title: Whole blood immunoassay based on centrifugal bead sedimentation.
abstract: BACKGROUND
  Centrifugal "lab on a disk" microfluidics is a promising avenue for developing portable, low-cost, automated immunoassays. However, the necessity of incorporating multiple wash steps results in complicated designs that increase the time and sample/reagent volumes needed to run assays and raises the probability of errors. We present proof of principle for a disk-based microfluidic immunoassay technique that processes blood samples without conventional wash steps.
  
  
  METHODS
  Microfluidic disks were fabricated from layers of patterned, double-sided tape and polymer sheets. Sample was mixed on-disk with assay capture beads and labeling antibodies. Following incubation, the assay beads were physically separated from the blood cells, plasma, and unbound label by centrifugation through a density medium. A signal-laden pellet formed at the periphery of the disk was analyzed to quantify concentration of the target analyte.
  
  
  RESULTS
  To demonstrate this technique, the inflammation biomarkers C-reactive protein and interleukin-6 were measured from spiked mouse plasma and human whole blood samples. On-disk processing (mixing, labeling, and separation) facilitated direct assays on 1-μL samples with a 15-min sample-to-answer time, <100 pmol/L limit of detection, and 10% CV. We also used a unique single-channel multiplexing technique based on the sedimentation rate of different size or density bead populations.
  
  
  CONCLUSIONS
  This portable microfluidic system is a promising method for rapid, inexpensive, and automated detection of multiple analytes directly from a drop of blood in a point-of-care setting.
authors.affiliation: Biotechnology and Bioengineering Department, Sandia National Laboratories, Livermore, CA 94550, USA.
authors.forename: Ulrich Y
authors.initials: UY
authors.lastname: Schaff
authors.forename: Greg J
authors.initials: GJ
authors.lastname: Sommer
mesh_terms: D000818:Animals; D002097:C-Reactive Protein / Q000032:analysis; D002501:Centrifugation, Zonal; D006801:Humans; D007118:Immunoassay / Q000295:instrumentation / Q000379:methods*; D015850:Interleukin-6 / Q000097:blood; D051379:Mice; D046210:Microfluidic Analytical Techniques; D008863:Microspheres; D010316:Particle Size
chemical_list: D015850:Interleukin-6; D002097:C-Reactive Protein