A new means of switching the fluorescence emission of a single nanocrystal by intervention of a gold‐modified AFM tip, and the luminescence properties (see TIRFM image) as a function of distance between the single quantum dot and the tip, are presented. Significant luminescence enhancement due to exciton–plasmon coupling was detected. This is important in controlling molecular individuals with applications ranging from microarrays to manipulation of single reporter molecules. TIRFM: Total‐internal‐reflection fluorescence microscopy.

We describe an optical detection technique that delivers high signal-to-noise discrimination to enable a multi-parameter flow cytometer that combines high performance, robustness, compactness and low cost. The enabling technique is termed “spatially modulated detection” and generates a time-dependent signal as a continuously fluorescing (bio-) particle traverses an optical transmission pattern along the fluidic channel. Correlating the detected signal with the expected transmission pattern achieves high discrimination of the particle signal from background noise. Additionally, the particle speed and its fluorescence emission characteristics are deduced from the correlation analysis. Our method uses a large excitation/emission volume along the fluidic channel in order to increase the total flux of fluorescence light that originates from a particle while requiring minimal optical alignment. Despite the large excitation/detection volume (~ 1mm), the mask pattern enables a high spatial resolution in the micron range. This allows for detection and characterization of particles with a separation (in flow direction) comparable to the dimension of individual particles. In addition, the concept is intrinsically tolerant of non-encoded background fluorescence originating from fluorescent components in solution, fluorescing components of the chamber and contaminants on its surface. The optical detection technique is illustrated with experimental results on multi-color detection with a single large area detector by filtering fluorescence emission of different particles through a patterned color mask. Thereby the particles’ fluorescence emission spectrum is encoded in a time dependent intensity signal and color information can be extracted from the correlation analysis. The multicolor detection technique is demonstrated by differentiation of micro-beads loaded with PE and PE-Cy5 that are excited at 532 nm.

The 200,000-dalton neurofilament subunit (P200) and the 160,000-dalton (P160) and 78,000-dalton (P78) neurofilament subunits were partially purified from bovine brain. Intact neurofilaments were prepared by high-speed and sucrose-zone centrifugation . The crude neurofilament was solubilized in 8 M urea solution containing pyridine, formic acid, and 2-mercaptoethanol . The solubilized neurofilament was purified by carboxymethyl (CM) cellulose column and hydroxylapatite column chromatography . The P200 was purified as separate from P160 and P78, but the P160 and P78 subunits were copurified on CM cellulose, hydroxylapatite, Bio-Gel A150m, and Sephadex G-150 column chromatography . Electron microscopy of these purified neurofilament subunits revealed the P200 subunit as a globular structure, and the P160 and P78 subunits as a rod-shaped structure extending up to 120 nm with a 8-to 12-nm width. In the presence of 200 mM KCI, 15 mM M9Cl 2, and 1 mM ATP, the purified subunits assembled into long filaments . Under the assembly condition, P160 and P78 subunits elongated up to 500 nm, but the longer filament formation required the presence of P200 subunits . The filaments formed in vitro were of two types: long straight filaments and intertwined knobby-type filaments. From these results, we have suggested that P160 and P78 form the neurofilament backbone structure and P200 facilitates the assembly of the backbone units into longer filaments .The neurofilament is a 10-nm filament specific to neurons of the central and peripheral nervous system (5) . The neurofilament from vertebrates seems to be composed of three unidentical polypeptide subunits of 200,000, -160,000 and 68,000 daltons (2,4,7,11,13,16) . However, other 10-nm filaments present in nonneuronal cells and invertebrate neurons seem to be composed of only one or two subunits (5) . Studies on the neurofilament have been mainly directed toward the identification and characterization of these subunits . Studies on the neurofilament-assembly mechanism require purified individual neurofilament subunits . Recently, Willard et al. (20) purified 200,000-dalton neurofilament subunit from rabbit and others have used individual neurofilament subunit polypeptides eluted from polyacrylamide gel slabs for immunological studies . Neurofilament subunits obtained in these ways may not be suitable for studies of neurofilament assembly in terms of both quality and/or quantity.We have made efforts to purify neurofilament subunits from calf brain and report in this communication the methods for 560 solubilization ofneurofilament, the partial purification of subunits, and the results of studies of their assembly. MATERIALS AND METHODS Preparation of NeurofilamentsCrude neurofilament was prepared by use of a modified procedure of Runge et al. (15) and Mori and Kurokawa (13). Fresh bovine brains were obtained from a local beef purveyor and homogenized for 2 min in a Waring blender in 1 vol (wt/vol) of 0.1 M MES (2[N-morpholino]ethane sulfonic acid) buffer, pH 6.6, containing 0...

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A novel hyperspectral imaging system has been developed that takes advantage of the tunable path delay between orthogonal polarization states of a liquid crystal variable retarder. The liquid crystal is placed in the optical path of an imaging system and the path delay between the polarization states is varied, causing an interferogram to be generated simultaneously at each pixel. A data set consisting of a series of images is recorded while varying the path delay; Fourier transforming the data set with respect to the path delay yields the hyperspectral data-cube. The concept is demonstrated with a prototype imager consisting of a liquid crystal variable retarder integrated into a commercial 640x480 pixel CMOS camera. The prototype can acquire a full hyperspectral data-cube in 0.4 s, and is sensitive to light over a 400 nm to 1100 nm range with a dispersion-dependent spectral resolution of 450 cm(-1) to 660 cm(-1). Similar to Fourier transform spectroscopy, the imager is spatially and spectrally multiplexed and therefore achieves high optical throughput. Additionally, the common-path nature of the polarization interferometer yields a vibration-insensitive device. Our concept allows for the spectral resolution, imaging speed, and spatial resolution to be traded off in software to optimally address a given application. The simplicity, compactness, potential low cost, and software adaptability of the device may enable a disruptive class of hyperspectral imaging systems with a broad range of applications.