Dresden 2009 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 15: POSTERS Dynamics and Diffusion
CPP 15.13: Poster
Tuesday, March 24, 2009, 14:00–16:30, P3
Thermal trapping of single molecules in liquids — •Romy Radünz1, Frank Cichos1, and Alois Würger2 — 1Molecular Photonics Group, Institute of Experimental Physics I, University Leipzig, Linnéstr. 5, 04103 Leipzig, Germany — 2CPMOH, Université Bordeaux 1, 351 Cours de la Libération, 33405 Talence, France
Brownian motion prevents an extended optical observation of single molecules in solution as it drives molecular species out of the observation volume. To overcome this drawback surface chemistry is applied to immobilize molecular entities for detailed optical studies. But the presence of a surface may change the electrical, optical and conformational properties of molecules considerably. Thus contact-free methods are needed to confine single molecules or nanoparticles to an observation volume appropriate for optical investigation. Such a trapping in liquids paired with manipulative tools could open a completely new route for single molecule chemistry in solution. Here we propose a thermal trap, which is based on highly localized temperature gradients. Such gradients exert forces on molecules, known as thermophoretic forces. Localized temperature gradients in the fluid are realized by single gold nanoparticles of a diameter of approximately 50 nm, which are immobilized on glass cover slips and selectively excited by a focussed laser beam. Due to the fact that gold nanoparticle exhibit a large absorption cross section near the plasmon resonance they represent very efficient nano heat-sources. In this contribution detailed theoretical considerations on the thermophoretic trap are presented. First experimental results on the trapping of polystyrene beads will be shown.