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Abstract
This work develops a microflow cytometer, based on a microfluidic chip for three-dimensional (3D) hydrodynamic focusing and a binary optical element (BOE) for shaping and homogenizing a laser beam. The microfluidic chip utilizes sheath flows to confine the sample flow along the channel centerline with a narrow cross section. In addition to hydrodynamic focusing, secondary flows are generated to strengthen the focusing in the vertical direction. In experiments, the chip was able to focus the sample flow with cross sections of 15 μm high and 8–30 μm wide at 5 m/s, under the condition of the sample flow rates between 10 and 120 μL/min. Instead of using the conventional elliptical Gaussian spot for optical detection, we used a specially designed BOE and obtained a 50 μm × 10 μm rectangular quasi-flat-top spot. The microflow cytometer combining the chip and the BOE was tested to count 3, 5, and 7 μm fluorescence microbeads, and the experimental results were comparable to or better than those derived from two commercial instruments.
Highlights
Recent advances in microfluidic technologies have brought about developments in microflow cytometers
To achieve 3D hydrodynamic focusing in a microfluidic chip, usually there is a need to manipulate multiple sheath flows independently to envelope and squeeze the sample flow in vertical and horizontal directions [17,18,19,20,21,22], followed with complicated microfluidic manifolds, flow control, and declining performance
The two sheath-flow channels are connected to the same sheath flow source, we only need to control one sheath flow and one sample flow
Summary
Recent advances in microfluidic technologies have brought about developments in microflow cytometers. To achieve 3D hydrodynamic focusing in a microfluidic chip, usually there is a need to manipulate multiple sheath flows independently to envelope and squeeze the sample flow in vertical and horizontal directions [17,18,19,20,21,22], followed with complicated microfluidic manifolds, flow control, and declining performance. To overcome these challenges, this paper establishes a 3D hydrodynamic focusing design in a microfluidic chip, comprising two sheath-flow channels and one sample-flow channel, where horizontal and vertical focusing are implemented successively. To further improve the 3D focusing, secondary flows are introduced by microstructures to vertically strengthen the focusing, and the focusing performance is comparable to conventional flow cytometers
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