Two simple and rugged designs for creating microfluidic sheath flow

Abstract

A simple design capable of 2-dimensional hydrodynamic focusing is proposed and successfully demonstrated. In the past, most microfluidic sheath flow systems have often only confined the sample solution on the sides, leaving the top and bottom of the sample stream in contact with the floor and ceiling of the channel. While relatively simple to build, these designs increase the risk of adsorption of sample components to the top and bottom of the channel. A few designs have been successful in completely sheathing the sample stream, but these typically require multiple sheath inputs and several alignment steps. In the designs presented here, full sheathing is accomplished using as few as one sheath input, which eliminates the need to carefully balance the flow of two or more sheath inlets. The design is easily manufactured using current microfabrication techniques. Furthermore, the sample and sheath fluid can be subsequently separated for recapture of the sample fluid or re-use of the sheath fluid. Designs were demonstrated in poly(dimethylsiloxane) (PDMS) using soft lithography and poly(methyl methacrylate) (PMMA) using micromilling and laser ablation.

Engineering fluid flow using sequenced microstructures

“…Additionally, engineering a variety of cross-sectional lens shapes with a fluid of separate index of refraction 29 can be of use for opto-fluidic control and sensing 30 . Rotating or moving fluid streams to be analysed away from walls to regions of uniform downstream velocity at the channel centre can minimize Taylor dispersion 9 , bring fluid into a small focal spot for optical interrogation 31,32 or reduce fouling and adhesion to channel surfaces. Conversely, bringing fluid to narrow slow moving regions near channel walls can enhance surface reactions (for example, immunoassays 33 ), or aid in affinity capture of cells 34 or molecules.…”

Microfluidic sorting of microtissues

“…To further improve sorting efficiencies of this design, 3D focusing could be implemented to more precisely control particle position in the channel and thereby particle velocities. 32 An additional important consideration for implementation of the devices reported here is the design of software that is capable of defining a positive event based on an optical input. One or more signals must be relayed to a DAQ card to execute a given sorting event.…”

Review Article: Recent advancements in optofluidic flow cytometer

“…They developed a microfluidic flow cytometer in which the sample fluid was thus confined to a small volume ͑20ϫ 34ϫ 30 m 3 ͒ to reduce variations in detection signal intensities. 26 Similarly, Lee et al 27 used a contraction-expansion array microchannel ͓Fig. 3͑b͔͒ to achieve threedimensional flow focusing in a single-layer device.…”