":"2021","journal-title":"Mater. Horiz."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"5851","DOI":"10.1002\/adfm.201400689","article-title":"Liquid Metal Actuator for Inducing Chaotic Advection","volume":"24","author":"Tang","year":"2014","journal-title":"Adv. Funct. Mater."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"2624","DOI":"10.1002\/adfm.201200324","article-title":"Formation of Spherical and Non-Spherical Eutectic Gallium-Indium Liquid-Metal Microdroplets in Microfluidic Channels at Room Temperature","volume":"22","author":"Hutter","year":"2012","journal-title":"Adv. Funct. Mater."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"604","DOI":"10.1002\/adma.201503875","article-title":"Liquid-Metal Microdroplets Formed Dynamically with Electrical Control of Size and Rate","volume":"28","author":"Tang","year":"2016","journal-title":"Adv. Mater."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"2476","DOI":"10.1039\/C5LC00415B","article-title":"Continuous Transfer of Liquid Metal Droplets across a Fluid\u2013Fluid Interface within an Integrated Microfluidic Chip","volume":"15","author":"Gol","year":"2015","journal-title":"Lab. Chip."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"2201469","DOI":"10.1002\/adma.202201469","article-title":"An On-Chip. Liquid Metal Plug Generator","volume":"34","author":"Bhagwat","year":"2022","journal-title":"Adv. Mater."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"1700141","DOI":"10.1002\/admi.201700141","article-title":"Designing Liquid Metal Interfaces to Enable Next Generation Flexible and Reconfigurable Electronics","volume":"4","author":"Ilyas","year":"2017","journal-title":"Adv. Mater. Interfaces"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"174102","DOI":"10.1063\/1.4764020","article-title":"Reconfigurable Liquid Metal Circuits by Laplace Pressure Shaping","volume":"101","author":"Cumby","year":"2012","journal-title":"Appl. Phys. Lett."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"3501","DOI":"10.1002\/adfm.201303220","article-title":"Direct Writing of Gallium-Indium Alloy for Stretchable Electronics","volume":"24","author":"Boley","year":"2014","journal-title":"Adv. Funct. Mater."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1606425","DOI":"10.1002\/adma.201606425","article-title":"Stretchable and Soft Electronics Using Liquid Metals","volume":"29","author":"Dickey","year":"2017","journal-title":"Adv. Mater."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"194901","DOI":"10.1063\/1.4919605","article-title":"A Reconfigurable Liquid Metal Antenna Driven by Electrochemically Controlled Capillarity","volume":"117","author":"Wang","year":"2015","journal-title":"J. Appl. Phys."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"013501","DOI":"10.1063\/1.3603961","article-title":"A Frequency Shifting Liquid Metal Antenna with Pressure Responsiveness","volume":"99","author":"Hayes","year":"2011","journal-title":"Appl. Phys. Lett."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"6397","DOI":"10.1002\/smll.201502692","article-title":"Handwritten, Soft Circuit Boards and Antennas Using Liquid Metal Nanoparticles","volume":"11","author":"Lin","year":"2015","journal-title":"Small"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"1900530","DOI":"10.1002\/adem.201900530","article-title":"Liquid-Metal-Enhanced Wire Mesh as a Stiffness Variable Material for Making Soft Robotics","volume":"21","author":"Yuan","year":"2019","journal-title":"Adv. Eng. Mater."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"269","DOI":"10.1080\/19475411.2021.1948457","article-title":"3D Printing of Liquid Metal Based Tactile Sensor for Simultaneously Sensing of Temperature and Forces","volume":"12","author":"Wang","year":"2021","journal-title":"Int. J. Smart Nano Mater."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1009","DOI":"10.1007\/s00216-005-0069-7","article-title":"Voltammetric Analysis Using a Self-Renewable Non-Mercury Electrode","volume":"383","author":"Surmann","year":"2005","journal-title":"Anal. Bioanal. Chem."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"1726","DOI":"10.1002\/elan.201400752","article-title":"Anodic Stripping Voltammetry with Galinstan as Working Electrode","volume":"27","author":"Surmann","year":"2015","journal-title":"Electroanalysis"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"2100760","DOI":"10.1002\/admt.202100760","article-title":"Post-Transition Metal Electrodes for Sensing Heavy Metal Ions by Stripping Voltammetry","volume":"7","author":"Zheng","year":"2022","journal-title":"Adv. Mater. Technol."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"386","DOI":"10.1021\/acssensors.1c02606","article-title":"Emerging Role of Liquid Metals in Sensing","volume":"7","author":"Baharfar","year":"2022","journal-title":"ACS Sens."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"144","DOI":"10.1002\/adfm.201200837","article-title":"Liquid Metal Marbles","volume":"23","author":"Sivan","year":"2013","journal-title":"Adv. Funct. Mater."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"3799","DOI":"10.1002\/adfm.201304064","article-title":"Liquid Metal\/Metal Oxide Frameworks","volume":"24","author":"Zhang","year":"2014","journal-title":"Adv. Funct. Mater."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"2000626","DOI":"10.1002\/admi.202000626","article-title":"Galvanic Replacement of Liquid Metal\/Reduced Graphene Oxide Frameworks","volume":"7","author":"Wang","year":"2020","journal-title":"Adv. Mater. Interfaces"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"1706277","DOI":"10.1002\/adfm.201706277","article-title":"Robust Fabrication of Nonstick, Noncorrosive, Conductive Graphene-Coated Liquid Metal Droplets for Droplet-Based, Floating Electrodes","volume":"28","author":"Chen","year":"2018","journal-title":"Adv. Funct. Mater."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"1819","DOI":"10.1007\/s11664-022-10175-y","article-title":"A Disposable Electrochemical Sensor for Lead Ion Detection Based on In Situ Polymerization of Conductive Polypyrrole Coating","volume":"52","author":"Zhang","year":"2023","journal-title":"J. Electron. Mater."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"100203","DOI":"10.1016\/j.talo.2023.100203","article-title":"Electrochemical Determination of Heavy Metal Ions Applying Screen-Printed Electrodes Based Sensors. A Review on Water and Environmental Samples Analysis","volume":"7","author":"Rubino","year":"2023","journal-title":"Talanta Open"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"6313","DOI":"10.1002\/adma.201302820","article-title":"25th Anniversary Article: Galvanic Replacement: A Simple and Versatile Route to Hollow Nanostructures with Tunable and Well-Controlled Properties","volume":"25","author":"Xia","year":"2013","journal-title":"Adv. Mater."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"7135","DOI":"10.1039\/C7CC02352A","article-title":"Galvanic Replacement Reaction: Recent Developments for Engineering Metal Nanostructures towards Catalytic Applications","volume":"53","author":"Rodrigues","year":"2017","journal-title":"Chem. Commun."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"4","DOI":"10.1002\/bkcs.12638","article-title":"Galvanic Replacement Reaction to Prepare Catalytic Materials","volume":"44","author":"Hong","year":"2023","journal-title":"Bull. Korean Chem. Soc."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"1464","DOI":"10.1021\/jacs.6b05957","article-title":"Galvanic Replacement of the Liquid Metal Galinstan","volume":"139","author":"Hoshyargar","year":"2017","journal-title":"J. Am. Chem. Soc."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"10550","DOI":"10.1021\/acs.langmuir.8b02303","article-title":"Tunable Noble Metal Thin Films on Ga Alloys via Galvanic Replacement","volume":"34","author":"David","year":"2018","journal-title":"Langmuir"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"21419","DOI":"10.1039\/C9NR05551G","article-title":"Synthesis of Sub-Micrometer Biphasic Au\u2013AuGa2\/Liquid Metal Frameworks","volume":"11","author":"David","year":"2019","journal-title":"Nanoscale"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"9705","DOI":"10.1039\/C9NR02458A","article-title":"Galvanic Replacement of Liquid Metal Galinstan with Pt for the Synthesis of Electrocatalytically Active Nanomaterials","volume":"11","author":"Oloye","year":"2019","journal-title":"Nanoscale"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"19283","DOI":"10.1021\/jacs.0c09458","article-title":"Exploring the Chemical Reactivity of Gallium Liquid Metal Nanoparticles in Galvanic Replacement","volume":"142","author":"Stoian","year":"2020","journal-title":"J. Am. Chem. Soc."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"1571","DOI":"10.1021\/acs.chemmater.0c03969","article-title":"Facile Synthesis of a Library of Hollow Metallic Particles through the Galvanic Replacement of Liquid Gallium","volume":"33","author":"Falchevskaya","year":"2021","journal-title":"Chem. Mater."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"5891","DOI":"10.1039\/D2NR06733A","article-title":"Coating of Gallium-Based Liquid Metal Particles with Molybdenum Oxide and Oxysulfide for Electronic Band Structure Modulation","volume":"15","author":"Ghasemian","year":"2023","journal-title":"Nanoscale"},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"4291","DOI":"10.1039\/D2NR06384K","article-title":"Formation of Inorganic Liquid Gallium Particle\u2013Manganese Oxide Composites","volume":"15","author":"Cai","year":"2023","journal-title":"Nanoscale"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"2104298","DOI":"10.1002\/adma.202104298","article-title":"A Liquid Metal Mediated Metallic Coating for Antimicrobial and Antiviral Fabrics","volume":"33","author":"Kwon","year":"2021","journal-title":"Adv. Mater."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"2300751","DOI":"10.1002\/smll.202300751","article-title":"Nanoheterostructure by Liquid Metal Sandwich-Based Interfacial Galvanic Replacement for Cancer Targeted Theranostics","volume":"19","author":"Guo","year":"2023","journal-title":"Small"},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"2008024","DOI":"10.1002\/adma.202008024","article-title":"General Programmable Growth of Hybrid Core\u2013Shell Nanostructures with Liquid Metal Nanodroplets","volume":"33","author":"Ren","year":"2021","journal-title":"Adv. Mater."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"15459","DOI":"10.1021\/acsami.6b01896","article-title":"Photolithography-Based Patterning of Liquid Metal Interconnects for Monolithically Integrated Stretchable Circuits","volume":"8","author":"Park","year":"2016","journal-title":"ACS Appl. Mater. Interfaces"},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"766","DOI":"10.1021\/ed400722e","article-title":"A Student-Made Silver\u2013Silver Chloride Reference Electrode for the General Chemistry Laboratory: \u223c10 Min Preparation","volume":"91","author":"Barlag","year":"2014","journal-title":"J. Chem. Educ."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/24\/2\/416\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T13:43:39Z","timestamp":1760103819000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/24\/2\/416"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2024,1,10]]},"references-count":48,"journal-issue":{"issue":"2","published-online":{"date-parts":[[2024,1]]}},"alternative-id":["s24020416"],"URL":"https:\/\/doi.org\/10.3390\/s24020416","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2024,1,10]]}}}