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Hydrodynamic Focusing and Rapid Mixing


PIs: J. Grogan and H. H. Bau

To measure reaction kinetics and protein folding, the mass transfer of the reagents (mixing) must be faster than the reaction kinetics. This is accomplished by focusing the analyte stream into a thin jet. Similar ideas can be used for flow cytometry.

Hydrodynamic Focusing

  • Two Perpendicular streams meet at a cross junction and travel parallel to each other.
  • One control the width of the “jet” by controlling the flow rates of the jet and sheath flows. The width of the center stream can be “focused” down to be very thin.
  • The jet and sheath streams mix laterally as they flow.
  • The reactions can be observed with no dead time

Fabrication by Soft Lithography

  • Microfabricated molds are produced by photolithography using SU-8 negative photoresist.
  • Liquid PDMS (polydimethylsiloxane) is cast on the molds and cured.
  • PDMS is removed from the mold and bonded to glass or another PDMS layer.
  • PDMS is transparent to UV and visible light facilitating fluorescence microscopy.


Devices have been successfully fabricated and are being applied to kinetic investigations.



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