Fluorophore-Induced Plasmonic Current in Metal Nanoparticle Island Films

Abstract

Fluorophore-induced plasmonic current is generated when an excited fluorophore in proximity to a metal nanoparticle island film non-radiatively transfers energy to the metal, inducing a measurable change in electrical current through the film. This induced electrical signal is found dependent on the magnitude of the fluorophore extinction coefficient and quantum yield. In other words, the electrical signal contains photophysical information pertaining to the fluorophore. This signal holds potential for a molecular fingerprint of the fluorophore, leading to the direct detection of fluorescence without the need for traditional detectors such as photomultiplier tubes and charge coupled devices. Fluorophore-induced plasmonic current has been found dependent on several properties of the system including nanoparticle size and spacing in the film. This is explained by an increased nanoparticle capacitance in relatively large and closely spaced particles, allowing for increased electron transport through the film upon fluorophore excitation. Bringing the metal nanoparticles very close together in the film has also been found to decrease Metal-Enhanced Fluorescence (MEF) emission, with a subsequent increase in the fluorophore induced current. The induced current has also been found dependent on the applied voltage and film temperature. This allows for optimization of the induced signal through controlling for these properties of the system. In addition, fluorophore labelled albumin protein has been quantitated on a film surface, allowing for an estimation of the current change generated per protein and per fluorophore tag molecule. Finally, a model protein binding assay has been constructed, utilizing the strong interaction between biotin and streptavidin to bring a fluorophore label into proximity of a metal nanoparticle island film, with subsequent detection via the fluorophore induced current.