Microcontact printing (µCP) is a versatile soft-lithographic technique to pattern substrates using an elastomeric stamp. We demonstrate the high-resolution capabilities of this technique for the fabrication of metal nanowires using either subtractive or additive patterning strategies. The subtractive method relies on printing a self-assembled monolayer (SAM) to protect a metal substrate selectively in a wetchemical etch process. We applied this approach to pattern Au, Ag, Cu, and Pd using eicosanethiol (ECT), and Al by printing hexadecanephosphonic acid (HDPA) as the resist-forming compound. As the etch process has to be selective and reliable, optimization of the etch chemistries is essential to obtain nanowires with excellent lithographic definition. The additive method involves the formation of wire template structures that can direct the electroless deposition (ELD) of a metal on a substrate. One variation of this approach entailed the patterning of a thin Au layer that was printed and etched to initiate ELD of Ag, Cu, and NiWP. Printing a colloidal Pd/Sn catalyst directly onto a substrate constitutes another variation of this patterning strategy. The use of a defined colloidal suspension as the ink, the derivatization of the stamp with poly-(ethylene glycol) (PEG), and the pretreatment of the substrate with an amino-functionalized silane were the key elements of this approach, which was demonstrated for the fabrication of NiB and CoP nanowires. Devices with arrays consisting of 400-µm-long wires with 1 µm pitch were produced with these patterning strategies, and wire dimensions of 150-500 nm in width were achieved depending on the fabrication parameters. We have characterized the resulting nanowires using atomic force microscopy (AFM), determined their morphological properties, and addressed their electrical performance.

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The processes taking place during routine chromosome preparation are not well understood. In this study, the morphological changes in amniotic fluid cells, blood lymphocytes, and bone marrow cells in the metaphase stage were examined under an inverted microscope during chromosome preparation. The putative processes that occur during chromosome preparation were simulated in suspension, and the cells were treated with different mixtures of hypotonic solution, fixative, methanol, acetic acid, and water. Evaporation of the fixative was performed under normal atmospheric conditions and under vacuum at different levels of humidity. Freeze fracture electron microscopy was used to analyze the effects of fixative on the cell membrane. Confocal microscopic analysis was used to investigate three-dimensionally the effects of hypotonic treatment on the positions of chromosomes in fixed mitotic lymphocytes. Chromosome preparation-induced changes in the lengths of single chromosomes were also investigated. The results show that chromosome spreading involves significant water-induced swelling of mitotic cells during evaporation of the fixative from the slide, which is a prerequisite for chromosomal elongation, the production of metaphase spreads for chromosome analysis, and the appearance of Giemsa banding patterns. Hypotonic treatment is essential for well-spread metaphase chromosomes because it moves the chromosomes from a central to a more peripheral position in the cell, where they can be stretched more effectively during mitotic swelling. Like mitotic cells, isolated single chromosomes also have their own potential to swell and lengthen during chromosome preparation. We hypothesize that chromosome preparation leads to a genome-wide chromosomal region–specific opening of chromatin structures as GTG-light bands and sub-bands. Living cells may possess a similar mechanism, which is used only to open single chromatin structures to facilitate transcription. We propose the concept of chromosomal region–specific protein swelling.

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In contrast to those of metaphase chromosomes, the shape, length, and architecture of human interphase chromosomes are not well understood. This is mainly due to technical problems in the visualization of interphase chromosomes in total and of their substructures. We analyzed the structure of chromosomes in interphase nuclei through use of high-resolution multicolor banding (MCB), which paints the total shape of chromosomes and creates a DNA-mediated, chromosome-region-specific, pseudocolored banding pattern at high resolution. A microdissection-derived human chromosome 5-specific MCB probe mixture was hybridized to human lymphocyte interphase nuclei harvested for routine chromosome analysis, as well as to interphase nuclei from HeLa cells arrested at different phases of the cell cycle. The length of the axis of interphase chromosome 5 was determined, and the shape and MCB pattern were compared with those of metaphase chromosomes. We show that, in lymphocytes, the length of the axis of interphase chromosome 5 is comparable to that of a metaphase chromosome at 600-band resolution. Consequently, the concept of chromosome condensation during mitosis has to be reassessed. In addition, chromosome 5 in interphase is not as straight as metaphase chromosomes, being bent and/or folded. The shape and banding pattern of interphase chromosome 5 of lymphocytes and HeLa cells are similar to those of the corresponding metaphase chromosomes at all stages of the cell cycle. The MCB pattern also allows the detection and characterization of chromosome aberrations. This may be of fundamental importance in establishing chromosome analyses in nondividing cells.

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