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Microfluidics and Nanofluidics
Open AccessArticle

Wax-Printed Fluidic Time Delays for Automating Multi-Step Assays in Paper-Based Microfluidic Devices (MicroPADs)

1
Department of Biological Sciences, California Polytechnic State University, San Luis Obispo, CA 93407, USA
2
Department of Chemistry and Biochemistry, California Polytechnic State University, San Luis Obispo, CA 93407, USA
*
Author to whom correspondence should be addressed.
Inventions 2019, 4(1), 20; https://doi.org/10.3390/inventions4010020
Received: 20 February 2019 / Revised: 10 March 2019 / Accepted: 13 March 2019 / Published: 19 March 2019
(This article belongs to the Special Issue Microfluidics and Nanofluidics)
Microfluidic paper-based analytical devices (microPADs) have emerged as a promising platform for point-of-care diagnostic devices. While the inherent wicking properties of microPADs allow for fluid flow without supporting equipment, this also presents a major challenge in achieving robust fluid control, which becomes especially important when performing complex multi-step assays. Herein, we describe an ideal method of fluid control mediated by wax-printed fluidic time delays. This method relies on a simple fabrication technique, does not utilize chemicals/reagents that could affect downstream assays, is readily scalable, and has a wide temporal range of tunable fluid control. The delays are wax printed on both the top and bottom of pre-fabricated microPAD channels, without subsequent heating, to create hemi-/fully-enclosed channels. With these wax printed delays, we were able to tune the time it took aqueous solutions to wick across a 25 mm-long channel between 3.6 min and 13.4 min. We then employed these fluid delays in the sequential delivery of four dyes to a test zone. Additionally, we demonstrated the automation of two simple enzymatic assays with this fluid control modality. This method of fluid control may allow future researchers to automate more complex assays, thereby further advancing microPADs toward real-world applications. View Full-Text
Keywords: microfluidic paper-based analytical devices; microPADs; µPADs; wax printing; multi-step assays; fluid control microfluidic paper-based analytical devices; microPADs; µPADs; wax printing; multi-step assays; fluid control
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MDPI and ACS Style

Strong, E.B.; Knutsen, C.; Wells, J.T.; Jangid, A.R.; Mitchell, M.L.; Martinez, N.W.; Martinez, A.W. Wax-Printed Fluidic Time Delays for Automating Multi-Step Assays in Paper-Based Microfluidic Devices (MicroPADs). Inventions 2019, 4, 20.

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