Technical Brief

A Very Low-Cost, Labor-Efficient, and Simple Method to Block Scattered Ultraviolet Light in PDMS Microfluidic Devices by Inserting Aluminum Foil Strips

[+] Author and Article Information
Shuo Wang

Department of Mechanical
Engineering-Engineering Mechanics,
Michigan Technological University,
1400 Townsend Drive,
Houghton, MI 49931

Peter Shankles, Scott Retterer

Biosciences & Center for Nanophase
Materials Sciences Divisions,
Oak Ridge National Laboratory,
Oak Ridge, TN 37831;
Bredesen Center for Interdisciplinary
Research and Graduate Education,
The University of Tennessee,
Knoxville, TN 37996

Yong Tae Kang

School of Mechanical Engineering,
Korea University,
145 Anam-ro, Anam-dong, Seongbuk-gu,
Seoul 02841, South Korea

Chang Kyoung Choi

Department of Mechanical
Engineering-Engineering Mechanics,
Michigan Technological University,
1400 Townsend Drive,
Houghton, MI 49931
e-mail: cchoi@mtu.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received June 3, 2018; final manuscript received August 12, 2018; published online October 15, 2018. Assoc. Editor: Cheng-Xian Lin.

J. Thermal Sci. Eng. Appl 11(1), 014501 (Oct 15, 2018) (3 pages) Paper No: TSEA-18-1288; doi: 10.1115/1.4041436 History: Received June 03, 2018; Revised August 12, 2018

Opto-microfluidic methods have advantages for manufacturing complex shapes or structures of micro particles/hydrogels. Most of these microfluidic devices are made of polydimethylsiloxane (PDMS) by soft lithography because of its flexibility of designing and manufacturing. However, PDMS scatters ultraviolet (UV) light, which polymerizes the photocrosslinkable materials at undesirable locations and clogs the microfluidic devices. A fluorescent dye has previously been employed to absorb the scattered UV light and shift its wavelength to effectively solve this issue. However, this method is limited due to the cost of the materials (tens of dollars per microchip), the time consumed on synthesizing the fluorescent material and verifying its quality (two to three days). More importantly, significant expertise on material synthesis and characterization is required for users of the opto-microfluidic technique. The cost of preliminary testing on multiple iterations of different microfluidic chip designs would also be excessive. Alternatively, with a delicate microchannel design, we simply inserted aluminum foil strips (AFS) inside the PDMS device to block the scattered UV light. By using this method, the UV light was limited to the exposure region so that the opto-microfluidic device could consistently generate microgels longer than 6 h. This is a nearly cost- and labor-free method to solve this issue.

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Grahic Jump Location
Fig. 1

UV light blocking method using AFS. (a) The actual image and schematics of the present method. (b) The intensity of scattered UV was measured by a UV light radiometer at the flow-focusing section from two directions. (c) The noticeable difference of light intensity between the two sides of the foil strips and the microchannel that was illuminated by the reflected/refracted UV light. (d) The old version of AFS method: two pieces of AFS were vertically inserted from top and bottom, and one piece was horizontally inserted from two sides. Because of the presence of the microchannel, the vertical AFS only could not fully cover the cross section of the microchip, leaving a UV-leaking area, which is denoted in the figure by the arrowheads. Scale bar: 100 μm.

Grahic Jump Location
Fig. 2

Quantified effectiveness of the AFS method on blocking scattered UV light. The radiometer was placed at the side (location 1) and at the bottom (location 2) of the microchip to measure the intensity of scattered UV light at the flow-focusing section. The standard deviations are the error bars.



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