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Research Papers: Multiphase Flows

# Towards New Methodologies for Manipulation of Colloidal Particles in a Miniaturized Fluidic Device: Optoelectrokinetic Manipulation Technique

[+] Author and Article Information
Jae-Sung Kwon

Mem. ASME e-mail: kwon30@purdue.edu

Steven T. Wereley

Mem. ASME
e-mail: wereley@purdue.edu
School of Mechanical Engineering and Birck Nanotechnology Center,
West Lafayette, IN 47907

References cited in the table are [1,2,4-2,4-8,10-24,27-28,30,32-8,10–24,27,28,30,32–41].

1Corresponding author.

Manuscript received August 9, 2012; final manuscript received December 12, 2012; published online March 19, 2013. Assoc. Editor: David Sinton.

J. Fluids Eng 135(2), 021306 (Mar 19, 2013) (10 pages) Paper No: FE-12-1379; doi: 10.1115/1.4023451 History: Received August 09, 2012; Revised December 12, 2012

## Abstract

The rapid electrokinetic patterning (REP) technique developed recently is a hybrid optoelectrokinetic one that manipulates micro- or nanocolloids in a microfluidic chip using the simultaneous application of a uniform ac electric field and laser illumination. Since its invention, the technique has been applied to many research fields with promising potential, but these applications are still in their early stages. In order to effectively complete and leverage the applications, this paper reviews the publications concerning the REP technique and discusses its underlying principles, applications, and future prospects.

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## Figures

Fig. 1

REP-based particle manipulations. (a) REP-based aggregation. The applied electrical signal and laser power is 7.5 kHz, 8.3 Vpp, and 20 mW, respectively. (b) REP-based patterning using multiple laser illuminations. The electric field of 4.6 kHz and 3.8 Vpp was applied and the laser power of 40 mW was supplied to the chip. (c) REP-based trapping in the continuous flow of a suspending medium. The applied electrical signal and laser power is 5.0 kHz, 10.5 Vpp, and 40 mW, respectively. (d) REP-based patterning using a “L”-shaped laser illumination. The applied electric field is 1.6 kHz and 2.0 Vpp, and the laser power is 20 mW. (e) and (f) REP-based translation. It was achieved by moving a laser illumination under a uniform electric field. The electric signal of 1.6 kHz and 2.0 Vpp and the laser of 20 mW were applied to the chip. (c)–(f) Williams et al. Reproduced with permission of the Royal Society of Chemistry [30].

Fig. 2

Hybrid characteristic of REP technique. Each figure consists of a schematic and an experimental image to describe and demonstrate the REP nature. The used particles are 1 μm polystyrene beads. (a) Particle aggregation caused by the simultaneous application of a uniform ac electric field and a laser illumination. (b) Irregular configuration of particles appearing when only the laser is turned off during the REP process. (c) Convecting away of particles occurring when only the electric field is deactivated during the REP process. Reprinted with permission from Kwon et al. Springer Science + Business Media [35].

Fig. 3

(a) Temperature gradient ( °C) on an ITO electrode surface generated by a 1064 nm near-infrared laser. Applied laser power is 150 mW and the focus of the laser is positioned at the origin [0,0]. Reprinted with permission from Kumar et al. Copyright 2010 American Chemical Society [24]. (b) Visualization of a toroidal-shaped electrothermal flow by a three-dimensional wave-front deformation particle tracking velocimetry (PTV) technique. Reprinted with permission from Kumar et al. Springer Science + Business Media [45].

Fig. 4

Physical description of REP technique. (a) Various forces exerted on particles in REP-based aggregation. Fparticle-particle and Fparticle-electrode denote the electrokinetic forces existing between particles, and between the particles and an electrode, respectively. FEHDlateral and FEHDvertical are the attractive electrohydrodynamic forces locally gathering particles each other onto the electrode. FETlateral and FETvertical are the electrothermal drag force transporting particles toward the illumination region across the electrode surface. (b) Dependence of a critical ac frequency on particle size for special case of constant surface charges (fc~1/d2). The critical frequency is defined as the minimum ac frequency where particles cannot be manipulated by REP anymore. Reproduced with permission from Kumar et al. Copyright 2010 American Chemical Society [24].

Fig. 5

Microfluidic setup for realization of rapid electrokinetic patterning (REP) technique. The chip consists of microfluidic chambers sandwiched between two parallel-plate electrodes. The top and bottom electrodes are made from an indium tin oxide (ITO)-coated glass substrate and cover slip, and are transparent for illumination and target particle observation. During experimentation, an ac electric field is supplied from a function generator and an optical illumination is provided from a Nd:YVO4 laser (λ ∼064 nm). Kwon et al. Reproduced with permission of the Royal Society of Chemistry [34].

Fig. 6

REP-based force spectroscopy. (a) Particle aggregation by REP technique. (b) Disintegration of the particle cluster by deactivation of an optical laser in REP process. (c) Measurement of the repulsive forces between the polarized particles using Delaunay triangulation method. Reprinted with permission from Kumar et al. Copyright 2010 American Chemical Society [24].

Fig. 7

Size-based sorting of like particles by REP. (a) Aggregation of 0.5, 1, and 2.0 μm polystyrene particles at 38 kHz. (b) Aggregation of 1 and 0.5 μm polystyrene particles at 80 kHz. As the frequency was increased from 38 kHz, 2.0 μm particles were separated by an electrothermal flow from the cluster. (c) Aggregation of 0.5 μm polystyrene particles at 106 kHz. The increase of the ac frequency up to 106 kHz resulted in aggregation of only 0.5 μm particles. (d) Maximum trapping frequency for different sized polystyrene particles. It shows second order polynomial fit in agreement with theory. Williams et al. Reproduced with permission of IOP publishing [32].

Fig. 8

EDL polarization-based sorting of unlike particles by REP. The unlike particles are fluorescent polystyrene and nonfluorescent silica particles of 1.0 μm in diameter. (a) Aggregation of the polystyrene beads formed by laser power of 23 mW and electric signal of 19.8 Vpp and 150 kHz. (b) Simultaneous aggregation of the two beads. When the frequency was reduced to 90 kHz, both the polystyrene and silica beads were trapped together. Williams et al. Reproduced with permission of IOP publishing [32].

Fig. 9

Manipulation of live bacteria (Shewanella Oneidensis MR-1, Saccharomyces cerevisiae, and Staphylococcus aureus) by REP technique. (a) Initialization of S. Oneidensis MR-1 bacteria assembly. (b) Patterning of S. Oneidensis MR-1 bacteria using two illumination spots in REP process. (c) and (d) Translation of S. Oneidensis MR-1 bacteria assembly across an electrode surface. (e) and (f) Size-based separation of S. cerevisiae (larger cells) and S. aureus. Kwon et al. Reproduced with permission of the Royal Society of Chemistry [34].

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