Long-time stretched exponential kinetics in single DNA duplex dissociation

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.