Biomedical Engineering Reference
In-Depth Information
entailing luorescence quenching and enhancement using novel
metal nanomaterials for the sensitive analysis of proteins, DNA, and
small solutes.
10.1 Introduction
Noble metal nanoparticles (NPs) containing dye molecules have
recently gained considerable interest in photonics, optoelectronics,
and materials science because of their unique optical and electronic
properties. For example, TiO 2 -Au and ZnO NPs containing N 3 dye
are useful materials in the fabrication of solar cells, 1,2 fullerene-
functionalized Au NPs are effective in the fabrication of light-
harvesting devices, 3,4 and Au NPs that are conjugated with 5-((2-
(and-3)-S-(acetylmercapto)succinoyl)amion)- luorescein and
5-[1,2]dithiolan-3-ylpentanoic acid and 1,6-bis(( N -carbazol-3-
yl)methyl)-2,4-hexadiyne ester are useful in the preparation of light
emitting devices. 5,6
Noble metal NPs are among the most polarizable inorganic
templates capable of producing enhanced optical ields near their
surfaces under visible electromagnetic radiation. When located in
close proximity to a metallic NP, a dye undergoes strong changes in
its electronic and optical properties likely as a result of a mixing of
the molecule and metal electronic levels as well as an interaction
of the molecule with the surface plasmon resonance. The changes
are dependent on several parameters, including the size and species
of the NPs, the distance between the luorophores and the metal
surface, the roughness of the metal surface, and the orientation
of the luorophore transition moment. Fluorescence quenching
occurs in the case of the adsorption of a dye on a metal surface
while a luorescence enhancement occurs when the dye is located at
distances between 70 and 100 Å from the metal surface. Quenching
provides nonradiative pathways to the ground state but does not
induce signiicant changes to the radiative decay rate. In contrast,
changes in the radiative rates may arise from the interactions of
luorophores with nearby particles through the interactions of
the incident light and the luorophore's oscillating dipole with
the nearby metal surface, leading to increased luorescence. The
luorescence enhancement of the luorophores on the metal surface
is called surface enhanced luorescence (SEF). Researchers have
 
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