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:

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