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Tahmasebi A, Habibi S, Collins JL, An R, Dehdashti E, Minerick AR. pH Gradients in Spatially Non-Uniform AC Electric Fields around the Charging Frequency; A Study of Two Different Geometries and Electrode Passivation. MICROMACHINES 2023; 14:1655. [PMID: 37763818 PMCID: PMC10534923 DOI: 10.3390/mi14091655] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Revised: 08/15/2023] [Accepted: 08/16/2023] [Indexed: 09/29/2023]
Abstract
Dielectrophoresis (DEP), a precision nonlinear electrokinetic tool utilized within microfluidic devices, can induce bioparticle polarization that manifests as motion in the electric field; this phenomenon has been leveraged for phenotypic cellular and biomolecular detection, making DEP invaluable for diagnostic applications. As device operation times lengthen, reproducibility and precision decrease, which has been postulated to be caused by ion gradients within the supporting electrolyte medium. This research focuses on characterizing pH gradients above, at, and below the electrode charging frequency (0.2-1.4 times charging frequency) in an aqueous electrolyte solution in order to extend the parameter space for which microdevice-imposed artifacts on cells in clinical diagnostic devices have been characterized. The nonlinear alternating current (AC) electric fields (0.07 Vpp/μm) required for DEP were generated via planar T-shaped and star-shaped microelectrodes overlaid by a 70 μm high microfluidic chamber. The experiments were designed to quantify pH changes temporally and spatially in the two microelectrode geometries. In parallel, a 50 nm hafnium oxide (HfO2) thin film on the microelectrodes was tested to provide insights into the role of Faradaic surface reactions on the pH. Electric field simulations were conducted to provide insights into the gradient shape within the microelectrode geometries. Frequency dependence was also examined to ascertain ion electromigration effects above, at, and below the electrode charging frequency. The results revealed Faradaic reactions above, at, and below the electrode charging frequency. Comparison experiments further demonstrated that pH changes caused by Faradaic reactions increased inversely with frequency and were more pronounced in the star-shaped geometry. Finally, HfO2 films demonstrated frequency-dependent properties, impeding Faradaic reactions.
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Affiliation(s)
- Azade Tahmasebi
- Department of Chemical Engineering, Michigan Technological University, Houghton, MI 49931, USA
| | - Sanaz Habibi
- Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109, USA
| | - Jeana L Collins
- Department of Chemical Engineering, Michigan Technological University, Houghton, MI 49931, USA
| | - Ran An
- Department of Chemical Engineering, University of Houston, Houston, TX 77204, USA
| | - Esmaeil Dehdashti
- Department of Chemical Engineering, Michigan Technological University, Houghton, MI 49931, USA
| | - Adrienne Robyn Minerick
- Department of Chemical Engineering, Michigan Technological University, Houghton, MI 49931, USA
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Li T, Díaz-Real JA, Holm T. Design of Electrochemical Microfluidic Detectors: Accurate Potential Measurement. ACS Sens 2022; 7:2934-2939. [PMID: 36129391 DOI: 10.1021/acssensors.2c00785] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Potential drop due to the electrolyte conductivity between the reference electrode (RE) and the working electrode leads to measurement error. Because of the limited amount of electrolyte and constricted geometry in microfluidic systems, the total potential drop in a microfluidic system is confined within a small part of the cell. This makes the choice and placement of the RE an important consideration. In this article, we discuss ways to incorporate an RE in a microfluidic system and, through numerical modeling and experimental verification, present some design strategies for electrode placement to ensure accurate potential control.
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Affiliation(s)
- Tianyu Li
- Department of Mechanical and Industrial Engineering, University of Toronto, 5 King's College Rd, Toronto, Ontario M5S 3G8, Canada
| | - Jesús Adrián Díaz-Real
- Centro de Investigación y Desarrollo Tecnológico en Electroquímica, S.C. Parque Tecnológico Querétaro, S/N, Sanfandila, C.P. 76703, Pedro Escobedo, Querétaro, México
| | - Thomas Holm
- Institute for Energy Technology, P.O. Box 40, Kjeller NO-2027, Norway
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3
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Weiß LJK, Music E, Rinklin P, Banzet M, Mayer D, Wolfrum B. On-Chip Electrokinetic Micropumping for Nanoparticle Impact Electrochemistry. Anal Chem 2022; 94:11600-11609. [PMID: 35900877 DOI: 10.1021/acs.analchem.2c02017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Single-entity electrochemistry is a powerful technique to study the interactions of nanoparticles at the liquid-solid interface. In this work, we exploit Faradaic (background) processes in electrolytes of moderate ionic strength to evoke electrokinetic transport and study its influence on nanoparticle impacts. We implemented an electrode array comprising a macroscopic electrode that surrounds a set of 62 spatially distributed microelectrodes. This configuration allowed us to alter the global electrokinetic transport characteristics by adjusting the potential at the macroscopic electrode, while we concomitantly recorded silver nanoparticle impacts at the microscopic detection electrodes. By focusing on temporal changes of the impact rates, we were able to reveal alterations in the macroscopic particle transport. Our findings indicate a potential-dependent micropumping effect. The highest impact rates were obtained for strongly negative macroelectrode potentials and alkaline solutions, albeit also positive potentials lead to an increase in particle impacts. We explain this finding by reversal of the pumping direction. Variations in the electrolyte composition were shown to play a critical role as the macroelectrode processes can lead to depletion of ions, which influences both the particle oxidation and the reactions that drive the transport. Our study highlights that controlled on-chip micropumping is possible, yet its optimization is not straightforward. Nevertheless, the utilization of electro- and diffusiokinetic transport phenomena might be an appealing strategy to enhance the performance in future impact-based sensing applications.
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Affiliation(s)
- Lennart J K Weiß
- Neuroelectronics - Munich Institute of Biomedical Engineering, Department of Electrical Engineering, TUM School of Computation, Information and Technology, Technical University of Munich, Boltzmannstrasse 11, Garching 85748, Germany
| | - Emir Music
- Neuroelectronics - Munich Institute of Biomedical Engineering, Department of Electrical Engineering, TUM School of Computation, Information and Technology, Technical University of Munich, Boltzmannstrasse 11, Garching 85748, Germany
| | - Philipp Rinklin
- Neuroelectronics - Munich Institute of Biomedical Engineering, Department of Electrical Engineering, TUM School of Computation, Information and Technology, Technical University of Munich, Boltzmannstrasse 11, Garching 85748, Germany
| | - Marko Banzet
- Institute of Biological Information Processing, Bioelectronics (IBI-3), Forschungszentrum Jülich, Jülich 52425, Germany
| | - Dirk Mayer
- Institute of Biological Information Processing, Bioelectronics (IBI-3), Forschungszentrum Jülich, Jülich 52425, Germany
| | - Bernhard Wolfrum
- Neuroelectronics - Munich Institute of Biomedical Engineering, Department of Electrical Engineering, TUM School of Computation, Information and Technology, Technical University of Munich, Boltzmannstrasse 11, Garching 85748, Germany
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4
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Wahyuni WT, Putra BR, Marken F. Voltammetric detection of vitamin B1 (thiamine) in neutral solution at a glassy carbon electrode via in situ pH modulation. Analyst 2020; 145:1903-1909. [DOI: 10.1039/c9an02186h] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Pretreatment of glassy carbon electrode at an appropriate negative potential provide hydroxide ion which contributes to the in situ pH modulation of the electrode for thiamine detection in neutral solution.
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Affiliation(s)
- Wulan Tri Wahyuni
- Department of Chemistry
- Faculty of Mathematics and Natural Sciences
- IPB University (Bogor Agricultural University)
- Bogor
- Indonesia
| | - Budi Riza Putra
- Department of Chemistry
- Faculty of Mathematics and Natural Sciences
- IPB University (Bogor Agricultural University)
- Bogor
- Indonesia
| | - Frank Marken
- Department of Chemistry
- University of Bath
- Somerset
- UK
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5
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Abadie T, Sella C, Perrodin P, Thouin L. Electrochemical Generation and Detection of Transient Concentration Gradients in Microfluidic Channels. Theoretical and Experimental Investigations. Front Chem 2019; 7:704. [PMID: 31709233 PMCID: PMC6822297 DOI: 10.3389/fchem.2019.00704] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2019] [Accepted: 10/08/2019] [Indexed: 12/21/2022] Open
Abstract
Transient concentration gradients generated and detected electrochemically in continuous flow microchannels were investigated by numerical simulations and amperometric measurements. Operating conditions including device geometry and hydrodynamic regime were theoretically delineated for producing gradients of various profiles with tunable characteristics. Experiments were carried out with microfluidic devices incorporating a dual-channel-electrode configuration. Under these conditions, high electrochemical performance was achieved both to generate concentration gradients and to monitor their dynamics along linear microchannels. Good agreement was observed between simulated and experimental data validating predictions between gradient properties and generation conditions. These results demonstrated the capability of electrochemical microdevices to produce in situ tunable concentration gradients with real-time monitoring. This approach is versatile for the active control in microfluidics of microenvironments or chemical gradients with high spatiotemporal resolution.
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Affiliation(s)
| | | | | | - Laurent Thouin
- PASTEUR, Département de chimie, École normale supérieure, PSL University, Sorbonne Université, CNRS, Paris, France
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Read TL, Joseph MB, Macpherson JV. Manipulation and measurement of pH sensitive metal–ligand binding using electrochemical proton generation and metal detection. Chem Commun (Camb) 2016; 52:1863-6. [DOI: 10.1039/c5cc09326k] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Boron doped diamond generator-detector electrodes can both change and monitor the binding state of the pH sensitive metal–ligand complex [Cu2+:TETA] by locally varying pH and measuring the free metal concentration.
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Affiliation(s)
- Tania L. Read
- Department of Chemistry
- University of Warwick
- Coventry
- UK
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Xu W, Ma C, Bohn PW. Coupling of Independent Electrochemical Reactions and Fluorescence at Closed Bipolar Interdigitated Electrode Arrays. ChemElectroChem 2015. [DOI: 10.1002/celc.201500366] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- Wei Xu
- Department of Chemistry and Biochemistry University of Notre Dame Notre Dame IN 46556 USA
| | - Chaoxiong Ma
- Department of Chemistry and Biochemistry University of Notre Dame Notre Dame IN 46556 USA
| | - Paul W. Bohn
- Department of Chemistry and Biochemistry University of Notre Dame Notre Dame IN 46556 USA
- Department of Chemical and Biomolecular Engineering University of Notre Dame Notre Dame IN 46556 USA
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8
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Hongxia B, Ruiyi L, Zaijun L, Junkang L, Zhiguo G, Guangli W. Fabrication of a high density graphene aerogel–gold nanostar hybrid and its application for the electrochemical detection of hydroquinone and o-dihydroxybenzene. RSC Adv 2015. [DOI: 10.1039/c5ra06196b] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
We report the first synthesis of a high density graphene aerogel–gold nanostar hybrid with excellent mechanical and electrical properties and its application in the electrochemical detection of hydroquinone and o-dihydroxybenzene.
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Affiliation(s)
- Bei Hongxia
- School of Chemical and Material Engineering
- Jiangnan University
- Wuxi
- China
| | - Li Ruiyi
- School of Chemical and Material Engineering
- Jiangnan University
- Wuxi
- China
| | - Li Zaijun
- School of Chemical and Material Engineering
- Jiangnan University
- Wuxi
- China
- Key Laboratory of Food Colloids and Biotechnology
| | - Liu Junkang
- School of Chemical and Material Engineering
- Jiangnan University
- Wuxi
- China
| | - Gu Zhiguo
- School of Chemical and Material Engineering
- Jiangnan University
- Wuxi
- China
| | - Wang Guangli
- School of Chemical and Material Engineering
- Jiangnan University
- Wuxi
- China
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9
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An R, Massa K, Wipf DO, Minerick AR. Solution pH change in non-uniform alternating current electric fields at frequencies above the electrode charging frequency. BIOMICROFLUIDICS 2014; 8:064126. [PMID: 25553200 PMCID: PMC4272385 DOI: 10.1063/1.4904059] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2014] [Accepted: 12/02/2014] [Indexed: 05/23/2023]
Abstract
AC Faradaic reactions have been reported as a mechanism inducing non-ideal phenomena such as flow reversal and cell deformation in electrokinetic microfluidic systems. Prior published work described experiments in parallel electrode arrays below the electrode charging frequency (fc ), the frequency for electrical double layer charging at the electrode. However, 2D spatially non-uniform AC electric fields are required for applications such as in plane AC electroosmosis, AC electrothermal pumps, and dielectrophoresis. Many microscale experimental applications utilize AC frequencies around or above fc . In this work, a pH sensitive fluorescein sodium salt dye was used to detect [H(+)] as an indicator of Faradaic reactions in aqueous solutions within non-uniform AC electric fields. Comparison experiments with (a) parallel (2D uniform fields) electrodes and (b) organic media were employed to deduce the electrode charging mechanism at 5 kHz (1.5fc ). Time dependency analysis illustrated that Faradaic reactions exist above the theoretically predicted electrode charging frequency. Spatial analysis showed [H(+)] varied spatially due to electric field non-uniformities and local pH changed at length scales greater than 50 μm away from the electrode surface. Thus, non-uniform AC fields yielded spatially varied pH gradients as a direct consequence of ion path length differences while uniform fields did not yield pH gradients; the latter is consistent with prior published data. Frequency dependence was examined from 5 kHz to 12 kHz at 5.5 Vpp potential, and voltage dependency was explored from 3.5 to 7.5 Vpp at 5 kHz. Results suggest that Faradaic reactions can still proceed within electrochemical systems in the absence of well-established electrical double layers. This work also illustrates that in microfluidic systems, spatial medium variations must be considered as a function of experiment time, initial medium conditions, electric signal potential, frequency, and spatial position.
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Affiliation(s)
- Ran An
- Department of Chemical Engineering, Michigan Technological University , Houghton, Michigan 49931, USA
| | - Katherine Massa
- Department of Chemical Engineering, Michigan Technological University , Houghton, Michigan 49931, USA
| | - David O Wipf
- Department of Chemistry, Mississippi State University , Mississippi State, Mississippi 39762, USA
| | - Adrienne R Minerick
- Department of Chemical Engineering, Michigan Technological University , Houghton, Michigan 49931, USA
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10
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Contento NM, Bohn PW. Tunable electrochemical pH modulation in a microchannel monitored via the proton-coupled electro-oxidation of hydroquinone. BIOMICROFLUIDICS 2014; 8:044120. [PMID: 25379105 PMCID: PMC4189302 DOI: 10.1063/1.4894275] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Accepted: 08/19/2014] [Indexed: 05/30/2023]
Abstract
Electrochemistry is a promising tool for microfluidic systems because it is relatively inexpensive, structures are simple to fabricate, and it is straight-forward to interface electronically. While most widely used in microfluidics for chemical detection or as the transduction mechanism for molecular probes, electrochemical methods can also be used to efficiently alter the chemical composition of small (typically <100 nl) microfluidic volumes in a manner that improves or enables subsequent measurements and sample processing steps. Here, solvent (H2O) electrolysis is performed quantitatively at a microchannel Pt band electrode to increase microchannel pH. The change in microchannel pH is simultaneously tracked at a downstream electrode by monitoring changes in the i-V characteristics of the proton-coupled electro-oxidation of hydroquinone, thus providing real-time measurement of the protonated forms of hydroquinone from which the pH can be determined in a straightforward manner. Relative peak heights for protonated and deprotonated hydroquinone forms are in good agreement with expected pH changes by measured electrolysis rates, demonstrating that solvent electrolysis can be used to provide tunable, quantitative pH control within a microchannel.
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Affiliation(s)
- Nicholas M Contento
- Department of Chemical and Biomolecular Engineering, University of Notre Dame , Notre Dame, Indiana 46556, USA
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