Correlating Plasmon Polariton Propagation and Fluorescence Enhancement in Single Silver Nanowires

We observe correlation between the length of surface plasmon polariton propagation in silver nanowires and the enhancement of fluorescence intensity due to coupling with localized plasmon resonances. The results of excitation wavelength-dependent fluorescence imaging of CdTe QDs uniformly deposited over silver nanowires indicate the strongest enhancement of fluorescence intensity for wavelengths close to the maximum of localized plasmon resonance, with modest reduction of this effect when the excitation shifts toward longer wavelengths. In contrast, when one of the ends of a silver nanowire is excited with a focused laser, we find a reverse relation for surface plasmon polariton propagation. In fact, the energy propagates most efficiently for the longest excitation wavelength of 635 nm. This inverse correlation points toward an apparent trade-off between electric field confinement and plasmon propagation distance in silver nanowires, introducing thus a limit for efficient remote fluorescence detection when fluorescence enhancement is also desired.