title: Attomolar protein detection using a magnetic bead surface coverage assay.
abstract: We demonstrate a microfluidic method for ultra-sensitive protein detection in serum. First, 'large' (2.8 μm) antibody-functionalized magnetic beads specifically capture antigen from a serum matrix under active microfluidic mixing. Subsequently, the large beads loaded with the antigens are gently exposed to a surface pattern of fixed 'small' (1.0 μm) antibody-coated magnetic beads. During the exposure, attractive magnetic bead dipole-dipole interactions improve the contact between the two bead types and help the antigen-antibody immunocomplex formation, while non-specific large bead adsorption is limited by exploiting viscous drag forces in the microfluidic channel on the small-bead pattern. This efficient antigen-antibody recognition and binding mechanism mimics a biological process of selective recognition of tissue molecules, like is the case when leukocytes roll and slow down on blood vessel walls by selectin-mediated adhesion. After exposure of the large beads to the pattern of small beads, the antigen concentration is detected by simply counting the number of surface pattern-bound large magnetic beads. The new technique allows detection of proteins down to the sub-zeptomole range. In particular, we demonstrate detection of only 200 molecules of Tumor Necrosis Factor-α (TNF-α) in a serum sample volume of 5 μL, corresponding to a concentration of 60 attomolar or 1 fg mL(-1).
authors: Laboratory of Microsystems, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland.
authors: H Cumhur
authors: HC
authors: Tekin
authors: Matteo
authors: M
authors: Cornaglia
authors: Martin A M
authors: MA
authors: Gijs
mesh_terms: D000906:Antibodies / Q000276:immunology; D005898:Glass / Q000737:chemistry; D006801:Humans; D018189:Immunomagnetic Separation; D007962:Leukocytes / Q000166:cytology / Q000378:metabolism; D008280:Magnetics; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation / Q000379:methods*; D014409:Tumor Necrosis Factor-alpha / Q000097:blood* / Q000302:isolation & purification
chemical_list: D000906:Antibodies; D014409:Tumor Necrosis Factor-alpha