Extension of a DNA molecule by local heating with a laser.

Thermal convection and thermophoresis induced by mum-scale local heating are shown to elongate a single DNA molecule. An infrared laser used as a point heat source is converged into a dispersion solution of DNA molecules, which is observed under a fluorescent microscope. The thermal convection around the laser focus manifests as extensional flow for the long DNA chain. A simulation of thermal convection that reproduces the experimental condition provides numerical support for the stretching caused by thermal convection. This DNA elongation technique is a novel method for manipulating the intact single DNA molecules, and it can be applied to a "lab on a chip".