{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T04:19:51Z","timestamp":1760242791103,"version":"build-2065373602"},"reference-count":41,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2016,7,21]],"date-time":"2016-07-21T00:00:00Z","timestamp":1469059200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100003725","name":"National Research Foundation of Korea","doi-asserted-by":"publisher","award":["NRF 2014R1A2A2A01003618","NRF-2016R1A2B4006987"],"award-info":[{"award-number":["NRF 2014R1A2A2A01003618","NRF-2016R1A2B4006987"]}],"id":[{"id":"10.13039\/501100003725","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Micromachines"],"abstract":"<jats:p>We describe a quantitative study of vortex generation due to non-equilibrium electrokinetics near a micro\/nanochannel interface. The microfluidic device is comprised of a microchannel with a set of nanochannels. These perm-selective nanochannels induce flow instability and thereby produce strong vortex generation. We performed tracking visualization of fluorescent microparticles to obtain velocity fields. Particle tracking enables the calculation of an averaged velocity field and the velocity fluctuations. We characterized the effect of applied voltages and electrolyte concentrations on vortex formation. The experimental results show that an increasing voltage or decreasing concentration results in a larger vortex region and a strong velocity fluctuation. We calculate the normalized velocity fluctuation\u2014whose meaning is comparable to turbulent intensity\u2014and we found that it is as high as 0.12. This value is indicative of very efficient mixing, albeit with a small Reynolds number.<\/jats:p>","DOI":"10.3390\/mi7070127","type":"journal-article","created":{"date-parts":[[2016,7,21]],"date-time":"2016-07-21T09:48:05Z","timestamp":1469094485000},"page":"127","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Quantification of Vortex Generation Due to Non-Equilibrium Electrokinetics at the Micro\/Nanochannel Interface: Particle Tracking Velocimetry"],"prefix":"10.3390","volume":"7","author":[{"given":"Seung","family":"Lee","sequence":"first","affiliation":[{"name":"Department of Mechanical Engineering, Sogang University, Seoul 04107, Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kilsung","family":"Kwon","sequence":"additional","affiliation":[{"name":"Department of Mechanical Engineering, Sogang University, Seoul 04107, Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4882-9040","authenticated-orcid":false,"given":"Tae-Joon","family":"Jeon","sequence":"additional","affiliation":[{"name":"Department of Biological Engineering, Inha University, Incheon 22212, Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8420-637X","authenticated-orcid":false,"given":"Sun","family":"Kim","sequence":"additional","affiliation":[{"name":"Department of Mechanical Engineering, Inha University, Incheon 22212, Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Daejoong","family":"Kim","sequence":"additional","affiliation":[{"name":"Department of Mechanical Engineering, Sogang University, Seoul 04107, Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2016,7,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1073","DOI":"10.1039\/B909366B","article-title":"Nanofluidics, from bulk to interfaces","volume":"39","author":"Bocquet","year":"2010","journal-title":"Chem. Soc. Rev."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"249","DOI":"10.1007\/s10404-004-0012-9","article-title":"Nanofluidics: What is it and what can we expect from it?","volume":"1","author":"Eijkel","year":"2005","journal-title":"Microfluid. Nanofluid."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1060","DOI":"10.1039\/B900409M","article-title":"Nanofluidics in chemical analysis","volume":"39","author":"Piruska","year":"2010","journal-title":"Chem. Soc. Rev."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"387","DOI":"10.1038\/nature05061","article-title":"Future lab-on-a-chip technologies for interrogating individual molecules","volume":"442","author":"Craighead","year":"2006","journal-title":"Nature"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"210","DOI":"10.1038\/nrd1985","article-title":"Lab-on-a-chip: Microfluidics in drug discovery","volume":"5","author":"Dittrich","year":"2006","journal-title":"Nat. Rev. Drug Discov."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"1153","DOI":"10.1039\/b820557b","article-title":"Microfluidic lab-on-a-chip platforms: Requirements, characteristics and applications","volume":"39","author":"Mark","year":"2010","journal-title":"Chem. Soc. Rev."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"3143","DOI":"10.1039\/C4LC00325J","article-title":"Physics and technological aspects of nanofluidics","volume":"14","author":"Bocquet","year":"2014","journal-title":"Lab Chip"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"4068","DOI":"10.1021\/ac4026303","article-title":"Extended-nanofluidics: Fundamental technologies, unique liquid properties, and application in chemical and bio analysis methods and devices","volume":"86","author":"Mawatari","year":"2014","journal-title":"Anal. Chem."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"317","DOI":"10.1146\/annurev-anchem-071213-020155","article-title":"Microfluidic systems with ion-selective membranes","volume":"7","author":"Slouka","year":"2014","journal-title":"Annu. Rev. Anal. Chem."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"138101","DOI":"10.1103\/PhysRevLett.108.138101","article-title":"Concentration polarization in translocation of DNA through nanopores and nanochannels","volume":"108","author":"Das","year":"2012","journal-title":"Phys. Rev. Lett."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"3586","DOI":"10.1039\/b914466h","article-title":"Micro contactor based on isotachophoretic sample transport","volume":"9","author":"Goet","year":"2009","journal-title":"Lab Chip"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"693","DOI":"10.1007\/s10404-014-1357-3","article-title":"Nafion-film-based micro-nanofluidic device for concurrent DNA preconcentration and separation in free solution","volume":"17","author":"Song","year":"2014","journal-title":"Microfluid. Nanofluid."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"751","DOI":"10.1002\/elps.201100493","article-title":"Effects of microchannel geometry on preconcentration intensity in microfluidic chips with straight or convergent\u2013divergent microchannels","volume":"33","author":"Chen","year":"2012","journal-title":"Electrophoresis"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"3011","DOI":"10.1002\/adma.200701715","article-title":"Non-lithographic wrinkle nanochannels for protein preconcentration","volume":"20","author":"Chung","year":"2008","journal-title":"Adv. Mater."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"7870","DOI":"10.1021\/ac061170i","article-title":"High-throughput positive-dielectrophoretic bioparticle microconcentrator","volume":"78","author":"Gadish","year":"2006","journal-title":"Anal. Chem."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"267","DOI":"10.1021\/ac202501v","article-title":"Propagating concentration polarization and ionic current rectification in a nanochannel\u2013nanofunnel device","volume":"84","author":"Hlushkou","year":"2011","journal-title":"Anal. Chem."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"276","DOI":"10.1016\/j.snb.2015.10.055","article-title":"Preconcentration of lipid vesicles using concentration polarization in a microfluidic chip","volume":"229","author":"Lee","year":"2016","journal-title":"Sens. Actuators B Chem."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"4779","DOI":"10.1021\/ac060031y","article-title":"Electrokinetic protein preconcentration using a simple glass\/poly (dimethylsiloxane) microfluidic chip","volume":"78","author":"Kim","year":"2006","journal-title":"Anal. Chem."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"1351","DOI":"10.1039\/c0lc00349b","article-title":"Massively parallel concentration device for multiplexed immunoassays","volume":"11","author":"Ko","year":"2011","journal-title":"Lab Chip"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"4472","DOI":"10.1039\/c2lc21238b","article-title":"Nanofluidic preconcentration device in a straight microchannel using ion concentration polarization","volume":"12","author":"Ko","year":"2012","journal-title":"Lab Chip"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"9989","DOI":"10.1021\/ac102149f","article-title":"Microfluidic protein preconcentrator using a microchannel-integrated nafion strip: Experiment and modeling","volume":"82","author":"Shen","year":"2010","journal-title":"Anal. Chem."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"625","DOI":"10.1039\/b717268k","article-title":"Non-equilibrium electrokinetic micro\/nanofluidic mixer","volume":"8","author":"Kim","year":"2008","journal-title":"Lab Chip"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"897","DOI":"10.1007\/s10404-011-0918-y","article-title":"Millisecond-order rapid micromixing with non-equilibrium electrokinetic phenomena","volume":"12","author":"Lee","year":"2012","journal-title":"Microfluid. Nanofluid."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"647","DOI":"10.1126\/science.1066238","article-title":"Chaotic mixer for microchannels","volume":"295","author":"Stroock","year":"2002","journal-title":"Science"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"3144","DOI":"10.1002\/elps.200900162","article-title":"Enhancement of electrokinetically driven microfluidic t-mixer using frequency modulated electric field and channel geometry effects","volume":"30","author":"Yan","year":"2009","journal-title":"Electrophoresis"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"839","DOI":"10.1007\/s10404-012-1116-2","article-title":"Electrokinetic Micromixing of Charged and Non-Charged Samples near Nano-\/Microchannel Junction","volume":"14","author":"Chiu","year":"2013","journal-title":"Microfluid. Nanofluid."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"631","DOI":"10.1007\/s10404-008-0281-9","article-title":"Formation of Ionic Depletion\/Enrichment Zones in a Hybrid Micro-\/Nano-channel","volume":"5","author":"Huang","year":"2008","journal-title":"Microfluid. Nanofluid."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"4862","DOI":"10.1002\/elps.200800392","article-title":"A Nanochannel-Based Concentrator Utilizing Concentration Polarization Effect","volume":"29","author":"Huang","year":"2008","journal-title":"Electrophoresis"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"501","DOI":"10.1007\/s10404-007-0178-z","article-title":"Electrokinetic Mixing in Microfluidic Systems (Invited Review Paper)","volume":"3","author":"Chang","year":"2007","journal-title":"Microfluid. Nanofluid."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"173","DOI":"10.1017\/S0022112007004880","article-title":"Electro-osmotic slip and electroconvective instability","volume":"579","author":"Zaltzman","year":"2007","journal-title":"J. Fluid Mech."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"011002","DOI":"10.1103\/PhysRevE.91.011002","article-title":"Bridging the gap between an isolated nanochannel and a communicating multipore heterogeneous membrane","volume":"91","author":"Green","year":"2015","journal-title":"Phys. Rev. E"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"758","DOI":"10.1002\/elps.201100501","article-title":"Ion concentration polarization near microchannel\u2013nanochannel interfaces: Effect of ph value","volume":"33","author":"Chang","year":"2012","journal-title":"Electrophoresis"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"7759","DOI":"10.1021\/la900332v","article-title":"Amplified electrokinetic response by concentration polarization near nanofluidic channel","volume":"25","author":"Kim","year":"2009","journal-title":"Langmuir"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"912","DOI":"10.1039\/b822556g","article-title":"Nanofluidic concentration devices for biomolecules utilizing ion concentration polarization: Theory, fabrication, and applications","volume":"39","author":"Kim","year":"2010","journal-title":"Chem. Soc. Rev."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"044501","DOI":"10.1103\/PhysRevLett.99.044501","article-title":"Concentration polarization and nonlinear electrokinetic flow near a nanofluidic channel","volume":"99","author":"Kim","year":"2007","journal-title":"Phys. Rev. Lett."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"3898","DOI":"10.1021\/la803317p","article-title":"On the propagation of concentration polarization from microchannel-nanochannel interfaces part I: Analytical model and characteristic analysis","volume":"25","author":"Mani","year":"2009","journal-title":"Langmuir"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"117","DOI":"10.1016\/j.cis.2010.06.001","article-title":"Extended space charge in concentration polarization","volume":"159","author":"Rubinstein","year":"2010","journal-title":"Adv. Colloid Interface Sci."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"1014","DOI":"10.1039\/b902074h","article-title":"Theory and experiments of concentration polarization and ion focusing at microchannel and nanochannel interfaces","volume":"39","author":"Zangle","year":"2010","journal-title":"Chem. Soc. Rev."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"109","DOI":"10.3390\/mi7070109","article-title":"Quantification of vortex generation due to non-equilibrium electrokinetics at the micro\/nanochannel interface: Spectral analysis","volume":"7","author":"Lee","year":"2016","journal-title":"Micromachines"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"4040","DOI":"10.1039\/c3lc50674f","article-title":"Electrokinetic tweezing: Three-dimensional manipulation of microparticles by real-time imaging and flow control","volume":"13","author":"Cummins","year":"2013","journal-title":"Lab Chip"},{"key":"ref_41","doi-asserted-by":"crossref","unstructured":"Pope, S.B. (2000). Turbulent Flows, Cambridge University Press.","DOI":"10.1017\/CBO9780511840531"}],"container-title":["Micromachines"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-666X\/7\/7\/127\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T19:26:42Z","timestamp":1760210802000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-666X\/7\/7\/127"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2016,7,21]]},"references-count":41,"journal-issue":{"issue":"7","published-online":{"date-parts":[[2016,7]]}},"alternative-id":["mi7070127"],"URL":"https:\/\/doi.org\/10.3390\/mi7070127","relation":{},"ISSN":["2072-666X"],"issn-type":[{"type":"electronic","value":"2072-666X"}],"subject":[],"published":{"date-parts":[[2016,7,21]]}}}