Trapping of DNA by Thermophoretic Depletion and Convection

Abstract

Thermophoresis depletes DNA from a heated spot. We quantify for the first time the thermal diffusion constant ${D}_{T}=0.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\text{ }{\mathrm{c}\mathrm{m}}^{2}/\mathrm{s}\text{ }\mathrm{K}$ 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 $20\text{ }\ensuremath{\mu}\mathrm{m}$ 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.