Abstract

We study the lifetime of two common fluorescent dye molecules from the Alexa Fluor NHS Ester family dissolved in water in an opaque aqueous dispersion of dielectric polystyrene nanoparticles. We investigate the role of the dispersion composition by varying the particle concentration and adding SDS (sodium dodecyl sulfate) surfactant molecules. The observed strong changes in lifetime of Alexa 430 can be attributed to the relative contribution of radiative and non-radiative decay channels while the lifetime of the Alexa 488 dye depends only weakly on the sample composition. For Alexa 430, a dye with a rather low quantum yield in aqueous solution, the addition of polystyrene nanoparticles leads to a significant enhancement in quantum yield and an associated increase of the fluorescent lifetime by up to 55 %. We speculate that the increased quantum yield can be attributed to the hydrophobic effect on the structure of water in the boundary layer around the polystyrene particles in suspension. Adding SDS acts as a quencher. Over a range of particle concentrations the particle induced increase of the lifetime can be completely compensated by adding SDS.

Highlights

  • One of the most important questions in nano-optics and molecular imaging applications is how a point source emits in a complex dielectric environment. This questions lies at the heart of modern quantum optics and it is important for many applications ranging from laser technology [1] to single photon sources [2], solar cells [3] and all varieties of fluorescence spectroscopy and imaging microscopy [4]

  • This is an important result as it shows that in our experiments the dye does not attach to the particle surface as it was claimed to be the case [10] in the context of a previous study of lifetime measurements in polystyrene nanoparticle suspensions using the anionic dye Kiton Red S

  • In the present work we have analyzed the influence of polystyrene nanoparticles in suspension on the decay rate of dissolved dye molecules

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Summary

Introduction

One of the most important questions in nano-optics and molecular imaging applications is how a point source (such as a fluorescent dye molecule) emits in a complex dielectric environment. This questions lies at the heart of modern quantum optics and it is important for many applications ranging from laser technology [1] to single photon sources [2], solar cells [3] and all varieties of fluorescence spectroscopy and imaging microscopy [4]. For example FLIM (fluorescence lifetime imaging microscopy) exploits the fact that a fluorescent molecule has a different lifetime depending on its dielectric environment [4]. Understanding the fluorescent decay in a complex and well controlled dielectric environment is of great importance

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