Driven by the demand for ongoing integration and increased complexity of today's microelectronic circuits, smaller and smaller structures need to be fabricated with a high throughput. In contrast to serial nanofabrication techniques, based, e.g., on electron beam or scanning probe methods, optical methods allow a parallel approach and thus a high throughput. However, they rarely reach the desired resolution. One example is plasmon lithography, which is limited by the utilized plasmonic metal structures. Here we show a new approach extending plasmonic lithography with the potential for a highly parallel nanofabrication with a higher level of complexity based on nanoantenna effects combined with molecular nanowires. Thereby femtosecond laser pulse light is converted by Ag nanoparticles into a high plasmonic excitation guided along attached DNA structures. An underlying poly(methyl methacrylate) (PMMA) layer acting as an electron-sensitive resist is so structured along the former DNA position. This apparently DNA-guided effect leads to nanometer grooves reaching even micrometers away from the excited nanoparticle, representing a novel effect of long-range excitation transfer along DNA nanowires.

Certain metal nanoparticles exhibit the effect of localized surface plasmon resonance when interacting with light, based on collective oscillations of their conduction electrons. The interaction of this effect with molecules is of great interest for a variety of research disciplines, both in optics and in the life sciences. This paper attempts to describe and structure this emerging field of molecular plasmonics, situated between the molecular world and plasmonic effects in metal nanostructures, and demonstrates the potential of these developments for a variety of applications.

We showed that the anisotropic disk shape of nanoplasmonic upconverting nanoparticles (NP-UCNPs) creates changes in fluorescence intensity during rotational motion. We determined the orientation by a three-fold change in fluorescence intensity. We further found that the luminescence intensity was strongly dependent on the particle orientation and on polarization of the excitation light. The luminescence intensity showed a three-fold difference between flat and on-edge orientations. The intensity also varied sinusoidally with the polarization of the incident light, with an Imax/Imin ratio of up to 2.02. Both the orientation dependence and Imax/Imin are dependent on the presence of a gold shell on the UCNP. Because the fluorescence depends on the NP’s orientation, the rotational motion of biomolecules coupled to the NP can be detected. Finally, we tracked the real-time rotational motion of a single NP-UCNP in solution between slide and coverslip with diffusivity up to 10−2 μm2s−1.

Tip-enhanced Raman spectroscopy, a combination of Raman spectroscopy and scanning probe microscopy, is a powerful technique to detect the vibrational fingerprint of molecules at the nanometer scale. A metal nanoparticle at the apex of an atomic force microscope tip leads to a large enhancement of the electromagnetic field when illuminated with an appropriate wavelength, resulting in an increased Raman signal. A controlled positioning of individual nanoparticles at the tip would improve the reproducibility of the probes and is quite demanding due to usually serial and labor-intensive approaches. In contrast to commonly used submicron manipulation techniques, dielectrophoresis allows a parallel and scalable production, and provides a novel approach toward reproducible and at the same time affordable tip-enhanced Raman spectroscopy tips. We demonstrate the successful positioning of an individual plasmonic nanoparticle on a commercial atomic force microscope tip by dielectrophoresis followed by experimental proof of the Raman signal enhancing capabilities of such tips.

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.