A microfluidic timer for timed valving and pumping in centrifugal microfluidics.

F Schwemmer,N Paust,F Von Stetten,S Zehnle,R Zengerle,D Mark

doi:10.1039/c4lc01269k

F Schwemmer, N Paust + Show 4 more

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https://doi.org/10.1039/c4lc01269k

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Abstract

Accurate timing of microfluidic operations is essential for the automation of complex laboratory workflows, in particular for the supply of sample and reagents. Here we present a new unit operation for timed valving and pumping in centrifugal microfluidics. It is based on temporary storage of pneumatic energy and time delayed sudden release of said energy. The timer is loaded at a relatively higher spinning frequency. The countdown is started by reducing to a relatively lower release frequency, at which the timer is released after a pre-defined delay time. We demonstrate timing for 1) the sequential release of 4 liquids at times of 2.7 s ± 0.2 s, 14.0 s ± 0.5 s, 43.4 s ± 1.0 s and 133.8 s ± 2.3 s, 2) timed valving of typical assay reagents (contact angles 36-78°, viscosities 0.9-5.6 mPa s) and 3) on demand valving of liquids from 4 inlet chambers in any user defined sequence controlled by the spinning protocol. The microfluidic timer is compatible to all wetting properties and viscosities of common assay reagents and does neither require assistive equipment, nor coatings. It can be monolithically integrated into a microfluidic test carrier and is compatible to scalable fabrication technologies such as thermoforming or injection molding.

Highlights

We demonstrate timing for 1) the sequential release of 4 liquids at times of 2.7 s ± 0.2 s, 14.0 s ± 0.5 s, 43.4 s ± 1.0 s and 133.8 s ± 2.3 s, 2) timed valving of typical assay reagents and 3) on demand valving of liquids from 4 inlet chambers in any user defined sequence controlled by the spinning protocol
Centrifugal microfluidics is a powerful tool for automation of bio-chemical assays[1,2,3,4] with significant advantages when compared to other microfluidic automation concepts: artificial gravity by centrifugation inherently removes bubbles that might interfere with suitable assay performance and the centrifugal propulsion allows for the automation of complex assay protocols without any interfaces to external valves and pumps
We introduced a microfluidic timer that can be used for timed release of liquid reagents with different properties such as viscosities and surface tensions

Summary

Introduction

Centrifugal microfluidics is a powerful tool for automation of bio-chemical assays[1,2,3,4] with significant advantages when compared to other microfluidic automation concepts: artificial gravity by centrifugation inherently removes bubbles that might interfere with suitable assay performance and the centrifugal propulsion allows for the automation of complex assay protocols without any interfaces to external valves and pumps. Timing without employing external means, referred to as passive timing, can be realized by employing capillary forces Such passive timing is commonly used in capillary flow based microfluidics, by designing fluidic resistances in combination with surface tension-based passive pumping or geometric valves.[12,13]. Passive valves are typically triggered at increasingly high rotational frequencies For this purpose, geometric valves,[14] hydrophobic patches[15] and centrifugo-pneumatic valves[16,17,18] are used. The accurate control of such dependencies is challenging and leads to considerable variations in rotational burst frequencies, as for example discussed

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