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We present a study of the interband and intersubband transitions in mixed type I and type II GaAs/AlAs superlattices. Depending on the energy and intensity of the exciting (laser) radiation, either excitons in the wide GaAs wells or separate 2DEG and 2DHG are formed in the wide and narrow GaAs wells, respectively. We observe both the direct interband transitions and the inter-well transitions, and identify them by comparison with the calculated conduction and valence subband dispersion relations and resulting spectra. Intersubband transitions of the photoexcited 2DEG are observed as well. Under the application of an external magnetic field, the interband transitions between electron and hole Landau levels are shown to be strongly dependent on the density of the photoexcited 2DEG.

This paper reports on the improved fabrication process and the optical characterization of different nano-hole arrays in thin metal films that are to be integrated into a novel atto-litre titre plate device for high-speed molecular analysis, such as DNA hybridizations and protein immunoassays. The optical detection is based on the enhanced optical transmission that was recently discovered when light passes through periodically distributed sub-wavelength apertures in optically thick metal films. The transmitted light has also small angular diffraction and well-defined spectral features. Using electron-beam (e-beam) lithography (EBL) and lift-off technique, various array structures with hole diameters ranging between 100 nm and 200 nm and different pitches were fabricated in a 200-nm thick layer of gold (Au), palladium (Pd), and gold/palladium (Au/Pd = 60/40) alloy on glass. Introducing Pd to Au, the grain size of the material is decreased, getting a more well-defined shape of the holes. The transmitted spectrum was measured through periodically and randomly distributed nano-holes in Au. Transmitted spectra were compared as well through similar subwavelength hole arrays in Au, Pd, and Au/Pd alloy. Moreover, the fluorescence of Rhodamine G6 (0.05 µM) was measured when using the transmitted light through periodical cavities in Au as the illumination source. It reveals a nine-fold increase in the fluorescent signal.

Quantitative analysis can be used in combination with fluorescence microscopy. Although the human eye is able to obtain good qualitative results, when analyzing the spatial organization of telomeres in interphase nuclei, there is a need for quantitative results based on image analysis.We developed a tool for analyzing three‐dimensional images of telomeres stained by fluorescence in situ hybridization in interphase nuclei with DNA counterstained with 4′,6‐diamidino‐2‐phenylindole. After deconvolution of the image, we segmented individual telomeres. From the location of the telomeres we derived a distribution parameter ρT, which indicated whether the telomeres were in a disk (ρT ≫ 1) or not (ρT ≈ 1). We sorted mouse lymphocyte nuclei and measured ρT. We also performed a bromodeoxyuridine synchronous cell sorting experiment on live cells and measured ρT at several instances.Measuring ρT for nuclei in G0/G1, S, and G2 produced 1.4 ± 0.1, 1.5 ± 0.2, and 14 ± 2, respectively, showing a significant difference between G2 and G0/G1 or S. For the bromodeoxyuridine synchronous cell sorting experiment, we found a cell cycle dependency of ρT and a correlation between ρT and an observer.In this study we present a quantitative method to characterize the organization of telomeres using three‐dimensional imaging, image processing, and image analysis. © 2005 International Society for Analytical Cytology

Various approaches that were recently developed demonstrate the ability to simultaneously detect all human (or other species) chromosomes by using combinatorial labeling and fluorescence in situ hybridization (FISH). With the growing interest in this field, it is important to develop tools for optimizing and estimating the accuracy of different experimental methods. We have analyzed the principles of multiple color fluorescence imaging microscopy. First, formalism based on the physical principles of fluorescence microscopy and noise analysis is introduced. Next, a signal to noise (S/N) analysis is performed and summarized in a simple accuracy criterion. The analysis assumes shot noise to be the dominant source of noise. The accuracy criterion was used to calculate the S/N of multicolor FISH (M-FISH), spectral karyotyping, ratio imaging, and a method based on using a set of broad band filters. Spectral karyotyping is tested on various types of samples and shows accurate classifications. We have also tested classification accuracy as a function of total measurement time. The accuracy criterion that we have developed can be used for optimizing and analyzing different multiple color fluorescence microscopy methods. The assumption that shot noise is dominant in these measurements is supported by our measurements. Cytometry 35:214–226, 1999. © 1999 Wiley-Liss, Inc.