Berlin 2012 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 11: New Instruments and Methods

CPP 11.7: Vortrag

Dienstag, 27. März 2012, 11:30–11:45, C 243

Twin-Focus Photothermal Correlation Spectroscopy — •Markus Selmke, Marco Braun, Romy Schachoff, and Frank Cichos — Universität Leipzig, Exp. Physik I, molecular nanophotonics

The use of metal nano-particles for probing dynamics and reactions in biology and soft-matter physics has been on the rise due to their superior stability as compared to molecular fluorophores. The successful method of fluorescence correlation spectroscopy (FCS), which quantifies in its simplest form locally the diffusion and mobilities, has found its counterpart for these non-fluorescent but absorbing nano-tracers in PhoCS, photothermal correlation spectroscopy. The signal used in this method for the detection is related to the plasmonic heating of the particles: The power absorbed from a resonant laser (532nm) generates a temperature profile around the particle which in turn causes a refractive index profile which is probed by a second off-resonance laser, typically by means of a lock-in technique. While the lensing action provides a twin-focus split detection-volume in which two non-overlapping regions may be addressed and analyzed individually or in combination it is also clear that the absorption infers momentum to the diffusing particles which may be addressed and studied by the advection-diffusion equation and its effect on various (cross-)correlation functions. These features allow for the sensitive determination of minute flow velocities, either self-induced by radiation pressure or via external forces, and the study of heterogeneous dynamics on the length scale of the split-focus separation (about 500nm).