Saturday, June 8, 2013

Kinetics and non-exponential binding of DNA-coated colloids

William Benjamin Rogers, Talid Sinno and John C. Crocker
Transient bridges of DNA have been used to direct the self-assembly of colloidal particles into interesting soft materials, but the particle binding kinetics are often slow or anomalous. Using line optical tweezers, we quantify the dynamics of two DNA-coated microspheres as a function of DNA density and strength of the DNA-induced pair interaction potential. At high DNA density, the binding kinetics is limited by the rate of microsphere diffusion and displays the expected dependence on the interaction potential energy. At low DNA density, the particle binding kinetics is set by single molecular binding events and exhibits bound times having a non-exponential distribution, suggesting that individual DNA bridges may also have intrinsic non-exponential kinetics. A dynamic model that includes such dispersion in the lifetimes of molecular bridges reproduces our observations, while an alternative model based on fluctuations in DNA density does not.
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