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 $D_T=0.4\times {10}^{-8}{\mathrm{c}\mathrm{m}}^2/\mathrm{s}\mathrm{K}$ 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 $20\mu \mathrm{m}$ 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.