title: 3D imaging of flow patterns in an internally-pumped microfluidic device: redox magnetohydrodynamics and electrochemically-generated density gradients.
abstract: Redox magnetohydrodynamics (MHD) is a promising technique for developing new electrochemical-based microfluidic flow devices with unique capabilities, such as easily switching flow direction and adjusting flow speeds and flow patterns as well as avoiding bubble formation. However, a detailed description of all the forces involved and predicting flow patterns in confined geometries is lacking. In addition to redox-MHD, density gradients caused by the redox reactions also play important roles. Flow in these devices with small fluid volumes has mainly been characterized by following microbead motion by optical microscopy either by particle tracking velocimetry (PTV) or by processing the microbead images by particle image velocimetry (PIV) software. This approach has limitations in spatial resolution and dimensionality. Here we use fluorescence correlation spectroscopy (FCS) to quantitatively and accurately measure flow speeds and patterns in the ~5-50 μm/s range in redox-MHD-based microfluidic devices, from which 3D flow maps are obtained with a spatial resolution down to 2 μm. The 2 μm spatial resolution flow speeds map revealed detailed flow profiles during redox-MHD in which the velocity increases linearly from above the electrode and reaches a plateau across the center of the cell. By combining FCS and video-microscopy (with PTV and PIV processing approaches), we are able to quantify a vertical flow of ~10 μm/s above the electrodes as a result of density gradients caused by the redox reactions and follow convection flow patterns. Overall, combining FCS, PIV, and PTV analysis of redox-MHD is a powerful combination to more thoroughly characterize the underlying forces in these promising microfluidic devices.
authors.affiliation: Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701, United States.
authors.forename: Feng
authors.initials: F
authors.lastname: Gao
authors.forename: Adam
authors.initials: A
authors.lastname: Kreidermacher
authors.forename: Ingrid
authors.initials: I
authors.lastname: Fritsch
authors.forename: Colin D
authors.initials: CD
authors.lastname: Heyes
mesh_terms: D055664:Electrochemical Techniques / Q000295:instrumentation; D004566:Electrodes; D057446:Hydrodynamics; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation; D010084:Oxidation-Reduction
references.citation: Lab Chip. 2009 Sep 7;9(17):2551-67
references.pmid: 19680579
references.citation: Lab Chip. 2004 Dec;4(6):526-33
references.pmid: 15570361
references.citation: Anal Chem. 2010 May 1;82(9):3411-8
references.pmid: 20380431
references.citation: Biopolymers. 1974 Jan;13(1):29-61
references.pmid: 4818131
references.citation: Appl Spectrosc. 2011 Apr;65(4):115A-124A
references.pmid: 21396180
references.citation: Microfluid Nanofluidics. 2009 Feb 1;6(2):145
references.pmid: 20126306
references.citation: Anal Chem. 2000 Jul 15;72(14):3260-5
references.pmid: 10939397
references.citation: Annu Rev Biophys Biomol Struct. 2007;36:151-69
references.pmid: 17477838
references.citation: Isr J Chem. 2010 Apr 1;49(3-4):293-301
references.pmid: 21116454
references.citation: Anal Chem. 2001 Aug 15;73(16):3981-92
references.pmid: 11534726
references.citation: Lab Chip. 2010 May 21;10(10):1286-92
references.pmid: 20445882
references.citation: Anal Chem. 2011 May 1;83(9):3275-81
references.pmid: 21526858
references.citation: J Biomed Opt. 2007 Jan-Feb;12(1):014034
references.pmid: 17343509
references.citation: ACS Nano. 2011 Nov 22;5(11):9062-73
references.pmid: 22023370
references.citation: Lab Chip. 2005 Jul;5(7):785-91
references.pmid: 15970973
references.citation: J Biomed Opt. 2009 Mar-Apr;14(2):024049
references.pmid: 19405777
references.citation: Anal Chem. 2010 Sep 1;82(17):7068-72
references.pmid: 20681513
references.citation: Anal Chem. 2009 Jan 15;81(2):746-54
references.pmid: 19093758
references.citation: Anal Chem. 2010 Apr 1;82(7):2643-51
references.pmid: 20210341
references.citation: Anal Chem. 2012 Nov 6;84(21):9402-9
references.pmid: 23057608
references.citation: Appl Spectrosc. 2004 Oct;58(10):1180-6
references.pmid: 15527518
references.citation: Mech Res Commun. 2009 Jan 1;36(1):10-21
references.pmid: 20046890