Free-solution, label-free molecular interactions studied by back-scattering interferometry

Science. 2007 Sep 21;317(5845):1732-6. doi: 10.1126/science.1146559.


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 Ca2+, 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.

Publication types

  • Evaluation Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Calcineurin / chemistry
  • Calcium / chemistry
  • Calmodulin / chemistry
  • Dimethylpolysiloxanes
  • Humans
  • Immunoglobulin G / chemistry
  • Interferometry / methods*
  • Kinetics
  • Molecular Sequence Data
  • Myosin-Light-Chain Kinase / chemistry
  • Peptide Fragments / chemistry
  • Protein Binding*
  • Rabbits
  • Refractometry
  • Silicones
  • Solutions


  • Calmodulin
  • Dimethylpolysiloxanes
  • Immunoglobulin G
  • M13 protein (myosin light-chain kinase)
  • Peptide Fragments
  • Silicones
  • Solutions
  • baysilon
  • Myosin-Light-Chain Kinase
  • Calcineurin
  • Calcium