How the occupied KDEL receptor ERD2 is sorted into COPI vesicles for Golgi-to-ER transport is largely unknown. Here, interactions between proteins of the COPI transport machinery occurring during a "wave" of transport of a KDEL ligand were studied in living cells. FRET between CFP and YFP fusion proteins was measured by multifocal multiphoton microscopy and bulk-cell spectrofluorimetry. Ligand binding induces oligomerization of ERD2 and recruitment of ARFGAP to the Golgi, where the (ERD2)n/ARFGAP complex interacts with membrane-bound ARF1. During KDEL ligand transport, interactions of ERD2 with beta-COP and p23 decrease and the proteins segregate. Both p24a and p23 interact with ARF1, but only p24 interacts with ARFGAP. These findings suggest a model for how cargo-induced oligomerization of ERD2 regulates its sorting into COPI-coated buds.

Three-dimensional photonic crystals with bandgaps of 1.5-2.3 mum in wavelength and with gap/midgap ratios of as much as 18% were generated efficiently by two-photon photopolymerization in a liquid resin. From 0.5-1.1-mW femtosecond-pulsed 540-nm light, woodpile structures consisting of 40 layers of elliptically shaped rods spaced at 350-500 nm were fabricated by focusing with a 1.3-N.A. objective. The high degree of correlation in these structures allowed the suppression of infrared transmission by as much as 50% as well as the observation of higher-order bandgaps. We also investigated the decrease in the gap wavelength on reduction of layer spacing, in-plane rod spacing, and rod size.

The combination of pulsed-mode excitation multifocal multiphoton microscopy with a high-repetition, time-gated intensified CCD camera enables efficient three-dimensional (3D) fluorescence lifetime imaging. With a 200-ps gate opening at 76 MHz repetition rate, fluorescence decay can be traced in a sequence of images with varying delays between pulse and gate. Fluorophore lifetimes are measured with a precision of a few picoseconds. As an application we show that, upon two-photon excitation at 800 nm, certain pollen samples feature a multiexponential fluorescence relaxation. Our results indicate that efficient four-dimensional microscopy with hundreds of nanometer spatial and tens of picoseconds temporal resolution is within reach.

By magnetization induced second harmonic generation (MSHG) the surface magnetization of fcc Fe films on Cu(100) is studied. The tetragonally distorted phase below 4 monolayers (ML) and the relaxed fcc phase above 4 ML can unambigously be distinguished by different average MSHG signals. Nearly constant asymmetry of the second harmonic intensities between 1.3 and 10 ML proves, to a good approximation, thickness independence of the surface magnetization irrespective of the phase transition at 4 ML. The nonlinear Kerr angle amounts to 4 ± . [S0031-9007(96)

This paper provides a photopolymerizing material suitable for stereolithography of complex submicrometer‐sized three‐dimensional (3D) structural elements to a broad scientific public. Here, we present the formulation of a polymer (LN1 resin) that allows further research in the field of nanofabrication and ‐technology as it surpasses current material limitations. The polymer consists of multifunctional acrylate oligomers as binder, polyfunctional monomers, and a photoinitiator (PI). The chemistry to form 3D structures is based on photopolymerization of the acrylate system initiated by free‐radical species that are triggered by two‐photon absorption of a PI. Important parameters of photocuring, such as the effects of PI concentration, temperature, and light intensity, were studied using photocalorimetry. The thermal stability of the material was tested using thermal gravimetric analysis, providing key information for electronic and photonic applications. Photonic‐crystal structures generated from this resin exhibiting photonic stop gaps in near‐infrared‐ and telecommunication‐wavelength regions are presented.