(633a) Fluorescence Quenching of CdSe/ZnS Nanocrystals near Copper Nanoparticles in Aqueous Solution

Fluorescence quenching of CdSe/ZnS nanocrystals near
copper nanoparticles in aqueous solution

Quenching of fluorescence of vicinal fluorophores
of nanoparticles is efficiently utilized for many different applications such
as improvement of homogeneous and competitive fluorescence immunoassay, optical
detection of DNA hybridization, competitive hybridization assay and in
optoelectronics^1-3.  Metal nanoparticles
are known to both quench and enhance fluorescence depending on the optical
properties of nanoparticles, fluorophore-particle separation distance,
molecular dipole orientation with respect to particle surface and size of the
nanoparticles.  The presence of nanoparticles close to the luminophores can
create new nonradiative channels due to light absorption inside the metal, thus
quenching the emission of luminophores ⁴.  If the probe
molecules are very close to the nanoparticles (typically, less than 5 nm),
luminescence emission is quenched due to Forster transfer of energy from the
excited state of the molecule to the surface plasmons of the metal surface. Metal
quenched fluorescence has been studied mostly using gold nanoparticles^{1, 2, 5}.

In this present study, we investigate the fluorescence
quenching of  CdSe/Zns nanocrystals in  the presence of copper nanoparticles.  Copper
nanoparticles coated with stabilizing polyvinylpyrrolidone (PVP) polymer,
quench the fluorescence of CdSe/Zns nanocrystals coated with mercaptoundecanoic
ligands.  Stable copper nanoparticle colloid was synthesized by reducing copper
salt precursor using ascorbic acid in the presence of PVP.  The fluorescence
quenching of the CdSe/Zns nanocrystals follows the Stern-Volmer relations
against concentration of the copper nanoparticles in water with a detection
limit of 5 nanomol.  The mechanism of the fluorescence quenching on the copper
nanoparticles surfaces has been treated in the light of electromagnetic
interaction between nanoparticles and fluorophores which influences both
radiative and non-radiative decay rate of fluorophores.  We presented theoretical
calculation using Gersten-Nitzan (GN) model⁶ to
provide insight into the influence of the Cu nanoparticles on radiative and non-radiative
decay rates of luminophore molecules at their close proximity.

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