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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