Berlin 2005 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 36: Single molecules II

CPP 36.1: Talk

Wednesday, March 9, 2005, 11:15–11:30, TU C243

Enhanced chromophore performance and single-molecule detection near a metal surface — •Maximilian Kreiter, Fernando Stefani, Krasimir Vasilev, and Volker Jacobsen — Max Planck Institut für Polymerforschung, Ackermannweg 10 D-55128 Mainz

A nearby metal film is known [1] to influence the excitation and emission rates of nearby chromophores, for both effects surface plasmons play a major role. We present a detailed quantitative study of these effects which became possible due to an improved sample preparation with ultraflat layers. Intensity as a function of excitation and emission direction is studied and found to be in quantitative agreement with the classical predictions down to a chromophore-metal separation of 10 nm where a significant deviation is found [2]. The photostability of the dyes turns out to be enhanced by the nearby metal [3]. In a scanning confocal optical microscope, detection of single fluorescent molecules is possible thorugh the metal. The observed patterns are modeled quantitatively and it is found that the main excitation and emission channels are via intermediate excitation of surface plasmons, leading to a preferential detection of dipoles perpendicular to the surface. This is experimentally proven by choosing different illumination modes. It turns out that the total number of photons that can be obtained from one chromophore is enhanced by a factor of 1.4 by the presence of the metal film.

[1] K. H. Drexhage et al. Ber. Bunsenges. Phys. Chem. 70, 1179 (1966)

[2] K. Vasilev et al. J. Chem. Phys. 120, 3439 (2004)

[3] K. Vasilev et al. J. Chem. Phys. 120, 6701 (2004)