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Long-Time Stretched Exponential Kinetics in Single DNA Duplex Dissociation

Paul L. Biancaniello ^*, Anthony J. Kim  and John C. Crocker 

^* Department of Physics and Astronomy and Department of Chemical and Biomolecular Engineering, The University of Pennsylvania, Philadelphia, Pennsylvania

Correspondence: Address reprint requests to John C. Crocker, Tel.: 215-898-9188; E-mail: jcrocker{at}seas.upenn.edu.

We probe DNA hybridization kinetics by measuring the lifetime distribution of single 16-bp duplexes under thermal dissociation. Our unique approach, based on two DNA-coated microspheres in an extended optical tweezer, allows the study of single duplex DNA molecules under negligible molecular tension. In contrast to earlier experiments, we find a stretched exponential lifetime distribution, which is likely due to dissociation proceeding via a number of competing pathways between highly force-sensitive intermediate states. Similar measurements of microspheres linked by multiple DNA bridges find they have unexpected short bound lifetimes, also consistent with force sensitivity.