Fluorophore-Induced Plasmonic Current from Copper and Silver Mixed-Metal Films

In recent years, our laboratory has demonstrated that excited-state fluorophores can nonradiatively couple through space to noble metal nanoparticles. If the noble metal nanoparticles are isolated, both highly photostable and enhanced fluorescence can be observed, a phenomenon known as metal-enhanced fluorescence (MEF). However, if the nanoparticles are spaced relatively much closer together, the coupled quanta can now “hop” between the nanoparticles, ultimately producing a current across the nanoparticle film. The magnitude of this fluorophore-induced plasmonic current (FIPC) is a function of how far apart both the donor (fluorophore) and acceptor (nanoparticle) are spaced; the excitation polarization and, importantly, the degree of overlap between the fluorophores’ emission spectrum with that of the nanoparticles plasmon absorption. All of the work to date on FIPC has paired the plasmon absorption wavelengths with those of the emission of an appropriate fluorophore, which ultimately leads to nanoparticle films that can produce current over narrow wavelength ranges. In this paper, we demonstrate that mixed-metal substrates composed of both Cu and Ag nanoparticles can significantly broaden the wavelength range over which multiple fluorophores from the ultraviolet (UV) to the red part of the visible spectrum can both couple and induce plasmonic current.