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AKB: Biologische Physik

AKB 15: Biopolymers II

AKB 15.7: Vortrag

Dienstag, 28. März 2006, 18:00–18:15, ZEU 260

Thermophoresis is Entropophoresis — •Stefan Duhr and Dieter Braun — Noether Group on Dissipative Microsystems, Applied Physics, Ludwig Maximilians Universität München, Amalienstr. 54, 80799 München, Germany

Molecules move along temperature gradients, a phenomenon known from experiments for 150. The effect is called thermophoresis, Soret-effect or thermal diffusion. Here we present experiments which back a unifying theoretical explanation. Measurements span a wide range of molecule types and sizes, possible by the use of a novel fluorescence technique which measures thermophoresis in 10 picoliter microfluidics. Optically imposed temperature patterns are shown to manipulate molecules in solution on the micron scale. Our experiments demonstrate that thermophoresis is driven by the entropy of solvation. In water, two solvation entropies counteract. Entropy of ionic shielding leads to thermophobic depletion. Entropy of hydration results in thermophilic accumulation at low overall temperatures. The theory predicts thermophoresis of polystyrene beads and DNA with 10 % accuracy without free parameters. It allows the determination of the effective charge and hydration entropy over a wide molecule size range not measurable with electrophoresis. With this theoretical foundation, thermophoresis can be used for all-optical quantitative biomolecule analysis.