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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.