A STUDY OF SURFACE PLASMON-COUPLED EMISSION FROM RHODAMINE 6G USING PICOSECOND PULSES AND CONTINUOUS WAVE LIGHT

Abstract

Fluorescence measurements are used in life sciences to provide important information about biomolecules (fluorophores) such as structure and conformational changes by detecting the target molecules on surfaces. Currently, fluorescence measurements are performed using free-space (FS) detection, which are mostly isotropic, resulting in detection of approximately 1% of the total emission. The emission process may be limited by the background fluorescence due to its isotropic nature and, photochemical destruction of the fluorophores. Surface Plasmon-Coupled Emission (SPCE) is a fluorescence technique that has been recently introduced that increases the fluorescence yield. SPCE is based on the interaction of excited-state fluorophores with a nearby metal surface. The fluorophores above the metal surface can couple with the plasmon resonances in the metal, resulting in directional and wavelength-resolved emission. The coupled emission is characterized by a dependence of the emission wavelength on the emission angle. In addition, the emission is horizontally (p) polarized. An advantage of the SPCE over FS signal is the reduction of the background fluorescence signal, since only fluorophores close to the metal surface will couple to the surface plasmons. Picosecond pulses were used to study the SPCE properties of Rhodamine 6G fluorophore on a thin silver film. It is expected that using pulsed laser sources can greatly enhance the SPCE signal over the FS signal. The SPCE signal is 3 times higher that the isotropic FS signal. Thus, SPCE technique under pulsed excitation promises to be an effective tool for fluorescence measurements in investigating the optical properties of biomolecules.