Three-Dimensional Hydrodynamic Focusing in Polydimethylsiloxane (PDMS) Microchannels

Abstract

This paper presents a generalization of the hydrodynamic focusing technique to three-dimensions. Three-dimensional (3-D) hydrodynamic focusing offers the advantages of precision positioning of molecules in both vertical and lateral dimensions and minimizing the interaction of the sample fluid with the surfaces of the channel walls. In an ideal approach, 3-D hydrodynamic focusing could be achieved by completely surrounding the sample flow by a cylindrical sheath flow that constrains the sample flow to the center of the channel in both the lateral and the vertical dimensions. We present here design and simulation, 3-D fabrication, and experimental results from a piecewise approximation to such a cylindrical flow. Two-dimensional (2-D) and 3-D hydrodynamic focusing chips were fabricated using micromolding methods with polydimethylsiloxane (PDMS). Three-dimensional hydrodynamic focusing chips were fabricated using the "membrane sandwich" method. Laser scanning confocal microscopy was used to study the hydrodynamic focusing experiments performed in the 2-D and 3-D chips with Rhodamine 6G solution as the sample fluid and water as the sheath fluid.[1027]

Two simple and rugged designs for creating microfluidic sheath flow

“…26,[28][29][30][31][32] Typically, two additional input channels focus the stream vertically as well as horizontally. From the standpoint of cytometry, this is a far better situation, because the sample is now completely isolated from the channel surface, and the position of the particles to be analyzed is fixed.…”

Sandwich mixer–reactor: influence of the diffusion coefficient and flow rate ratios

“…Sundararajan et al presented a generalisation of this conventional two-dimensional (2D) hydrodynamic focusing to a three-dimensional (3D) one that offers the advantage to focus the sample flow in both horizontal and vertical direction to get the sample at the centre of the channel. 25 More recently, a novel fluid manipulation technique so-called ''Microfluidic drifting'' 26 was presented with two focusing steps combined with a channel curvature resulting in a 3D hydrodynamically focused flow in the centre of the microfluidic channel. While the 2D and 3D hydrodynamic focusing are based on the focusing of the sample to mix in a thin layer at the microchannel centre, we propose here to study a sandwich mixer design with three flows of equal width.…”

3D focusing of nanoparticles in microfluidic channels

“…One example of a particularly important application is the development of a flow cytometer on a chip [1][2][3][4][5][6][7][8][9][10]. For such systems to work efficiently, it is important to be able to confine the sample into a small, spatially well-defined volume, giving as small a probe volume as possible for the detector.…”

“…8,9]. However, this technique has drawbacks: focusing is relatively easy to achieve in one dimension, but complex fabrication schemes are required to achieve two-dimensional focusing [6,7]. For this to work, very accurate control of flow rates is required, and since this type of focusing acts on the fluid rather than the particles, small particles and molecules can diffuse from the sample stream into the sheath.…”

“…The concept of DEP is particularly attractive as it enables non-contact manipulation of particles such as cells in solution by high frequency electric fields [3], and characterisation of their passive dielectric properties [4][5][6][7][8]. If 3D electrode arrays are employed, interaction with walls or unspecific adsorption of particles may be avoided.…”