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Research Papers: Techniques and Procedures

Microfluidic System for Rapid Enumeration and Detection of Microparticles

[+] Author and Article Information
A. K. Sen1

Department of Mechanical Engineering,  Indian Institute of Technology Madras, Chennai 600 036, Indiaashis@iitm.ac.in

P. Bhardwaj

Department of Mechanical Engineering,  Indian Institute of Technology Guwahati, Guwahati 781039, India

1

Corresponding author.

J. Fluids Eng 134(11), 111401 (Oct 24, 2012) (8 pages) doi:10.1115/1.4007805 History: Received February 01, 2012; Revised July 30, 2012; Published October 24, 2012

A microfluidic system for rapid concentration, enumeration, and size based detection of microparticles is presented. The system includes a micro flow cytometer chip together with fluidics, optics and control on a single platform. The micro flow cytometer chip was designed, fabricated, and integrated with fluidics and optical fibers. The flow microchannel employs chevron structures at the top and bottom surfaces of the channel to achieve two-dimensional flow focusing. The system employs a cross-flow filter for sample concentration thus enabling enumeration and detection of microparticles even at low concentration levels (∼1.1 × 104 /ml). A flow stabilizer chip based on the concept of a fluid chamber with a flexible membrane as the top wall was used to reduce flow pulsations within the fluidic system thus improving measurement accuracy. The excitation optical fiber is connected to a laser source and the collection fibers are connected to photomultiplier tubes (PMTs) for signal manipulation and conversion. Labview was used for data acquisition through a PC interface. The ability of the system for enumeration and size-based detection of microparticles was demonstrated using polystyrene microbeads suspended in PBS as the sample.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) CAD layout of the micro flow cytometer chip, (b) junction region designed to eliminate reverse flow, (c) chevron structures on the top and bottom of the channel, (d) expanded view of the detection region

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Figure 2

Process steps for fabrication of the flow cytometer chip

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Figure 3

Photograph of the fabricated chip showing zoomed view of the chevrons

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Figure 4

Conceptual layout of the flow stabilizer chip

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Figure 5

Process flow for fabrication of the stabilizer chip

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Figure 6

Images of the fabricated flow stabilizer chips with PDMS membrane

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Figure 7

(a) Schematic of a cross-flow filter showing concept of filtration and concentration, (b) photograph of a cross-flow filter, (c) SEM image of section of a filter membrane

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Figure 8

Conceptual representation of the scheme of the system fluidics

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Figure 9

Sample core profile (a) before chevrons, (b) after 4-pairs of chevrons, (c) after 7-pairs of chevrons

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Figure 10

Time dependence of flow rate (a) without stabilizer chip and (b) with stabilizer chip

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Figure 11

Influence of (a) chamber volume and (b) Young’s modulus on flow stabilization

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Figure 12

Microscopic image of (a) diluted sample at the inlet of the cross-flow filter, (b) concentrated sample at the outlet of the cross-flow filter

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Figure 13

(a) Comparison of absorbance measured for the feed, concentrated sample and filtrate, (b) variation of cell concentration with filtrate to sample flow rate ratio

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Figure 14

Voltage-time spectrum due to passing of microbeads through the detection point 17

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Figure 15

Scatter plot showing forward scatter (FSC) and side scatter (SSC) of the microbeads

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