Hydrodynamic focusing of conducting fluids for conductivity-based biosensors

Nasir, Mansoor; Ateya, Daniel A.; Burk, D.; Golden, Joel P.; Ligler, Frances S.

doi:10.1016/j.bios.2009.10.033

Cited by 28 publications

(19 citation statements)

References 25 publications

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“…Parallel laminar flow of two or more liquid streams in microchannels has been studied extensively over the past decade for use in microfluidic and biomedical applications such as controlling flow paths (Atencia and Beebe 2005;Lee et al 2006;Walsh et al 2007), patterning of surfaces (Kenis et al 1999), diffusional sensors (Brody et al 1996;Hatch et al 2001), flow cytometry on a chip Huh et al 2005;Simonnet and Groisman 2006), and impedance spectroscopy (Hua and Pennell 2009;Nasir et al 2009). In many of these devices, one or multiple streams focus another stream by influencing its fluidic path.…”

Section: Introductionmentioning

confidence: 99%

Parameters affecting the shape of a hydrodynamically focused stream

Nasir

Mott

Kennedy

et al. 2011

Microfluid Nanofluid

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Even at low Reynolds numbers, momentum can impact the shape of hydrodynamically focused flow. Both theoretical and experimental characterization of hydrodynamic focusing in microchannels at Reynolds numbers B25 revealed the important parameters that affect the shape of the focused layer. A series of symmetric and asymmetric microfluidic channels with two converging streams were fabricated with different angles of confluence at the junction. The channels were used to study the characteristics of Y-type microchannels for flow-focusing. Computational analysis and experimental results gathered using confocal microscopy and particle image velocimetry indicated that the orientation of the sheath and the sample stream inlets, as well as the absolute flow velocities, determine the curvature in the concentration distribution of the focused stream. Decreasing the angle of confluence between sheath and sample, as well as reducing the overall Reynolds number, resulted in a flat interface between sheath and focused fluids. Alignment of the faster flowing sheath fluid channel with the main channel also reduced the inertial effects and produced a focused stream with a flat concentration profile. Control over the shape of the focused stream is important in many biosensors and lab-on-a-chip devices that rely on hydrodynamic focusing for increased detection sensitivity.

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Section: Introductionmentioning

confidence: 99%

Parameters affecting the shape of a hydrodynamically focused stream

Nasir

Mott

Kennedy

et al. 2011

Microfluid Nanofluid

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“…In essence, a virtual microchannel with pliable boundaries is created as a result of focusing the flow of the conducting fluid within the physical confines of the larger microfluidic channel. The ability to detect immobilized magnetic beads [10] and antibody-bound bacteria[21] has been demonstrated using hydrodynamic focusing in a four-electrode impedance-based microfluidic device.…”

Section: Hydrodynamic Focusing For Impedance-based Microfluidic Biosementioning

confidence: 99%

“…Initially, Nasir and colleagues proposed a simple two-inlet T-junction design, where the focusing fluid inlet was perpendicular to both the conducting fluid inlet and the main microchannel containing coplanar electrodes for impedance measurements [10]. The result of this design was a focused stream with a U-shaped cross-sectional profile with cusps at the edges of the main channel (Figure 1).…”

Section: Hydrodynamic Focusing For Impedance-based Microfluidic Biosementioning

confidence: 99%

“…Re numbers were calculated based on the channel dimensions and the flow rates. Numbers in the top right of each image indicate the flow rates for the focusing and focused streams in µL/min [10]…”

Section: Figurementioning

confidence: 99%

“…Clearly, inertial forces impacted the position of one stream relative to another as the two streams passed through a Dean vortex at Re >100 [8]. However, we recently demonstrated unequivocally that the momentum of a focusing flow introduced into a microchannel at an angle perpendicular to the focused flow deformed the interface between the two streams at Re between 1 and 50 [9,10]. Several techniques have evolved that control the shape of the focused stream, whether to prevent unintentional deviations from a flat interface or to create a fluidic interface with a specific geometric profile.…”

Section: Introductionmentioning

confidence: 99%

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Hydrodynamic focusing—a versatile tool

et al. 2011

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The control of hydrodynamic focusing in a microchannel has inspired new approaches for microfluidic mixing, separations, sensors, cell analysis and microfabrication. Achieving a flat interface between the focusing and focused fluids is dependent on Reynolds number and device geometry, and many hydrodynamic focusing systems can benefit from this understanding. For applications where a specific cross-sectional shape is desired for the focused flow, advection generated by grooved structures in the channel walls can be used to define the shape of the focused flow. Relative flow rates of the focused flow and focusing streams can be manipulated to control the crosssectional area of the focused flows. This manuscript discusses the principles for defining the shape of the interface between the focused and focusing fluids and provides examples from our lab that use hydrodynamic focusing for impedance-based sensors, flow cytometry, and microfabrication to illustrate the breadth of opportunities for introducing new capabilities into microfluidic systems. We evaluate each example for the advantages and limitations integral to utilization of hydrodynamic focusing for that particular application.

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Hydrodynamic and electrical considerations in the design of a four-electrode impedance-based microfluidic device

2011

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A four-electrode impedance-based microfluidic device has been designed with tunable sensitivity for future applications to the detection of pathogens and functionalized microparticles specifically bound to molecular recognition molecules on the surface of a microfluidic channel. In order to achieve tunable sensitivity, hydrodynamic focusing was employed to confine the electric current by simultaneous introduction of two fluids (high- and low-conductivity solutions) into a microchannel at variable flow-rate ratios. By increasing the volumetric flow rate of the low-conductivity solution (sheath fluid) relative to the high-conductivity solution (sample fluid), increased focusing of the high-conductivity solution over four coplanar electrodes was achieved, thereby confining the current during impedance interrogation. The hydrodynamic and electrical properties of the device were analyzed for optimization and to resolve issues that would impact sensitivity and reproducibility in subsequent biosensor applications. These include variability in the relative flow rates of the sheath and sample fluids, changes in microchannel dimensions, and ionic concentration of the sample fluid. A comparative analysis of impedance measurements using four-electrode versus two-electrode configurations for impedance measurements also highlighted the advantages of using four electrodes for portable sensor applications.

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Hydrodynamic focusing of conducting fluids for conductivity-based biosensors

Cited by 28 publications

References 25 publications

Parameters affecting the shape of a hydrodynamically focused stream

Parameters affecting the shape of a hydrodynamically focused stream

Hydrodynamic focusing—a versatile tool

Hydrodynamic and electrical considerations in the design of a four-electrode impedance-based microfluidic device

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