Plasmonically Enhanced Electron Escape from Gold Nanoparticles and Their Polarization-Dependent Excitation Transfer along DNA Nanowires

Here we show plasmon mediated excitation transfer along DNA nanowires over up to one micrometer. Apparently, an electron excitation is initiated by a femtosecond laser pulse that illuminates gold nanoparticles (AuNP) on double stranded DNA (dsDNA). The dependency of this excitation on laser wavelength and polarization are investigated. Excitation of the plasmon resonance of the AuNPs via one- and two-photon absorption at 520 and 1030 nm, respectively, was explored. We demonstrate an excitation transfer along dsDNA molecules at plasmon supported four-photon excitation of AuNP cluster or at laser field driven nanoparticle electron tunneling for an alignment of the attached dsDNA to the polarization of the electric field of the laser light. These results extend the previously observed plasmonically induced three-photon excitation transfer along DNA nanowires to another nanoparticle material (gold) and the adapted irradiation wavelengths

Tuning of Spectral and Angular Distribution of Scattering from Single Gold Nanoparticles by Subwavelength Interference Layers

Localized surface plasmon resonance (LSPR) as the resonant oscillation of conduction electrons in metal nanostructures upon light irradiation is widely used for sensing as well as nanoscale manipulation. The spectral resonance band position can be controlled mainly by nanoparticle composition, size, and geometry and is slightly influenced by the local refractive index of the near-field environment. Here we introduce another approach for tuning, based on interference modulation of the light scattered by the nanostructure. Thereby, the incoming electric field is wavelength-dependent modulated in strength and direction by interference due to a subwavelength spacer layer between nanoparticle and a gold film. Hence, the wavelength of the scattering maximum is tuned with respect to the original nanoparticle LSPR. The scattering wavelength can be adjusted by a metallic mirror layer located 100–200 nm away from the nanoparticle, in contrast to near-field gap mode techniques that work at distances up to 50 nm in the nanoparticle environment. Thereby we demonstrate, for the first time at the single nanoparticle level, that dependent on the interference spacer layer thickness, different distributions of the scattered signal can be observed, such as bell-shaped or doughnut-shaped point spread functions (PSF). The tuning effect by interference is furthermore applied to anisotropic particles (dimers), which exhibit more than one resonance peak, and to particles which are moved from air into the polymeric spacer layer to study the influence of the distance to the gold film in combination with a change of the surrounding refractive index