title: Three-dimensional hydrodynamic focusing in a microfluidic Coulter counter.
abstract: Electrical impedance-based particle detection or Coulter counting, offers a lab-on-chip compatible method for flow cytometry. Developments in this area will produce devices with greater portability, lower cost, and lower power requirements than fluorescence-based flow cytometry. Because conventional Coulter apertures are prone to clogging, hydrodynamic focusing improves the device by creating fluid-walled channels with variable width to increase sensitivity without the associated risk of blocking the channel. We describe a device that focuses the sample in three dimensions, creating a narrow sample stream on the floor of the channel for close interaction with sensing electrodes. The key to this design is a stepped outlet channel fabricated in a single layer with soft lithography. In contrast to previous impedance-based designs, the new design requires minimal alignment with the substrate. Three-dimensional focusing maximizes the sensitivity of the device to cell-size particles within much larger channels. Impedance-based particle sensing experiments within this device show an increase in percentage conductivity change by a factor of 2.5 over devices that only focus the sample in the horizontal direction.
authors.affiliation: Electrical and Computer Engineering Department, University of Louisville, Louisville, Kentucky 40208, USA.
authors.forename: R
authors.initials: R
authors.lastname: Scott
authors.forename: P
authors.initials: P
authors.lastname: Sethu
authors.forename: C K
authors.initials: CK
authors.lastname: Harnett
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D005434:Flow Cytometry / Q000295:instrumentation* / Q000379:methods; D017022:Flow Injection Analysis / Q000295:instrumentation* / Q000379:methods; D044085:Microfluidics / Q000295:instrumentation* / Q000379:methods; D014159:Transducers