title: Three-dimensional magnetic focusing of superparamagnetic beads for on-chip agglutination assays.
abstract: We present a new method for three-dimensional (3D) magneticfocusing of magnetic microparticles in a microfluidic system. On-chip magnetic particle manipulation in the microchannel is achieved by a high-gradient magnetic field generated by means of a micromachined field concentrator. The system allows retention of functionalized beads in a dense plug while flowing through buffer or analyte. Slowly reducing the magnetic retention force in the presence of a flow results in controlled release of the particles into a fine streamline with regular longitudinal interparticle spacing. Alignment at half-height of the channel is readily obtained through the symmetry of the magnetic field. A single lateral sheath flow is required to provide full 3D focusing of the microparticles in the middle of the microchannel with a maximum deviation of ±5 μm from the center position. With the use of this system, a new approach for performing an immunoagglutination assay on-chip has been implemented. Three-dimensional focusing allowed reliable counting of singlets and agglutinated doublets. We demonstrate the potential of the agglutination assay in a microfluidic format using a streptavidin/biotinylated bovine serum albumin (bBSA) model system. A detection limit of about 400 pg/mL (6 pM) is achieved.
authors.affiliation: Laboratory of Microsystems, Ecole Polytechnique Fédérale de Lausanne, STI-LMIS2 BM, Lausanne, Switzerland. rana.afshar@epfl.ch
authors.forename: R
authors.initials: R
authors.lastname: Afshar
authors.forename: Y
authors.initials: Y
authors.lastname: Moser
authors.forename: T
authors.initials: T
authors.lastname: Lehnert
authors.forename: M A M
authors.initials: MA
authors.lastname: Gijs
mesh_terms: D000818:Animals; D002417:Cattle; D008280:Magnetics; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation / Q000379:methods*; D012710:Serum Albumin, Bovine / Q000032:analysis
chemical_list: D012710:Serum Albumin, Bovine