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Anal Chem. 2013 Dec 17;85(24):11695-9. doi: 10.1021/ac402169x. Epub 2013 Nov 25.

Tunable membranes for free-flow zone electrophoresis in PDMS microchip using guided self-assembly of silica microbeads.

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  • 1Department of Electrical Engineering and Computer Science, ‡Department of Biological Engineering, §Department of Chemistry, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, MA 02139, United States.


In this paper, we evaluate the strategy of using self-assembled microbeads to build a robust and tunable membrane for free-flow zone electrophoresis in a PDMS microfluidic chip. To fabricate a porous membrane as a salt bridge for free-flow zone electrophoresis, we used silica or polystyrene microbeads between 3-6 μm in diameter and packed them inside a microchannel. After complete evaporation, we infiltrated the porous microbead structure with a positively or negatively charged hydrogel to modify its surface charge polarity. Using this device, we demonstrated binary sorting (separation of positive and negative species at a given pH) of peptides and dyes in standard buffer systems without using sheath flows. The sample loss during sorting could be minimized by using ion selectivity of hydrogel-infiltrated microbead membranes. Our fabrication method enables building a robust membrane for pressure-driven free-flow zone electrophoresis with tunable pore size as well as surface charge polarity.

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