Issue 14, 2013

On-demand droplet loading for automated organic chemistry on digital microfluidics

Abstract

Organic chemistry applications on digital microfluidic devices often involve reagents that are volatile or sensitive and must be introduced to the chip immediately before use. We present a new technique for automated, on-demand loading of ∼1 μL droplets from large (∼1 mL), sealed, off-chip reservoirs to a digital microfluidic chip in order to address this challenge. Unlike aqueous liquids which generally are non-wetting to the hydrophobic surface and must be actively drawn into the electrowetting-on-dielectric (EWOD) chip by electrode activation, organic liquids tend to be wetting and can spontaneously flood the chip, and hence require a retracting force for controlled liquid delivery. Using a combination of compressed inert gas and gravity to exert driving and retracting forces on the liquid, the simple loading technique enables precise loading of droplets of both wetting and non-wetting liquids in a reliable manner. A key feature from a practical point of view is that all of the wetted parts are inexpensive and potentially disposable, thus avoiding cross-contamination in chemical and biochemical applications. We provide a theoretical treatment of the underlying physics, discuss the effect of geometry and liquid properties on its performance, and show repeatable reagent loading using the technique. Its versatility is demonstrated with the loading of several aqueous and non-aqueous liquids on an EWOD digital microfluidic device.

Graphical abstract: On-demand droplet loading for automated organic chemistry on digital microfluidics

Article information

Article type
Paper
Submitted
11 Dec 2012
Accepted
03 Apr 2013
First published
13 May 2013

Lab Chip, 2013,13, 2785-2795

On-demand droplet loading for automated organic chemistry on digital microfluidics

G. J. Shah, H. Ding, S. Sadeghi, S. Chen, C. “. Kim and R. M. van Dam, Lab Chip, 2013, 13, 2785 DOI: 10.1039/C3LC41363B

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