Metal-Enhanced Fluorescence from Chromium Nanodeposits

Over the last several years, our laboratory has described in detail the favorable effects of fluorophores in close proximity to metallic nanoparticles. Metal nanoparticles comprised of gold, silver, copper, and zinc show enhanced fluorescence intensities and photostabilities for fluorophores positioned within 10 nm of the particles. In this paper we show that, in addition to these metals, chromium nanodeposits can also enhance the fluorescence of close proximity fluorophores, with probes such as fluorescein showing a greater than 8-fold enhancement. However, in contrast to gold, silver, and copper nanoparticles, fluorophores in close-proximity to chromium nanodeposits do not display reduced radiative lifetimes, suggesting that an enhanced electric field component (enhanced excitation rate) is the dominate mode of emission enhancement, similar to recent work by our laboratory for zinc nanoparticles. In addition, we also show the metal-sandwich geometries used in previous metal-enhanced fluorescence studies can give erroneous enhanced fluorescence readings, if care is not taken to normalize the excitation intensity/irradiance.