Clinical Chemistry
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Clinical Chemistry 52: 2135-2140, 2006. First published September 21, 2006; 10.1373/clinchem.2006.072793
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(Clinical Chemistry. 2006;52:2135-2140.)
© 2006 American Association for Clinical Chemistry, Inc.

Oak Ridge Conference

High-Speed Interferometric Detection of Label-Free Immunoassays on the Biological Compact Disc

Ming Zhao1, David Nolte1,a, Wonryeon Cho2, Fred Regnier2, Manoj Varma3, Greg Lawrence3 and John Pasqua3

Departments of1 Physics and2 Chemistry, Purdue University, West Lafayette, IN.
3 QuadraSpec Inc., West Lafayette, IN.

aAddress correspondence to this author at: Department of Physics, Purdue University, West Lafayette, IN 47907. Fax: 765-494-0706; e-mail nolte{at}physics.purdue.edu.


Abstract

Background: We describe a direct-detection immunoassay that uses high-speed optical interferometry on a biological compact disc (BioCD).

Methods: We fabricated phase-contrast BioCDs from 100-mm diameter 1.1-mm thick borosilicate glass disks coated with a 10-layer dielectric stack of Ta2O5/SiO2 that serves as a mirror with a center wavelength at 635 nm. The final layer is a {lambda}/4 layer of SiO2 onto which protein patterns are immobilized through several different chemical approaches. Protein on the disc is scanned by a focused laser spot as the disc spins. Interaction of the light with the protein provides both a phase-modulated signal and a local reference that are combined interferometrically to convert phase into intensity. A periodic pattern of protein on the spinning disc produces an intensity modulation as a function of time that is proportional to the surface-bound mass. The binding of antigen or antibodies is detected directly, without labels, by a change in the interferometric intensity. The technique is demonstrated with a reverse assay of immobilized rabbit and mouse IgG antigen incubated against anti-IgG antibody in a casein buffer.

Results: The signal increased with increased concentration of analyte. The current embodiment detected a concentration of 100 ng/L when averaged over ~3000 100-micron-diameter protein spots.

Conclusions: High-speed interferometric detection of label-free protein assays on a rapidly spinning BioCD is a high-sensitivity approach that is amenable to scaling up to many analytes.




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D. J. Bornhop, J. C. Latham, A. Kussrow, D. A. Markov, R. D. Jones, and H. S. Sorensen
Free-Solution, Label-Free Molecular Interactions Studied by Back-Scattering Interferometry
Science, September 21, 2007; 317(5845): 1732 - 1736.
[Abstract] [Full Text] [PDF]


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