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AKB: Biologische Physik

AKB 28: Single Molecule Probes

AKB 28.4: Talk

Friday, March 31, 2006, 12:45–13:00, ZEU 255

Metal coated full body glass tips as high resolution probes for SNOM fluorescence imaging — •Heinrich Gotthard Frey¹, Carsten Bolwien², Robert Ros¹, and Dario Anselmetti¹ — ¹Experimentelle Biophysik und angewandte Nanowissenschaften, Fakultät für Physik, Universität Bielefeld, Universitätsstraße 25, 33615 Bielefeld — ²Frauenhofer-Institut für Physikalische Messtechnik IPM, Heidenhofstraße 8, 79110 Freiburg

For biological applications, scanning near-field optical microscopy of single fluorescent dye molecules require probes which combine high near-field intensities with high optical and topographical resolution.

Such probes can be realised by full body glass tips completely covered by a thin metal layer. In order to achieve strong fields at the tip apex, it is important to illuminate the tip under an inclination angle with the polarisation parallel to the inclination plane. Optimised values for metal layer thickness and inclination angle have been investigated by multiple multipole simulation showing that the achievable optical resolution is roughly given by the tip radius.

These probes have been tested by imaging single fluorescent dye molecules. They show fluorescence patterns with one or two peaks, which can be explained by means of the electrical field distribution at the tip apex. For an aluminium coated tip with 25 nm tip radius, the fluorescence patterns have peaks with a full width half maximum of about 15 nm.

This optical probe is especially suited for cantilever probes, where the inclined illumination can easily be realised.