In this Letter, we report direct measurement of large low frequency temperature fluctuations in double stranded DNA when it undergoes a denaturation transition. The fluctuation, which occurs only in the temperature range where the denaturation occurs, is several orders more than the expected equilibrium fluctuation. It is absent in single stranded DNA of the same sequence. The fluctuation at a given temperature also depends on the wait time and vanishes in a scale of a few hours. It is suggested that the large fluctuation occurs due to coexisting denaturated and closed base pairs that are in dynamic equilibrium due to the transition through a potential barrier in the scale of $25–30k_B{T}_0$ ($T_0=300\mathrm{K}$).

• Received 24 December 2004

DOI:https://doi.org/10.1103/PhysRevLett.96.038102