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Formation of droplets of alternating composition in microfluidic channels and applications to indexing of concentrations in droplet-based assays

Zheng, Bo and Tice, Joshua D. and Ismagilov, Rustem F. (2004) Formation of droplets of alternating composition in microfluidic channels and applications to indexing of concentrations in droplet-based assays. Analytical Chemistry, 76 (17). pp. 4977-4982. ISSN 0003-2700. doi:10.1021/ac0495743.

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For screening the conditions for a reaction by using droplets (or plugs) as microreactors, the composition of the droplets must be indexed. Indexing here refers to measuring the concentration of a solute by addition of a marker, either internal or external. Indexing may be performed by forming droplet pairs, where in each pair the first droplet is used to conduct the reaction, and the second droplet is used to index the composition of the first droplet. This paper characterizes a method for creating droplet pairs by generating alternating droplets, of two sets of aqueous solutions in a flow of immiscible carrier fluid within PDMS and glass microfluidic channels. The paper also demonstrates that the technique can be used to index the composition of the droplets, and this application is illustrated by screening conditions of protein crystallization. The fluid properties required to form the steady flow of the alternating droplets in a microchannel were characterized as a function of the capillary number Ca and water fraction. Four regimes were observed. At the lowest values of Ca, the droplets of the two streams coalesced; at intermediate values of Ca the alternating droplets formed reliably. At even higher values of Ca, shear forces dominated and caused formation of droplets that were smaller than the cross-sectional dimension of the channel; at the highest values of Ca, coflowing laminar streams of the two immiscible fluids formed. In addition to screening of protein crystallization conditions, understanding of the fluid flow in this system may extend this indexing approach to other chemical and biological assays performed on a microfluidic chip.

Item Type:Article
Related URLs:
URLURL TypeDescription CentralArticle
Zheng, Bo0000-0001-8344-3445
Ismagilov, Rustem F.0000-0002-3680-4399
Additional Information:Copyright © 2004 American Chemical Society. Published In Issue: September 01, 2004. Received for review March 18, 2004. Accepted June 9, 2004. This work was supported by the NIH (R01 EB001903) and was performed at the MRSEC microfluidic facility funded by NSF. J.D.T. is a Beckman Fellow. We thank Wendy Zhang for helpful discussions.
Funding AgencyGrant Number
NIBIBR01 EB001903
Arnold and Mabel Beckman FoundationUNSPECIFIED
Subject Keywords:protein crystallization conditions; linear flow; coalescence; systems; poly(dimethylsiloxane); compatibilizer; microchannels; deformation; generation; kinetics
Issue or Number:17
Record Number:CaltechAUTHORS:20130821-160736217
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:40895
Deposited By: Whitney Barlow
Deposited On:28 Aug 2013 20:29
Last Modified:10 Nov 2021 04:23

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