Influence of Gold Metallodielectric Partial-Shell Geometrical Irregularities on Dark Plasmon Resonances

The geometric asymmetry of real, fabricated gold partial shells leads to orientation and gold partial coverage dependent local fields and scattering. We illustrate this with single-particle measurements and finite element calculations. In particular, we show that the position and number of well-defined protrusions on the edge of a partial shell qualitatively change the spectra. The metallic protrusions result in geometrical asymmetry, which leads to excitation of the optically dark quadrupole mode as a function of incident light excitation and polarization. The far-field scattering peaks result from the bright dipole resonance with contribution from the dark resonance in the presence of the partial-shell surface protrusions. With more dark modes, the overall scattered intensity decreases, reflecting the energy trapped in the local electric fields of the dark modes, until it ultimately dissipates in the metal

Plasmonic Coupling and Long-Range Transfer of an Excitation along a DNA Nanowire

We demonstrate an excitation transfer along a fluorescently labeled dsDNA nanowire over a length of several micrometers. Launching of the excitation is done by exciting a localized surface plasmon mode of a 40 nm silver nanoparticle by 800 nm femtosecond laser pulses <i>via</i> two-photon absorption. The plasmonic mode is subsequently coupled or transformed to excitation in the nanowire in contact with the particle and propagated along it, inducing bleaching of the dyes on its way. <i>In situ</i> as well as <i>ex situ</i> fluorescence microscopy is utilized to observe the phenomenon. In addition, transfer of the excitation along the nanowire to another nanoparticle over a separation of 5.7 μm was clearly observed. The nature of the excitation coupling and transfer could not be fully resolved here, but injection of an electron into the DNA from the excited nanoparticle and subsequent coupled transfer of charge (Dexter) and delocalized exciton (Frenkel) is the most probable mechanism. However, a direct plasmonic or optical coupling and energy transfer along the nanowire cannot be totally ruled out either. By further studies the observed phenomenon could be utilized in novel molecular systems, providing a long-needed communication method between molecular devices