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Metallic nanorod antennas can be considered as an analogue to classical half-wave dipole antennas, constituting an important tool for manipulating linear and nonlinear light-matter interactions in nanoscale volumes. Using two-photon luminescence (TPL) scanning laser microscopy, we investigate such optical antennas beyond their fundamental dipole mode. The antenna mode dispersion is extracted from the nonlinear TPL measurement and reveals a TPL process that is dominated by plasmon-induced enhancement of the two-photon absorption in the metal. Additionally, a clear signature of the mode parity is observed in the TPL images. TPL maxima are observed outside the antenna boundaries for even parity modes, whereas they are located inside for odd modes. It is concluded that for even modes the two-photon luminescence emission is strongly mediated by retardation of the excitation field, a consequence of their zero net-dipole moment. This selective excitation of different mode parities is highly relevant for nanoscal...

Using two-photon luminescence (TPL) scanning laser microscopy and FDTD simulations, we investigate the TPL process of Au nanoantennas beyond the fundamental mode. Enhanced two-photon absorption dominates the process and a clear signature of the mode parity is observed.

Single particle tracking (SPT) of transmembrane receptors in the plasma membrane often reveals heterogeneous diffusion. A thorough interpretation of the displacements requires an extensive analysis suited for discrimination of differentmotion types present in the data. Here the diffusion pattern of the homomeric α3-containing glycine receptor (GlyR) is analyzed in themembrane of HEK 293 cells. More specifically, the influence of the α3 RNA splice variants α3K and α3L on lateralmembrane diffusion of the receptor is revealed in detail. Using a combination of ensemble and local SPT analysis, free and anomalous diffusion parameters are determined. The GlyR α3 free diffusion coefficient is found to be 0.13 ± 0.01 μm2/s and both receptor variants display confined motion. The confinement probability level and residence time are significantly elevated for the α3L variant compared to the α3K variant. Furthermore, for the α3L GlyR, the presence of directed motion was also established, with a velocity matching that of saltatory vesicular transport. These findings reveal that α3 GlyRs are prone to different types of anomalous diffusion and reinforce the role of RNA splicing in determining lateral membrane trafficking. This work was funded by the Research Council of the UHasselt, tUL. GlyR expression constructs were obtained thanks to funding by the Helmholtz Association (VH-NG-246 to J.C.M.) and the Bundesministerium fur Bildung und Forschung BMBF (Era-Net NEURON II CIPRESS to J.C.M.). The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Program (FP7/2007-2013)/ERC Grant Agreement no 291593 FLUOROCODE), from the Flemish government in the form of long-term structural funding "Methusalem" grant METH/08/04 CASAS, from the 'Fonds voor Wetenschappelijk Onderzoek Vlaanderen' (FWO grants G.0197.11; G0484.12,) and from the Hercules Foundation (HER/08/021). S.R., J.H. and M.A. thank the Federal Science Policy of Belgium (IAP-VI/27). The support by the FWO-onderzoeksgemeenschap "Scanning and Wide Field Microscopy of (Bio)-organic Systems" is gratefully acknowledged by J.H. and M.A.

Fluorescence recovery after photobleaching (FRAP) is a common technique to probe mobility of fluorescently labeled proteins in biological membranes by monitoring the time-dependence of the spatially integrated fluorescence signals after a bleaching pulse. Discrimination by FRAP between free diffusion with an immobile fraction (FDIM) and the phenomenological model for anomalous diffusion based on the time-dependent diffusion coefficient (TDDC) is a challenging problem, requiring extremely long observation times for differentiation. Recently, rectangular FRAP (rFRAP) has been introduced for normal diffusion by considering not only the temporal but also spatial information, taking the effective point spread function of the optical system into account. In this work we provide an extension of rFRAP toward anomalous diffusion according to the continuous time random walk (CTRW). We explore whether the spatial information in rFRAP allows for enhanced discrimination between FDIM, TDDC, and CTRW in a single experiment within a feasible time window. Simulations indicate that rFRAP can indeed differentiate the different models by evaluating the spatial autocorrelation of the differences between the measured and fitted pixel values. Hence, rFRAP offers a tool that is capable of discriminating different types of diffusion at shorter time scales than in the case where spatial information is discarded.

We report our latest results on second harmonic generation (SHG) microscopy from arrays of G-shaped chiral gold nanostructures. The nanostructures are arranged in unit cells composed of four Gs, each rotated at 90° with respect to its neighbors. As it has already been demonstrated, for linearly polarized light, these unit cells yield a pattern of four SHG hotspots. However, upon increasing the pitch of the nanostructured arrays, extra hotspots can be observed at the edges of the unit cells. While the origin of these extra hotspots remains to be elucidated, their position indicates a relationship to coupling behavior between the unit cells.

In response to the incident light's electric field, the electron density oscillates in the plasmonic hotspots producing an electric current. Associated Ohmic losses raise the temperature of the material within the plasmonic hotspot above the melting point. A nanojet and nanosphere ejection can then be observed precisely from the plasmonic hotspots.

4–6 ] In such devices, light waves would be used instead of electrons. The possibility arises from the fact that light waves can couple to collective excitations of electrons at the surfaces of metallic nanostructures, a prop-erty referred to as surface plasmon resonance. Because these optically induced resonances occur at the surfaces and interfaces of the nanostructures, they can readily be investigated with a surface- and interface-specifi c optical technique, such as second-harmonic generation (SHG). SHG is a nonlinear optical technique that, within the dipole approximation, is forbidden in materials with a center of symmetry. Consequently, SHG is highly sensitive to regions with broken symmetry, such as surfaces (or interfaces), and it has been successfully applied to the study of plasmonic nano-materials with different geometries.

We have applied the surface sensitive nonlinear optical technique of magnetization induced second harmonic generation. (MSHG) to plasmonic, magnetic nanostructures made of Ni. We show that surface plasmon contributions to the MSHG signal can reveal the direction of the magnetization. Both the plasmonic and the magnetic nonlinear optical responses can be tuned; our results indicate novel ways to combine nanophotonics, nanoelectronics, and nanomagnetics and suggest the possibility for large magneto-chiral effects in metamaterials. ispartof: ACS Nano vol:5 issue:1 pages:91-96 ispartof: location:United States status: published

Many membrane proteins and lipids are partially confined in substructures ranging from tens of nanometers to micrometers in size. Evidence for heterogeneities in the membrane of oligodendrocytes, i.e. the myelin-producing cells of the central nervous system, is almost exclusively based on detergent methods. However, as application of detergents can alter the membrane phase behaviour, it is important to investigate membrane heterogeneities in living cells. Here, we report on the first investigations of the diffusion behavior of the myelin-specific protein MOG (myelin oligodendrocyte glycoprotein) in OLN-93 as studied by the recently developed RICS (raster-scanning image correlation spectroscopy) technique. We implemented RICS on a standard confocal laser-scanning microscope with one-photon excitation and analog detection. Measurements on FITC-dextran were used to evaluate the performance of the system and the data analysis procedure.

While it has been demonstrated that, above its resolution limit, Second Harmonic Generation (SHG) microscopy can map chiral local field enhancements, below that limit, structural defects were found to play a major role. Here we show that, even below the resolution limit, the contributions from chiral local field enhancements to the SHG signal can dominate over those by structural defects. We report highly homogeneous SHG micrographs of star-shaped gold nanostructures, where the SHG circular dichroism effect is clearly visible from virtually every single nanostructure. Most likely, size and geometry determine the dominant contributions to the SHG signal in nanostructured systems. (C) 2011 Optical Society of America ispartof: Optics Express vol:20 issue:1 pages:256-264 ispartof: location:United States status: published