Tip-enhanced near-field optical images and correlated topographic images of an organic semiconductor film (diindenoperylene, DIP) on Si have been recorded with high optical contrast and high spatial resolution (17 nm) using a parabolic mirror with a high numerical aperture for tip illumination and signal collection. The DIP molecular domain boundaries being one to four molecular layers (1.5-6 nm) high are resolved topographically by a shear-force scanning tip and optically by simultaneously recording the 6x10{5} times enhanced photoluminescence (PL). The excitation is 4x10{4} times enhanced and the intrinsically weak PL-yield of the DIP-film is 15-fold enhanced by the tip. The Raman spectra indicate an upright orientation of the DIP molecules. The enhanced PL contrast results from the local film morphology via stronger coupling between the tip plasmon and the exciton-polariton in the DIP film.

Abstract. Calf thymus DNA adsorbed on a rough gold substrate or on an atomically smooth gold (111) surface has been investigated by collecting its unique Raman fingerprints using either surface-enhanced Raman scattering (SERS) or tip-enhanced Raman scattering (TERS). A monolayer coverage of DNA strands adsorbed at both the irregular rough edges of evaporated gold grids and at gold nanoparticles is detected by SERS. Highly improved sensitivity down to single DNA strand spectroscopic determination is accomplished by TERS providing an enhancement factor of at least 1400. Based on our experimental results, we propose that TERS is a promising technique to study the DNA-drug molecule interaction on the level of a single DNA strand.

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In this paper gold nanorings (NRs) are applied as particularly well-suited sensing elements for mapping the radially symmetric electric fields in the high numerical aperture focus of cylindrical vector beams. The optical properties of gold nanorings are analyzed by a combination of extinction and single particle dark field spectroscopy as well as confocal photoluminescence (PL) imaging. The results are compared to numerical calculations. The in-plane components in the focus of the cylindrical vector beams are estimated through the PL intensity distributions of the NRs. The optimum overlap between the structure and excitation is visualized by a narrow centre spot in the far-field PL scan.