Berlin 2012 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 2: Nanoparticles and Composite Materials

CPP 2.8: Topical Talk

Montag, 26. März 2012, 11:30–12:00, C 243

Gold nanoparticle assisted thermophoretic trapping of single nano-objects — Marco Braun, Romy Schachoff, and •Frank Cichos — Molecular Nanophotonics Group, University of Leipzig, Linnéstraße 5, D - 04103 Leipzig

Optical tweezing is the most common technique for the trapping of individual particles in solution. It is based on the gradient force of focused electromagnetic radiation. Hence, a sufficient high polarizability contrast between the particle and the solution is required. While it is thus easy to trap single dielectric particles larger than 100 µ m, a trapping of smaller objects such as single molecules by means of an optical tweezer is hardly possible. Molecular trapping can be achieved by a technique called Anti-Brownian Elektrokinetic trap (ABEL trap), which exploits the time-dependent electric field of four electrodes. Here, we present a new technique which replaces the electric field by local thermal fields generated by single Au nanoparticles. The so-called Thermophoretic trap exploits thermophoretic forces that act on a particle placed in a temperature gradient, which e.g. locally distorts the screening of the surface charges. Such forces are sufficient for the manipulation of small nanoparticles or proteins. In our approach, the thermal gradient around optically heated Au nanoparticles immobilized in an appropriate arrangement shall be use to trap single nanoobjects. The plasmonic heating of the separate Au nanoparticles hereby is achieved by a focused laser beam that is controlled by a suitable feedback loop. Numerical simulations as well as first experimental results will be presented.