Faithful chromosome segregation in mitosis requires the formation of a bipolar mitotic spindle with stably attached chromosomes. Once all of the chromosomes are aligned, the connection between the sister chromatids is severed by the cysteine protease separase. Separase also promotes centriole disengagement at the end of mitosis. Temporal coordination of these two activities with the rest of the cell cycle is required for the successful completion of mitosis. In this study, we report that depletion of the microtubule and kinetochore protein astrin results in checkpoint-arrested cells with multipolar spindles and separated sister chromatids, which is consistent with untimely separase activation. Supporting this idea, astrin-depleted cells contain active separase, and separase depletion suppresses the premature sister chromatid separation and centriole disengagement in these cells. We suggest that astrin contributes to the regulatory network that controls separase activity.

Macroporous silicon membranes form the basis for different types of applications including photonic crystals, [1][2][3][4][5][6] Brownian ratchets, [7] omnidirectional short-pass filters, [8][9][10][11] templates for nanowire formation, [12] microchannel plates, [13,14] and supports for microarrays. [15,16] Due to the intrinsically large and fluidically accessible surface, devising a microarray support derived from macroporous silicon promises a dramatic gain in analytical performance over existing concepts. The optical properties of the narrow pores in the UV, visible, and near-IR (200 nm< k < 700 nm), however, render macroporous silicon incompatible with all types of fluorescence assays. Strong propagation losses of light in the narrow pores and fluorescence interference effects near the reflecting silicon impair the fluorescence yield. [9,17,18] Here, we present a new class of highly transparent macroporous membranes, fabricated by partial oxidation of an ordered macroporous silicon membrane. The oxidation yields a macroporous SiO 2 membrane with a grid of silicon walls that divides the membrane into optically isolated domains of macroporous SiO 2 . The silicon grid suppresses lateral spreading of light in the structure. In the membrane, the densely folded surface ensures an efficient interaction of light falling through the membrane with molecules captured on the surface of the pore walls. A DNA-hybridization experiment demonstrates the use of the three-dimensional photonic structure as a microarray support. Figure 1 shows a schematic drawing of the partially oxidized macroporous silicon membrane. The membrane is compartmentalized into SiO 2 domains that are optically isolated by a grid of pore walls with a residual core of silicon; each compartment comprises an array of pores. Figure 2a shows an optical microscopy image of the membrane under back-side illumination. The bright grid corresponds to the SiO 2 walls that act as optical waveguides (refractive index, n(SiO 2 ) = 1.46). The compartment walls with the residual core of silicon and the pores appear dark.The fabrication strategy of the partially oxidized macroporous silicon membrane relies on the difference in oxidation time required to completely convert silicon pore walls with different thicknesses into SiO 2 . The strategy has two components: First, the fabrication of a macroporous silicon membrane with a periodic pore pattern that contains pore walls with two different thicknesses: one with regular thickness and one with increased thickness. Second, the thermal oxidation of the membrane to convert the pore walls with regular thickness into SiO 2 , while the pore walls with increased thickness keep a residual core of silicon.The fabrication of the macroporous silicon membrane starts with the photolithographic definition of the pore pattern. Compartment walls with increased thickness are defined by periodically skipping or shifting columns and rows in a regular square lattice of pores to locally increase the center-to-center distance of the pores. The...

Partial oxidation of macroporous silicon membranes with different pore wall thicknesses results in a regular compartmentalized structure of SiO2 domains separated by opaque silicon, as shown on the cover. Dertinger and co‐workers report on p. 3135 that control of the experimental conditions ensures the flatness of the partially oxidized macroporous silicon. Fluorescence crossover is minimized within the photonic crystal, enabling its use as a microarray support for sensitive bioanalytic applications, such as DNA hybridization.

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PACS 43.20.Mv, 81.05.Gc In this paper we present a three-dimensional waveguide structure with unique optical and fluidic properties and demonstrate its application as a substrate for DNA microarrays. The structure is fabricated by thermal oxidation of a macroporous silicon membrane with a periodic pattern of discrete microchannels running perpendicular through the substrate. Partial oxidation generates compartments with channel walls that are completely converted into SiO 2 but leaves a rectangular grid of silicon walls separating the SiO 2 compartments. We demonstrate that the SiO 2 walls act as optical waveguides and the opaque silicon walls divide the substrate into optically isolated compartments. In DNA microarray experiments, we show that the silicon walls of the compartments prevent cross talk between adjacent DNA spots. The structure is compatible with all conventional read-out techniques such as fluorescence, chemiluminescence, and precipitation staining.