(419c) Composition Effect of Ag-Cu Alloy Nanoparticles On Luminescence Enhancement/Quenching of Vicinal Luminophores

Composition effect of Ag-Cu alloy nanoparticles on
luminescence enhancement/quenching of vicinal luminophores

The emission of luminophores is significantly influenced at
the close proximity of conducting metallic nanostructures.  Metal nanoparticles
are known to both quench and enhance luminescence depending on the optical
properties of nanoparticles, fluorophore-particle separation distance,
molecular dipole orientation with respect to particle surface and size of the
nanoparticles^1,
2. 
Both enhancement and quenching of luminescence due to the proximity of
nanoparticles are efficiently utilized for many different applications. 
Enhanced signal and photostability of luminophores, improved surface
immunoassay and DNA detection, enhanced wavelength-ratiometric sensing, and
amplified assay detection are few examples of the applications of metal
enhanced luminescence^3,
4. 
On the other hand, quenching resulting due to metallic nanoparticles is
successfully utilized for the improvement of homogeneous and competitive
fluorescence immunoassay, optical detection of DNA hybridization, competitive
hybridization assay and in optoelectronics^5,
6. 

In this work, metal
enhanced/quenched luminescence was explored in the vicinity of Ag_xCu_100-x
alloy nanoparticles at different compositions (x=100, 67, 50, 30 and 0).  These
Ag-Cu nanoparticles were synthesized using the polyol process.  It was observed
that the luminescence of dyes was strongly dependent on the Ag-Cu nanoparticle
composition.  Highest luminescence enhancement of dye Cy 3, commonly used for
biological applications, was realized at the vicinity of pure silver
nanoparticles.  Enhancement effects were found to decrease as the percentage of
copper increases in the nanoparticles, leading to the quenching of fluorescence
at the pure copper nanoparticle platform.  Theoretical calculations based on
the corrected Gersten and Nitzan model ⁷ were carried out to predict the
possible enhancement factors for spherical Ag-Cu nanoparticles for a range of
compositions.  Results of these calculations corroborate the experimental
findings.  Signal manipulation of luminescent dyes using the composition of
alloy nanoparticles will extend applications of metal enhanced luminescence to
several fields ranging from optoelectronics to biological research.

References:

(1)        Lakowicz, J. R.; Shen, Y.; D'Auria, S.; Malicka, J.; Fang, J.; Gryczynski,
Z.; Gryczynski, I. Anal. Biochem. 2002, 301, 261-277.

(2)        Anger,
P.; Bharadwaj, P.; Novotny, L. Phys. Rev. Lett. 2006, 96,
113002-113001-113004.

(3)        Zhang,
J.; Matveeva, E.; Gryczynski, I.; Leonenko, Z.; Lakowicz, J. R. J. Phys.
Chem. B 2005, 109, 7969-7975.

(4)        Lakowicz,
J. R. Anal. Biochem. 2001, 298, 1-24.

(5)        Zai-Sheng,
W.; Jian-Hui, J.; FU, L.; Guo-Li, S.; Ru-Qin, Y. Anal. Biochem. 2006,
353, 22-29.

(6)        Ao,
L.; Gao, F.; Pan, B.; He, R.; Cui, D. Anal. Chem. 2006, 78,
1104-1106.

(7)        Mertens,
H.; Koenderink, A. F.; Polman, A. Phys. Rev. B 2007, 76,
115123-115121-115112.