Trapping of DNA by thermophoretic depletion and convection

Thermophoresis depletes DNA from a heated spot. We quantify for the first time the thermal diffusion constant D-T=0.4x10(-8) cm(2)/s K for DNA, using fluorescent dyes and laser heating. For 5 kB DNA we extrapolate a 1000-fold depletion from a temperature difference of 50 K. Surprisingly, convection generated by the same heating can turn the depletion into trapping of DNA. Trapped DNA can form point geometries 20 mum in diameter with more than 1000-fold enhanced concentrations. The accumulation is driven only by temperature gradients and offers a new approach to biological microfluidics and replicating systems in prebiotic evolution.