Tina Züchner

We use raster-scanning confocal microscopy in combination with radially and azimuthally polarized laser excitation for mapping the three-dimensional (3D) orientation of individual spatially isolated gold nanorods (GNRs). The simultaneous acquisition of both the elastic scattering patterns and the one-photon luminescence patterns of the same GNR allows for determining both the particle position and the orientation with high precision. By analyzing experimental patterns and comparing them to theoretical results obtained by computer simulations, we establish a complete 3D photoluminescence map of single GNRs. Both elastic scattering and luminescence patterns of the same particle are found to display modifications of the refractive index of the dielectric environment. The polarization dependence of GNRs photoluminescence suggests a plasmon-mediated process.

We present a powerful technique to fully characterize individual gold nanorods by using confocal microscopy in combination with higher order laser modes. We obtain topological information far beyond the optical resolution limit, although the used method is diffraction limited. We perform, for the first time, the imaging of gold nanorods by recording simultaneously their scattering and luminescence signal. In the future, this might permit to extent the results achieved already in [1] to a 3D system. Moreover, the scattering pattern is strongly dependent on the phase relation between the light scattered and reflected at the sample interface, while the luminescence pattern does not depend on this phase relation. By exploiting an index matched sample geometry, we were able to omit the phase relation and therefore detect the pure scattering signal and qualitatively compare it with the luminescence one. Furthermore, as previously shown [2, 3], our technique is capable to track the rotation of single noble metal nanorods. We show that measuring the rotation rate of gold nanorods might be useful to estimate the local viscosity of the surrounding medium.

Higher order laser modes, mainly called doughnut modes (DMs) have use in many different branches of research, such as, bio‐imaging, material science, single‐molecule microscopy, and spectroscopy. The main reason of their increasing importance is that recently, the techniques to generate well‐defined DMs have been refined or rediscovered. Although their potential is still not fully utilized, their specifically polarized field distribution gives rise to a wide field of applications. They are contributing to complete our fundamental knowledge of the optical properties of single emitting species, such as molecules, nanoparticles, or quantum dots, offering insight into the three‐dimensional dipole or particle orientation in space. The perfect zero intensity in the focus center qualifies some DMs for stimulated emission depletion (STED) microscopy. For the same reason, they have been suggested for trapping and tweezing applications.

We study spatially isolated, individual gold nanorods placed at a planar interface between two dielectric media using confocal interference scattering microscopy in combination with higher order laser modes. Approaching refractive index matching conditions, we observe that the elastic scattering patterns of individual nanorods exhibit an exponential increase of both the scattering intensity and the signal-to-background ratio. In case refractive index matching conditions are fullfilled, the data acquisition rates are maximized and suitable for in-vivo biological measurements. In all cases, the characteristic two-lobe shape of the scattering patterns of single nanorods remains unchanged while the sign of the image contrast is a direct consequence of the refractive index variation occurring at the interface.

Summary: We demonstrate a novel optical method for characterizing single Au nanoparticles by acquiring their scattering patterns. This technique combines confocal microscopy and higher‐order laser modes for detecting the light scattered by sub‐wavelength–sized nanoobjects. The optical patterns are generated by the coherent superposition of the field scattered by individual metallic particles and the excitation field reflected at the cover slide–air interface and provide information about the particles' position, orientation, size and shape. Detectable changes in the full width at half maximum (FWHM) of the signal intensity permit to distinguish between 20‐ and 60‐nm diameter Au spheres. The confocal images are also very sensitive to the particle's geometry and polarizability, that is, Au nanospheres, Au nanorods and triangular Au nanoplates give different characteristic patterns if the excitation wavelength is varied.

We used confocal interference scattering microscopy combined with higher order laser modes to determine the position, the shape, the orientation and the effect of the environment on individual metal nanoparticles by studying their scattering patterns.

We present a novel scattering microscopy method to detect the orientation of individual silver nanorods and to measure their relative distances. Using confocal microscopy in combination with either the fundamental or higher order laser modes, scattering images of silver nanorods were recorded. The distance between two individual nanorods was measured with an accuracy in the order of 1 nm. We detected the orientation of isolated silver nanorods with a precision of 0.5 degree that corresponds to a rotational arch of about 1 nm. The results demonstrate the potential of the technique for the visualization of non-bleaching labels in biosciences.