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  • Title: Phase-changing sacrificial materials for interfacing microfluidics with ion-permeable membranes to create on-chip preconcentrators and electric field gradient focusing microchips.
    Author: Kelly RT, Li Y, Woolley AT.
    Journal: Anal Chem; 2006 Apr 15; 78(8):2565-70. PubMed ID: 16615765.
    Abstract:
    We have developed a novel approach for interfacing ionically conductive membranes with microfluidic systems using phase-changing sacrificial layers. Imprinted microchannels in a polymer substrate are filled with a heated liquid that solidifies at room temperature, a monomer solution is placed over the protected channels and polymerized to form a rigid semipermeable copolymer, and then the protective layer is melted and removed, leaving an open microchannel interfaced with a polymer membrane. We have applied this method in miniaturizing electric field gradient focusing (EFGF) and carrying out on-chip protein preconcentration. A semipermeable copolymer in the EFGF microchips fills a region of changing cross-sectional area, which allows a gradient in electric field to be established when an electrical potential is applied. Our technique provides microchip EFGF devices that offer 3-fold improved resolution in protein focusing compared with capillary-based systems. In addition, these EFGF microchips can separate peptide samples with resolution similar to what is obtained in capillary electrophoresis microdevices, and the micro-EFGF systems enrich analytes by a factor of >150. Finally, we have fabricated membrane-integrated microfluidic devices that can concentrate protein samples (R-phycoerythrin) over 10 000-fold to facilitate microchip capillary electrophoresis. Interfacing microchannels with ion-permeable membranes has great potential to enhance microchip analysis of biomolecules.
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