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Proceedings Paper

High-sensitivity measurement of free-protein concentration using optical tweezers
Author(s): Osman Akcakir; Chris R. Knutson; Crystal Duke; Evan Tanner; Daniel M. Mueth; Joseph S. Plewa; Kenneth F. Bradley
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Paper Abstract

We have applied optical tweezers to measure the free-protein concentration of a microscopic sample in the nM range by measuring the optical tweezer laser power at which protein coated beads are ruptured from an antibody coated coverslip surface. We used silica beads that were covalently coated with a target protein and a glass coverslip coated with antibodies specific against the target protein, causing the coated beads to stick to the surface. The unknown unlabelled target protein concentration was added, which then competed with the bead-bound target protein for antibody binding sites on the coverslip surface. In this way the number of bead-surface bonds were modulated by the free protein concentration in solution affecting the threshold laser power necessary to rupture the bead from the surface. An optical tweezer was used to probe the number of bead-surface bonds by measuring the threshold power required to pull the bead away from the surface. We positioned an optical tweezer (1064 nm) slightly above the bead and linearly ramped the laser power until the bead ruptured from the surface. The power at which this occurred was used to determine the free protein concentration. Our measured calibration curve of threshold power versus free protein concentration was fitted to a single binding site equilibrium model which yielded an estimate for the equilibrium dissociation coefficient that is comparable to literature values.

Paper Details

Date Published: 22 February 2008
PDF: 11 pages
Proc. SPIE 6863, Optical Diagnostics and Sensing VIII, 686305 (22 February 2008); doi: 10.1117/12.763924
Show Author Affiliations
Osman Akcakir, Arryx, Inc. (United States)
Chris R. Knutson, Arryx, Inc. (United States)
Crystal Duke, Arryx, Inc. (United States)
Evan Tanner, Arryx, Inc. (United States)
Daniel M. Mueth, Arryx, Inc. (United States)
Joseph S. Plewa, Arryx, Inc. (United States)
Kenneth F. Bradley, Arryx, Inc. (United States)

Published in SPIE Proceedings Vol. 6863:
Optical Diagnostics and Sensing VIII
Gerard L. Coté; Alexander V. Priezzhev, Editor(s)

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