Free-Solution, Label-Free Molecular Interactions Studied by Back-Scattering Interferometry
Darryl J. Bornhop,1*
Joey C. Latham,2
Amanda Kussrow,1
Dmitry A. Markov,3
Richard D. Jones,1
Henrik S. Sørensen4
Free-solution, label-free molecular interactions were investigated
with back-scattering interferometry in a simple optical train
composed of a helium-neon laser, a microfluidic channel, and
a position sensor. Molecular binding interactions between proteins,
ions and protein, and small molecules and protein, were determined
with high dynamic range dissociation constants (
Kd spanning
six decades) and unmatched sensitivity (picomolar
Kd's and detection
limits of 10,000s of molecules). With this technique, equilibrium
dissociation constants were quantified for protein A and immunoglobulin
G, interleukin-2 with its monoclonal antibody, and calmodulin
with calcium ion Ca
2+, a small molecule inhibitor, the protein
calcineurin, and the M13 peptide. The high sensitivity of back-scattering
interferometry and small volumes of microfluidics allowed the
entire calmodulin assay to be performed with 200 picomoles of
solute.
2 Department of Biochemistry, Vanderbilt University School of Medicine, 465 21st Avenue South, Suite 9160 MRBIII, Nashville, TN 37232, USA.
3 Department of Biomedical Engineering and Vanderbilt Institute for Integrative Biosystems Research and Education (VIIBRE), Vanderbilt University, 5824 Stevenson Center, Nashville, TN 37235, USA.
4 Optics and Plasma Research Department, Risø National Laboratory, Technical University of Denmark, Building 128, Frederiksborgvej 399–DK-4000-Roskilde, Denmark.
* To whom correspondence should be addressed. E-mail: darryl.bornhop{at}vanderbilt.edu
