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. Nov-Dec 2004;80(3):482-5.
doi: 10.1562/0031-8655(2004)080<0482:SPPEON>2.0.CO;2.

Surface Plasmon-Coupled Polarized Emission of N-acetyl-l-tryptophanamide

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Surface Plasmon-Coupled Polarized Emission of N-acetyl-l-tryptophanamide

Ignacy Gryczynski et al. Photochem Photobiol. .
Free PMC article

Abstract

We report an observation of ultraviolet (UV) surface plasmon-coupled emission (SPCE) of N-acetyl-l-tryptophanamide (NATA). The sample was spin coated from poly(vinyl alcohol) (PVA) solution on 20 nm aluminum film deposited on a quartz substrate. The directional UV SPCE occurs within a well-defined narrow angle at 52 degrees from the normal to the coupling hemicylinder quartz prism. The NATA directional emission is highly p polarized as expected for surface plasmon-coupled radiation. The 10 nm protective SiO2 layer deposited on top of the aluminum film significantly neutralized the fluorophore quenching by the metal surface. SPCE of NATA demonstrates a remarkable intrinsic dispersive property-the maximum of the emission spectrum depends on the observation angle. The efficient spectral resolution of SPCE can be used in the construction of miniaturized spectrofluorometers. The observation of SPCE of tryptophan opens a new possibility for the study of many unlabeled proteins with the technique complementary to surface plasmon resonance analysis.

Figures

Figure 1.
Figure 1.
Emission spectra of NATA spin coated from PVA solution on unmetallized quartz (top) and on aluminum-coated quartz slide (bottom). The fluorescence intensities do not differ for bare quartz and the silica-protected aluminum surface. The dotted lines represent backgrounds from the reference slide without NATA.
Figure 2.
Figure 2.
Top, left: The polarized SPCE of NATA observed at 52°. The 297 nm excitation was vertically (V) polarized. The observation polarizer was either vertically (s) or horizontally (H) oriented (p). The dotted line is the background from the reference slide without NATA, observed through a horizontally oriented polarizer. Top, right: angular distribution of NATA SPCE measured in RK/SPCE configuration. Bottom: the reflectance angular profile calculated for a five-phase system with an assumed PVA thickness of 12 nm.
Figure 3.
Figure 3.
Observation angle–dependent spectra of NATA SPCE measured in RK/SPCE configuration. About 40 nm/10° resolution is provided by intrinsic dispersive properties of SPCE.
Figure 4.
Figure 4.
Frequency domain lifetimes of NATA spin coated from 0.5% PVA solution in various configurations. Top, on bare quartz; middle, on protected aluminum; bottom, on protected aluminum with RK/SPCE configuration. Only modest changes in lifetimes were observed.
Scheme 1.
Scheme 1.
Sample configuration for SPCE of tryptophan. The metallized quartz slide spin coated with PVA-containing NATA was attached to a hemicylindrical quartz prism (the layer thickness is drawn not to the scale). The excited NATA dipoles couple to the surface plasmons, which radiate within the narrow hollow cone at the angle θF. The SPCE radiation is fully p polarized.

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