1
|
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.
Collapse
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
| |
Collapse
|
2
|
González-Gómez CD, Rica RA, Ruiz-Reina E. Electrothermoplasmonic flow in gold nanoparticles suspensions: Nonlinear dependence of flow velocity on aggregate concentration. J Colloid Interface Sci 2023; 648:397-405. [PMID: 37302223 DOI: 10.1016/j.jcis.2023.05.198] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Revised: 05/22/2023] [Accepted: 05/31/2023] [Indexed: 06/13/2023]
Abstract
Efficient mixing and pumping of liquids at the microscale is a technology that is still to be optimized. The combination of an AC electric field with a small temperature gradient leads to a strong electrothermal flow that can be used for multiple purposes. Combining simulations and experiments, an analysis of the performance of electrothermal flow is provided when the temperature gradient is generated by illuminating plasmonic nanoparticles in suspension with a near-resonance laser. Fluid flow is measured by tracking the velocity of fluorescent tracer microparticles in suspension as a function of the electric field, laser power, and concentration of plasmonic particles. Among other results, a non-linear relationship is found between the velocity of the fluid and particle concentration, which is justified in terms of multiple scattering-absorption events, involving aggregates of nanoparticles, that lead to enhanced absorption when the concentration is raised. Simulations provide a description of the phenomenon that is compatible with experiments and constitute a way to understand and estimate the absorption and scattering cross-sections of both dispersed particles and/or aggregates. A comparison of experiments and simulations suggests that there is some aggregation of the gold nanoparticles by forming clusters of about 2-7 particles, but no information about their structure can be obtained without further theoretical and experimental developments. This nonlinear behavior could be useful to get very high ETP velocities by inducing some controlled aggregation of the particles.
Collapse
Affiliation(s)
- Carlos David González-Gómez
- Universidad de Granada, Department of Applied Physics, Nanoparticles Trapping Laboratory, 18071, Granada, Spain; Universidad de Málaga, Department of Applied Physics II, 29071, Málaga, Spain
| | - Raúl A Rica
- Universidad de Granada, Department of Applied Physics, Nanoparticles Trapping Laboratory, 18071, Granada, Spain; Universidad de Granada, Research Unit "Modeling Nature" (MNat), 18071, Granada, Spain
| | - Emilio Ruiz-Reina
- Universidad de Málaga, Department of Applied Physics II, 29071, Málaga, Spain; Universidad de Málaga, Department of Applied Physics II, Institute Carlos I for Theoretical and Computational Physics (iC1), 29071, Málaga, Spain.
| |
Collapse
|
3
|
Tavari T, Meamardoost S, Sepehry N, Akbarzadeh P, Nazari M, Hashemi NN, Nazari M. Effects of 3D electrodes arrangement in a novel AC electroosmotic micropump: Numerical modeling and experimental validation. Electrophoresis 2023; 44:450-461. [PMID: 36448415 DOI: 10.1002/elps.202200215] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Revised: 11/07/2022] [Accepted: 11/16/2022] [Indexed: 12/03/2022]
Abstract
To date, a comprehensive systematic optimization framework, capable of accurately predicting an efficient electrode geometry, is not available. Here, different geometries, including 3D step electrodes, have been designed in order to fabricate AC electroosmosis micropumps. It is essential to optimize both geometrical parameters of electrode, such as width and height of steps on each base electrode and their location in one pair, the size of each base electrode (symmetric or asymmetric), the gap of electrode pairs, and nongeometrical parameters such as fluid flow in a channel and electrical characteristics (e.g., frequency and voltage). The governing equations comprising of electric domain and fluid domain have been coupled using finite element method. The developed model was employed to investigate the effect of electrode geometric parameters on electroosmotic slip velocity and its subsequent effect on pressure and flow rate. Numerical simulation indicates that the optimal performance can be achieved using a design with varying step height and displacement, at a given voltage (2.5 V) and frequency (1 kHz). Finally, in order to validate the numerical simulation, the optimal microchip was fabricated using a combination of photolithography, electroplating, and a polydimethylsiloxane microchannel. Our results indicate that our micropump is capable of generating a pressure, velocity, and flow rate of 74.2 Pa, 1.76 mm/s, and 14.8 µl/min, respectively. This result reveals that our proposed geometry outperforms the state-of-the-art micropumps previously reported in the literature by improving the fluid velocity by 32%, with 80% less electrodes per unit length, and whereas the channel length is ∼80% shorter.
Collapse
Affiliation(s)
- Tannaz Tavari
- Department of Mechanical and Mechatronics Engineering, Shahrood University of Technology, Shahrood, Iran
| | - Saber Meamardoost
- Department of Chemical and Biological Engineering, University at Buffalo, Buffalo, New York, USA
| | - Naserodin Sepehry
- Department of Mechanical and Mechatronics Engineering, Shahrood University of Technology, Shahrood, Iran
| | - Pooria Akbarzadeh
- Department of Mechanical and Mechatronics Engineering, Shahrood University of Technology, Shahrood, Iran
| | - Mostafa Nazari
- Department of Mechanical and Mechatronics Engineering, Shahrood University of Technology, Shahrood, Iran
| | - Nicole N Hashemi
- Department of Mechanical Engineering, Iowa State University, Ames, Iowa, USA
| | - Mohsen Nazari
- Department of Mechanical and Mechatronics Engineering, Shahrood University of Technology, Shahrood, Iran
| |
Collapse
|
4
|
Tavari T, Nazari M, Meamardoost S, Tamayol A, Samandari M. A systematic overview of electrode configuration in electric‐driven micropumps. Electrophoresis 2022; 43:1476-1520. [DOI: 10.1002/elps.202100317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Revised: 02/18/2022] [Accepted: 03/22/2022] [Indexed: 11/07/2022]
Affiliation(s)
- Tannaz Tavari
- Department of Mechanical and Mechatronics Engineering Shahrood University of Technology Shahrood Iran
| | - Mohsen Nazari
- Department of Mechanical and Mechatronics Engineering Shahrood University of Technology Shahrood Iran
| | - Saber Meamardoost
- Department of Chemical and Biological Engineering University at Buffalo Buffalo New York USA
| | - Ali Tamayol
- Department of Biomedical Engineering University of Connecticut Health Center Farmington Connecticut USA
| | - Mohamadmahdi Samandari
- Department of Biomedical Engineering University of Connecticut Health Center Farmington Connecticut USA
| |
Collapse
|
5
|
Liu W, Sun Y, Yan H, Ren Y, Song C, Wu Q. A Simulation Analysis of Nanofluidic Ion Current Rectification Using a Metal-Dielectric Janus Nanopore Driven by Induced-Charge Electrokinetic Phenomena. MICROMACHINES 2020; 11:mi11060542. [PMID: 32471139 PMCID: PMC7345169 DOI: 10.3390/mi11060542] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/07/2020] [Revised: 05/25/2020] [Accepted: 05/26/2020] [Indexed: 12/25/2022]
Abstract
We propose herein a unique mechanism of generating tunable surface charges in a metal-dielectric Janus nanopore for the development of nanofluidic ion diode, wherein an uncharged metallic nanochannel is in serial connection with a dielectric nanopore of fixed surface charge. In response to an external electric field supplied by two probes located on both sides of the asymmetric Janus nanopore, the metallic portion of the nanochannel is electrochemically polarized, so that a critical junction is formed between regions with an enriched concentration of positive and negative ions in the bulk electrolyte adjacent to the conducting wall. The combined action of the field-induced bipolar induced double layer and the native unipolar double layer full of cations within the negatively-charged dielectric nanopore leads to a voltage-controllable heterogenous volumetric charge distribution. The electrochemical transport of field-induced counterions along the nanopore length direction creates an internal zone of ion enrichment/depletion, and thereby enhancement/suppression of the resulting electric current inside the Janus nanopore for reverse working status of the nanofluidic ion diode. A mathematical model based upon continuum mechanics is established to study the feasibility of the Janus nanochannel in causing sufficient ion current rectification, and we find that only a good matching between pore diameter and Debye length is able to result in a reliable rectifying functionality for practical applications. This rectification effect is reminiscent of the typical bipolar membrane, but much more flexible on account of the nature of a voltage-based control due to induced-charge electrokinetic polarization of the conducting end, which may hold promise for osmotic energy conversion wherein an electric current appears due to a difference in salt concentration. Our theoretical demonstration of a composite metal-dielectric ion-selective medium provides useful guidelines for construction of flexible on-chip platforms utilizing induced-charge electrokinetic phenomena for a high degree of freedom ion current control.
Collapse
Affiliation(s)
- Weiyu Liu
- School of Electronics and Control Engineering, Chang’an University, Middle-Section of Nan’er Huan Road, Xi’an 710064, China; (W.L.); (Q.W.)
| | - Yongjun Sun
- School of Mechatronics Engineering, Harbin Institute of Technology, West Da-zhi Street 92, Harbin 150001, China; (Y.R.); (C.S.)
- State Key Laboratory of Robotics and System, Harbin Institute of Technology, West Da-Zhi Street 92, Harbin 150001, China
- Correspondence: (Y.S.); (H.Y.)
| | - Hui Yan
- School of Mechatronics Engineering, Harbin Institute of Technology, West Da-zhi Street 92, Harbin 150001, China; (Y.R.); (C.S.)
- Correspondence: (Y.S.); (H.Y.)
| | - Yukun Ren
- School of Mechatronics Engineering, Harbin Institute of Technology, West Da-zhi Street 92, Harbin 150001, China; (Y.R.); (C.S.)
- State Key Laboratory of Robotics and System, Harbin Institute of Technology, West Da-Zhi Street 92, Harbin 150001, China
| | - Chunlei Song
- School of Mechatronics Engineering, Harbin Institute of Technology, West Da-zhi Street 92, Harbin 150001, China; (Y.R.); (C.S.)
| | - Qisheng Wu
- School of Electronics and Control Engineering, Chang’an University, Middle-Section of Nan’er Huan Road, Xi’an 710064, China; (W.L.); (Q.W.)
| |
Collapse
|
6
|
Multifrequency Induced-Charge Electroosmosis. MICROMACHINES 2019; 10:mi10070447. [PMID: 31277290 PMCID: PMC6680487 DOI: 10.3390/mi10070447] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Revised: 06/27/2019] [Accepted: 07/01/2019] [Indexed: 01/31/2023]
Abstract
We present herein a unique concept of multifrequency induced-charge electroosmosis (MICEO) actuated directly on driving electrode arrays, for highly-efficient simultaneous transport and convective mixing of fluidic samples in microscale ducts. MICEO delicately combines transversal AC electroosmotic vortex flow, and axial traveling-wave electroosmotic pump motion under external dual-Fourier-mode AC electric fields. The synthetic flow field associated with MICEO is mathematically analyzed under thin layer limit, and the particle tracing experiment with a special powering technique validates the effectiveness of this physical phenomenon. Meanwhile, the simulation results with a full-scale 3D computation model demonstrate its robust dual-functionality in inducing fully-automated analyte transport and chaotic stirring in a straight fluidic channel embedding double-sided quarter-phase discrete electrode arrays. Our physical demonstration with multifrequency signal control on nonlinear electroosmosis provides invaluable references for innovative designs of multifunctional on-chip analytical platforms in modern microfluidic systems.
Collapse
|
7
|
Du K, Liu W, Ren Y, Jiang T, Song J, Wu Q, Tao Y. A High-Throughput Electrokinetic Micromixer via AC Field-Effect Nonlinear Electroosmosis Control in 3D Electrode Configurations. MICROMACHINES 2018; 9:E432. [PMID: 30424365 PMCID: PMC6187382 DOI: 10.3390/mi9090432] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Revised: 08/23/2018] [Accepted: 08/24/2018] [Indexed: 11/16/2022]
Abstract
In this study, we make use of the AC field-effect flow control on induced-charge electroosmosis (ICEO), to develop an electrokinetic micromixer with 3D electrode layouts, greatly enhancing the device performance compared to its 2D counterpart of coplanar metal strips. A biased AC voltage wave applied to the central gate terminal, i.e., AC field-effect control, endows flow field-effect-transistor of ICEO the capability to produce arbitrary symmetry breaking in the transverse electrokinetic vortex flow pattern, which makes it fascinating for microfluidic mixing. Using the Debye-Huckel approximation, a mathematical model is established to test the feasibility of the new device design in stirring nanoparticle samples carried by co-flowing laminar streams. The effect of various experimental parameters on constructing a viable micromixer is investigated, and an integrated microdevice with a series of gate electrode bars disposed along the centerline of the channel bottom surface is proposed for realizing high-flux mixing. Our physical demonstration on field-effect nonlinear electroosmosis control in 3D electrode configurations provides useful guidelines for electroconvective manipulation of nanoscale objects in modern microfluidic systems.
Collapse
Affiliation(s)
- Kai Du
- School of Electronics and Control Engineering, and School of Highway, Chang'an University, Middle-Section of Nan'er Huan Road, Xi'an 710064, China.
| | - Weiyu Liu
- School of Electronics and Control Engineering, and School of Highway, Chang'an University, Middle-Section of Nan'er Huan Road, Xi'an 710064, China.
| | - Yukun Ren
- State Key Laboratory of Robotics and System, Harbin Institute of Technology, West Da-zhi Street 92, Harbin 150001, China.
| | - Tianyi Jiang
- State Key Laboratory of Robotics and System, Harbin Institute of Technology, West Da-zhi Street 92, Harbin 150001, China.
| | - Jingni Song
- School of Electronics and Control Engineering, and School of Highway, Chang'an University, Middle-Section of Nan'er Huan Road, Xi'an 710064, China.
| | - Qian Wu
- Science and Technology on Reactor System Design Technology Laboratory, Nuclear Power Institute of China, Chengdu 610213, China.
| | - Ye Tao
- State Key Laboratory of Robotics and System, Harbin Institute of Technology, West Da-zhi Street 92, Harbin 150001, China.
| |
Collapse
|
8
|
Electrode Cooling Effect on Out-Of-Phase Electrothermal Streaming in Rotating Electric Fields. MICROMACHINES 2017; 8:mi8110327. [PMID: 30400517 PMCID: PMC6190253 DOI: 10.3390/mi8110327] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/23/2017] [Revised: 11/03/2017] [Accepted: 11/04/2017] [Indexed: 11/17/2022]
Abstract
In this work, we focus on investigating electrothermal flow in rotating electric fields (ROT-ETF), with primary attention paid to the horizontal traveling-wave electrothermal (TWET) vortex induced at the center of the electric field. The frequency-dependent flow profiles in the microdevice are analyzed using different heat transfer models. Accordingly, we address in particular the importance of electrode cooling in ROT-ETF as metal electrodes of high thermal conductivity, while substrate material of low heat dissipation capability is employed to develop such microfluidic chips. Under this circumstance, cooling of electrode array due to external natural convection on millimeter-scale electrode pads for external wire connection occurs and makes the internal temperature maxima shift from the electrode plane to a bit of distance right above the cross-shaped interelectrode gaps, giving rise to reversal of flow rotation from a typical repulsion-type to attraction-type induction vortex, which is in good accordance with our experimental observations of co-field TWET streaming at frequencies in the order of reciprocal charge relaxation time of the bulk fluid. These results point out a way to make a correct interpretation of out-of-phase electrothermal streaming behavior, which holds great potential for handing high-conductivity analytes in modern microfluidic systems.
Collapse
|
9
|
Li Y, Ren Y, Liu W, Chen X, Tao Y, Jiang H. On controlling the flow behavior driven by induction electrohydrodynamics in microfluidic channels. Electrophoresis 2017; 38:983-995. [DOI: 10.1002/elps.201600500] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Revised: 12/19/2016] [Accepted: 12/21/2016] [Indexed: 11/10/2022]
Affiliation(s)
- Yanbo Li
- School of Electronics and Control Engineering; Chang'an University; Xi'an Shaanxi P. R. China
| | - Yukun Ren
- School of Mechatronics Engineering; Harbin Institute of Technology; Harbin Heilongjiang P. R. China
- State Key Laboratory of Robotics and System; Harbin Institute of Technology; Harbin Heilongjiang P. R. China
| | - Weiyu Liu
- School of Electronics and Control Engineering; Chang'an University; Xi'an Shaanxi P. R. China
- School of Mechatronics Engineering; Harbin Institute of Technology; Harbin Heilongjiang P. R. China
| | - Xiaoming Chen
- School of Mechatronics Engineering; Harbin Institute of Technology; Harbin Heilongjiang P. R. China
| | - Ye Tao
- School of Mechatronics Engineering; Harbin Institute of Technology; Harbin Heilongjiang P. R. China
| | - Hongyuan Jiang
- School of Mechatronics Engineering; Harbin Institute of Technology; Harbin Heilongjiang P. R. China
- State Key Laboratory of Robotics and System; Harbin Institute of Technology; Harbin Heilongjiang P. R. China
| |
Collapse
|
10
|
García-Sánchez P, Loucaides NG, Ramos A. Pumping of electrolytes by electrical forces induced on the diffusion layer: A weakly nonlinear analysis. Phys Rev E 2017; 95:022802. [PMID: 28297906 DOI: 10.1103/physreve.95.022802] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2016] [Indexed: 06/06/2023]
Abstract
Pumping of electrolytes in microchannels can be achieved with the use of microelectrodes subjected to AC potentials. Experiments have shown an influence of Faradaic currents in the pumping performance, and theoretical studies for asymmetric electrolytes suggest that induced charges in the diffusion layer play an important role. In this work we consider the case of a diffusion layer induced by an array of electrodes subjected to a traveling wave potential and we include Faradaic currents. Previous theoretical studies considered the case of very small applied voltages, which allowed for two major simplifications: (i) Butler-Volmer (B-V) equation was linearized, and (ii) the presence of gradients in ion concentration was neglected. We extend previous results and used the full nonlinear B-V equation. A comparison with the linear limit shows that the flow rate in both cases coincides for voltages around and below ≈0.25 V. For voltages larger than this, the nonlinear equations show that gradients in ion concentration appear and have an important influence, therefore, the predictions deviate from the linear model. We show that the electrical force in the diffusion layer can induce pumping either in the same or the opposite direction of the applied traveling-wave potential and it could be responsible for the reversal of the flow as observed in experiments.
Collapse
Affiliation(s)
- Pablo García-Sánchez
- Depto. Electrónica y Electromagnetismo, Facultad de Física, Universidad de Sevilla, Avda. Reina Mercedes s/n, 41012, Sevilla, Spain
| | - Neophytos G Loucaides
- Depto. Electrónica y Electromagnetismo, Facultad de Física, Universidad de Sevilla, Avda. Reina Mercedes s/n, 41012, Sevilla, Spain
| | - Antonio Ramos
- Depto. Electrónica y Electromagnetismo, Facultad de Física, Universidad de Sevilla, Avda. Reina Mercedes s/n, 41012, Sevilla, Spain
| |
Collapse
|
11
|
Abstract
Nanoscale fluid transport through conduits in the 1-100 nm range is termed as nanofluidics. Over the past decade or so, significant scientific and technological advances have occurred in the domain of nanofluidics with a transverse external electrical signal through a dielectric layer permitting control over ionic and fluid flows in these nanoscale conduits. Consequently, this special class of nanofluidic devices is commonly referred to as field effect devices, analogous to the solid-state field effect transistors that form the basis for modern electronics. In this mini-review, we focus on summarizing the recent developments in field effect nanofluidics as a discipline and evaluate both tutorially and critically the scientific and technological advances that have been reported, including a discussion on the future outlook and identifying broad open questions which suggest that there are many breakthroughs still to come in field-effect nanofluidics.
Collapse
Affiliation(s)
- Shaurya Prakash
- Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210, USA.
| | - A T Conlisk
- Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210, USA.
| |
Collapse
|
12
|
Park S, Yossifon G. Induced-charge electrokinetics, bipolar current, and concentration polarization in a microchannel-Nafion-membrane system. Phys Rev E 2016; 93:062614. [PMID: 27415327 DOI: 10.1103/physreve.93.062614] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2014] [Indexed: 06/06/2023]
Abstract
The presence of a floating electrode array located within the depletion layer formed due to concentration polarization across a microchannel-membrane interface device may produce not only induced-charge electro-osmosis (ICEO) but also bipolar current resulting from the induced Faradaic reaction. It has been shown that there exists an optimal thickness of a thin dielectric coating that is sufficient to suppress bipolar currents but still enables ICEO vortices that stir the depletion layer, thereby affecting the system's current-voltage response. In addition, the use of alternating-current electro-osmosis by activating electrodes results in further enhancement of the fluid stirring and opens new routes for on-demand spatiotemporal control of the depletion layer length.
Collapse
Affiliation(s)
- Sinwook Park
- Micro- and Nanofluidics Laboratory, Faculty of Mechanical Engineering, Technion-Israel Institute of Technology, Technion City 32000, Israel
| | - Gilad Yossifon
- Micro- and Nanofluidics Laboratory, Faculty of Mechanical Engineering, Technion-Israel Institute of Technology, Technion City 32000, Israel
| |
Collapse
|
13
|
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.
Collapse
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
| |
Collapse
|
14
|
An R, Wipf DO, Minerick AR. Spatially variant red blood cell crenation in alternating current non-uniform fields. BIOMICROFLUIDICS 2014; 8:021803. [PMID: 24753734 PMCID: PMC3977840 DOI: 10.1063/1.4867557] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Accepted: 02/24/2014] [Indexed: 05/04/2023]
Abstract
Alternating-current (AC) electrokinetics involve the movement and behaviors of particles or cells. Many applications, including dielectrophoretic manipulations, are dependent upon charge interactions between the cell or particle and the surrounding medium. Medium concentrations are traditionally treated as spatially uniform in both theoretical models and experiments. Human red blood cells (RBCs) are observed to crenate, or shrink due to changing osmotic pressure, over 10 min experiments in non-uniform AC electric fields. Cell crenation magnitude is examined as functions of frequency from 250 kHz to 1 MHz and potential from 10 Vpp to 17.5 Vpp over a 100 μm perpendicular electrode gap. Experimental results show higher peak to peak potential and lower frequency lead to greater cell volume crenation up to a maximum volume loss of 20%. A series of experiments are conducted to elucidate the physical mechanisms behind the red blood cell crenation. Non-uniform and uniform electrode systems as well as high and low ion concentration experiments are compared and illustrate that AC electroporation, system temperature, rapid temperature changes, medium pH, electrode reactions, and convection do not account for the crenation behaviors observed. AC electroosmotic was found to be negligible at these conditions and AC electrothermal fluid flows were found to reduce RBC crenation behaviors. These cell deformations were attributed to medium hypertonicity induced by ion concentration gradients in the spatially nonuniform AC electric fields.
Collapse
Affiliation(s)
- Ran An
- 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
| |
Collapse
|
15
|
Wang J, Wei MT, Cohen JA, Ou-Yang HD. Mapping alternating current electroosmotic flow at the dielectrophoresis crossover frequency of a colloidal probe. Electrophoresis 2014; 34:1915-21. [PMID: 23616351 DOI: 10.1002/elps.201200614] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2012] [Revised: 03/23/2013] [Accepted: 03/25/2013] [Indexed: 11/08/2022]
Abstract
AC electroosmotic (ACEO) flow above the gap between coplanar electrodes is mapped by the measurement of Stokes forces on an optically trapped polystyrene colloidal particle. E²-dependent forces on the probe particle are selected by amplitude modulation (AM) of the ACEO electric field (E) and lock-in detection at twice the AM frequency. E²-dependent DEP of the probe is eliminated by driving the ACEO at the probe's DEP crossover frequency. The location-independent DEP crossover frequency is determined, in a separate experiment, as the limiting frequency of zero horizontal force as the probe is moved toward the midpoint between the electrodes. The ACEO velocity field, uncoupled from probe DEP effects, was mapped in the region 1-9 μm above a 28 μm gap between the electrodes. By use of variously sized probes, each at its DEP crossover frequency, the frequency dependence of the ACEO flow was determined at a point 3 μm above the electrode gap and 4 μm from an electrode tip. At this location the ACEO flow was maximal at ∼117 kHz for a low salt solution. This optical trapping method, by eliminating DEP forces on the probe, provides unambiguous mapping of the ACEO velocity field.
Collapse
Affiliation(s)
- Jingyu Wang
- Department of Physics, Lehigh University, Bethlehem, PA, USA
| | | | | | | |
Collapse
|
16
|
Ng WY, Ramos A, Lam YC, Wijaya IPM, Rodriguez I. DC-biased AC-electrokinetics: a conductivity gradient driven fluid flow. LAB ON A CHIP 2011; 11:4241-7. [PMID: 22052533 DOI: 10.1039/c1lc20495e] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
This paper studies the principles of fluid flow manipulation based on DC-biased AC-electrokinetics. This method makes use of planar parallel electrodes in a microfluidic channel in contact with an electrolyte solution, with a DC biased AC electrical signal applied to the electrode pair. Due to the application of DC bias, incipient Faradaic electrolytic reactions take place resulting in an increase of the ionic content of the bulk solution. The ionic content was found to be dissimilar at the cathodic and anodic sides of the channel and a conductivity difference of approximately 10% was measured for 2 V(DC). Fluid flow is generated by the action of the DC biased AC electric signal acting on the transverse conductivity gradient generated across the microchannel. The induced flow in the form of vortex was characterized experimentally and the results substantiated theoretically. The velocity of the induced flow vortex under the employed experimental conditions was ~600 to 700 μm s(-1) which is faster than those obtained in conventional AC-electroosmosis and AC-electrothermal types of flows.
Collapse
Affiliation(s)
- Wee Yang Ng
- Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), 3 Research Link, Singapore, 117602, Singapore
| | | | | | | | | |
Collapse
|
17
|
|
18
|
García-Sánchez P, Ramos A, González A. Effects of Faradaic currents on AC electroosmotic flows with coplanar symmetric electrodes. Colloids Surf A Physicochem Eng Asp 2011. [DOI: 10.1016/j.colsurfa.2010.11.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
|
19
|
Pascall AJ, Squires TM. An automated, high-throughput experimental system for induced charge electrokinetics. LAB ON A CHIP 2010; 10:2350-2357. [PMID: 20694256 DOI: 10.1039/c004926c] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Recent experiments in induced charge electrokinetics (ICEK) have shown that the standard theory generally overpredicts experimentally observed velocities. Such discrepancies reduce the efficacy of practical ICEK devices, and highlight our incomplete understanding of electrokinetic phenomena. Here, we present an automated experimental system that allows for the rapid collection of ICEK data under a variety of conditions ( approximately 1000 per day) to help develop and constrain new theories. We demonstrate this system by studying the ICEK slip flows over electrodes that have been controllably "contaminated" with a dielectric layer, either SiO(2) or an alkanethiol self-assembled monolayer, of known thickness. We also develop a theory that accounts for the effects of the dielectric coatings surface chemistry that yields quantitative agreement with experiments over nearly a thousand distinct conditions in the SiO(2) system and present an additional three thousand experiments of flows over alkanethiol monolayers. Our experimental system allows the direct interrogation of the physico-chemical effects that influence ICEK flows and for the optimization of these flows in lab-on-a-chip systems.
Collapse
Affiliation(s)
- Andrew J Pascall
- Department of Chemical Engineering, University of California, Santa Barbara, USA
| | | |
Collapse
|
20
|
Henning A, Bier FF, Hölzel R. Dielectrophoresis of DNA: Quantification by impedance measurements. BIOMICROFLUIDICS 2010; 4:022803. [PMID: 20697597 PMCID: PMC2917884 DOI: 10.1063/1.3430550] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2010] [Accepted: 04/27/2010] [Indexed: 05/12/2023]
Abstract
Dielectrophoretic properties of DNA have been determined by measuring capacitance changes between planar microelectrodes. DNA sizes ranged from 100 bp to 48 kbp, DNA concentrations from below 0.1 to 70 mugml. Dielectrophoretic spectra exhibited maximum response around 3 kHz and 3 MHz. The strongest response was found for very long DNA (above 10 kbp) and for short 100 bp fragments, which corresponds to the persistence length of DNA. The method allows for an uncomplicated, automatic acquisition of the dielectrophoretic properties of submicroscopical objects without the need for labeling protocols or optical accessibility.
Collapse
Affiliation(s)
- Anja Henning
- Fraunhofer Institute for Biomedical Engineering, D-14476 Potsdam, Germany
| | | | | |
Collapse
|
21
|
|
22
|
Huang CC, Bazant MZ, Thorsen T. Ultrafast high-pressure AC electro-osmotic pumps for portable biomedical microfluidics. LAB ON A CHIP 2010; 10:80-5. [PMID: 20024054 DOI: 10.1039/b915979g] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
This paper details the development of an integrated AC electro-osmotic (ACEO) microfluidic pump for dilute electrolytes consisting of a long serpentine microchannel lined with three dimensional (3D) stepped electrode arrays. Using low AC voltage (1 V rms, 1 kHz), power (5 mW) and current (4.5 mA) in water, the pump is capable of generating a 1.3 kPa head pressure, a 100-fold increase over prior ACEO pumps, and a 1.3 mm/s effective slip velocity over the electrodes without flow reversal. The integrated ACEO pump can utilize low ionic strength solutions such as distilled water as the working solution to pump physiological strength (100 mM) biological solutions in separate microfluidic devices, with potential applications in portable or implantable biomedical microfluidic devices. As a proof-of-concept experiment, the use of the ACEO pumps for DNA hybridization in a microfluidic microarray is demonstrated.
Collapse
Affiliation(s)
- Chien-Chih Huang
- Institute for Soldier Nanotechnologies, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | | | | |
Collapse
|
23
|
González A, Ramos A, García-Sánchez P, Castellanos A. Effect of the combined action of Faradaic currents and mobility differences in ac electro-osmosis. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 81:016320. [PMID: 20365473 DOI: 10.1103/physreve.81.016320] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2009] [Indexed: 05/29/2023]
Abstract
In this work, we extend previous analyses of ac electro-osmosis to account for the combined action of two experimentally relevant effects: (i) Faradaic currents from electrochemical reactions at the electrodes and (ii) differences in ion mobilities of the electrolyte. In previous works, the ac electro-osmotic motion has been analyzed theoretically under the assumption that only forces in the diffuse (Debye) layer are relevant. Here, we first show that if the ion mobilities of a 1-1 aqueous solution are different, the charged zone expands from the Debye layer to include the diffusion layer. We later include the Faradaic currents and, as an attempt to explore both factors simultaneously, we perform a thin-layer, low-frequency, linear analysis of the system. Finally, the model is applied to the case of an electrolyte actuated by a traveling-wave signal. A steady liquid motion in opposite direction to the applied signal is predicted for some ranges of the parameters. This could serve as a partial explanation for the observed flow reversal in some experiments.
Collapse
Affiliation(s)
- A González
- Departamento Física Aplicada III, Universidad de Sevilla, Sevilla, Spain.
| | | | | | | |
Collapse
|
24
|
Towards an understanding of induced-charge electrokinetics at large applied voltages in concentrated solutions. Adv Colloid Interface Sci 2009; 152:48-88. [PMID: 19879552 DOI: 10.1016/j.cis.2009.10.001] [Citation(s) in RCA: 427] [Impact Index Per Article: 28.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2009] [Revised: 09/29/2009] [Accepted: 10/01/2009] [Indexed: 11/22/2022]
Abstract
The venerable theory of electrokinetic phenomena rests on the hypothesis of a dilute solution of point-like ions in quasi-equilibrium with a weakly charged surface, whose potential relative to the bulk is of order the thermal voltage (kT/e approximately 25 mV at room temperature). In nonlinear electrokinetic phenomena, such as AC or induced-charge electro-osmosis (ACEO, ICEO) and induced-charge electrophoresis (ICEP), several V approximately 100 kT/e are applied to polarizable surfaces in microscopic geometries, and the resulting electric fields and induced surface charges are large enough to violate the assumptions of the classical theory. In this article, we review the experimental and theoretical literatures, highlight discrepancies between theory and experiment, introduce possible modifications of the theory, and analyze their consequences. We argue that, in response to a large applied voltage, the "compact layer" and "shear plane" effectively advance into the liquid, due to the crowding of counterions. Using simple continuum models, we predict two general trends at large voltages: (i) ionic crowding against a blocking surface expands the diffuse double layer and thus decreases its differential capacitance, and (ii) a charge-induced viscosity increase near the surface reduces the electro-osmotic mobility; each trend is enhanced by dielectric saturation. The first effect is able to predict high-frequency flow reversal in ACEO pumps, while the second may explain the decay of ICEO flow with increasing salt concentration. Through several colloidal examples, such as ICEP of an uncharged metal sphere in an asymmetric electrolyte, we show that nonlinear electrokinetic phenomena are generally ion-specific. Similar theoretical issues arise in nanofluidics (due to confinement) and ionic liquids (due to the lack of solvent), so the paper concludes with a general framework of modified electrokinetic equations for finite-sized ions.
Collapse
|
25
|
Squires TM. Induced-charge electrokinetics: fundamental challenges and opportunities. LAB ON A CHIP 2009; 9:2477-83. [PMID: 19680573 DOI: 10.1039/b906909g] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Induced-charge electrokinetic (ICEK) phenomena occur when an applied electric field induces an ionic double-layer over a polarizable surface, then forces that induced double-layer into electro-osmotic flow. The nonlinear character of ICEK phenomena enable steady flows to be driven using small AC potentials, which in turn reduces or eliminates electrochemical reactions. As such, ICEK holds promise as a mechanism by which low-voltage, high-pressure pumps may be developed to enable portable, self-contained microfluidic manipulation. Here we review the basic physics of induced-charge electrokinetic phenomena and the advantages they hold for Lab-on-a-Chip devices, in addition to the opportunities they present for fundamental science. In particular, these systems are unique in that all aspects of the (measurable) ICEK flows can be predicted in advance using standard electrokinetic theories, which can then be compared with experimental data. Such comparisons have revealed a number of striking discrepancies between theory and experiment, thus indicating the standard model is missing key physical or chemical ingredients. We discuss specific discrepancies-which remain to be understood-and the challenges they pose for widespread implementation of ICEK in practical Lab-on-a-Chip devices. We propose and present a variety of challenges and opportunities-theoretical and experimental, fundamental and applied-which must be addressed.
Collapse
Affiliation(s)
- Todd M Squires
- Department of Chemical Engineering, University of California, Santa Barbara, CA 93106-5080, USA
| |
Collapse
|
26
|
García-Sánchez P, Ramos A, González A, Green NG, Morgan H. Flow reversal in traveling-wave electrokinetics: an analysis of forces due to ionic concentration gradients. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:4988-97. [PMID: 19320476 DOI: 10.1021/la803651e] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Pumping of electrolytes using ac electric fields from arrays of microelectrodes is a subject of current research. The behavior of fluids at low signal amplitudes (<2-3 V(pp)) is in qualitative agreement with the prediction of the ac electroosmosis theory. At higher voltages, this theory cannot account for the experimental observations. In some cases, net pumping is generated in the direction opposite to that predicted by the theory (flow reversal). In this work, we use fluorescent dyes to study the effect of ionic concentration gradients generated by Faradaic currents. We also evaluate the influence of factors such as the channel height and microelectrode array shape in the pumping of electrolytes with traveling-wave potentials. Induced charge beyond the Debye length is postulated to be responsible for the forces generating the observed flows at higher voltages. Numerical calculations are performed in order to illustrate the mechanisms that might be responsible for generating the flow.
Collapse
Affiliation(s)
- P García-Sánchez
- Departamento de Electronica y Electromagnetismo, Facultad de Fisica, Universidad de Sevilla, 41012, Seville, Spain.
| | | | | | | | | |
Collapse
|
27
|
Ng WY, Lam YC, Rodríguez I. Experimental verification of Faradaic charging in ac electrokinetics. BIOMICROFLUIDICS 2009; 3:22405. [PMID: 19693340 PMCID: PMC2717573 DOI: 10.1063/1.3120273] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2009] [Accepted: 03/21/2009] [Indexed: 05/06/2023]
Abstract
This paper investigates the phenomenon of Faradaic charging in ac electrokinetics. Faradaic reactions were suggested as a key effect responsible for the reversal of pumping direction in ac micropumps. However, this hypothesis has yet to be proven convincingly and directly. Here we present an ion detection strategy to determine the production of ions through Faradaic hydrolytic reactions originating from direct application of voltage to electrolytic solutions during ac electrokinetics. Experiments were performed with symmetrical planar electrodes aligned along a microfluidic channel. Fluorescein, a pH-dependent dye, was employed as the pH indicator for the detection of ion production. Images were captured for analysis at various voltage levels. From analyzing the fluorescence intensity and its distribution, it can be concluded that the production of ions from hydrolytic reactions takes place and increases with the ac voltage. The coefficient of deviation indicates a significant enhancement at ac voltage above 11 V(pp). Lastly, we demonstrate a strategy using dc-biased ac electrokinetics to achieve controllability in direction and magnitude of the net fluid flow in pumping application.
Collapse
|
28
|
Ng WY, Goh S, Lam YC, Yang C, Rodríguez I. DC-biased AC-electroosmotic and AC-electrothermal flow mixing in microchannels. LAB ON A CHIP 2009; 9:802-9. [PMID: 19255662 DOI: 10.1039/b813639d] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
This paper presents a novel approach of mixing two laminar flowing streams in microchannels. The mixer consists of a pair of electrodes disposed along a fluidic channel. By energizing the electrodes with a DC-biased (2.5 V) AC voltage (20 Vpp), an electrokinetic flow is induced with a flow profile perpendicular to that of the incoming laminar streams of liquids to be mixed. As a result, the flow lines of the incoming streams and the induced flow are forced to crossover and very efficient stirring and mixing at short mixing length can be achieved. The mixer can be operated from the AC-electroosmotic (ACEO) (sigma=1 mS/m, f=100 kHz) to the AC-electrothermal (ACET) (sigma=500 mS/m, f=500 kHz) flow regimes. The mixing efficiency in the ACEO regime was 92%, with a mixing length of 600 microm (Q=2 microL/min), an estimated mixing time of 69 ms and an induced ACEO flow velocity of approximately 725 microm/s. The mixing efficiency in the ACET regime was 65% for a mixing length of approximately 1200 microm. The mixer is efficient and suitable for mixing reagents in a fluid media from low to high conductivity as required in diverse microfluidic applications.
Collapse
Affiliation(s)
- Wee Yang Ng
- Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), 3 Research Link, Singapore 117602
| | | | | | | | | |
Collapse
|