Microfabrication and application of reservoir pins for liquid transfer in biotechnology

Microarraying involves laying down genetic elements onto a solid substrate for DNA analysis on a massively parallel scale. Microarrays are prepared using a pin-based robotic platform to transfer liquid samples from microtitre plates to an array pattern of dots of different liquids on the surface of glass slides where they dry to form spots diameter < 200 μm. This paper presents the design, materials selection, micromachining technology and performance of reservoir pins for microarraying. A conical pin is produced by (i) conventional machining of stainless steel or wet etching of tungsten wire, followed by (ii) micromachining with a focused laser to produce a microreservoir and a capillary channel structure leading from the tip. The pin has a flat end diameter < 100 μm from which a 500 μm long capillary channel < 15 μm wide leads up the pin to a reservoir. Scanning electron micrographs of the metal surface show roughness on the scale of 10 μm, but the pins nevertheless give consistent and reproducible spotting performance. The pin capacity is 80 nanolitres of fluid containing DNA, and at least 50 spots can be printed before replenishing the reservoir. A typical robot holds can hold up to 64 pins. This paper discusses the fabrication technology, the performance and spotting uniformity for reservoir pins, the possible limits to miniaturization of pins using this approach, and the future prospects for contact and non-contact arraying technology.

Multi-colour switching of polymer stabilized chiral nematic liquid crystal devices

We have fabricated a series of polymer stabilized chiral nematic test cells for use as flexoelectro-optic devices. The devices fabricated were based on commercial chiral nematic mixtures which were polymer stabilized so as to enhance the uniformity and stability of the uniform lying helix texture in the cells. During fabrication and test procedures a series of unusual scattering states have been observed within the devices at different viewing angles. The observations made so far indicate that the properties of the scattering state lies somewhere between the focal conic texture and the Grandjean or planar texture and that the devices exhibit both a helical pitch selective reflection and scattering effect. What is even more dramatic is that the wavelength selectivity of the scattering effect can be tuned by an applied field. In addition, we show that it is possible to achieve good uniform lying helix textures from such devices. Moreover, we show that in certain cases the spontaneous alignment of the helix in the plane of the device opens up the possibility of a new mode of switching. Flexoelectric, Redshift, Coloured scattering, Liquid crystal, Polymer-stabilized liquid-crystal;.

Pattern formation and spatial solitons in bistable liquid-crystal microcavities

We report on spatial pattern formation, and appearances of 'optical bullet holes' in single-mode microcavities that are filled with liquid-crystals, when pumped above the cavity resonance frequency. These phenomena only occur beyond the bistability threshold. ©2002 Optical Society of America.

Dynamics Of Fine Particles In Liquid-Solid Fluidized Beds

On the basis of the Local Equilibrium Model (LEM), fine particles with large Richardson-Zaki exponent n show, under certain conditions during bed expansion and collapse, different dynamic behavior from particles with small n. For an expansion process there may be a concentration discontinuity propagating upward from the distributor, and, on the contrary, for a collapse process there may be a progressively broadening and upward-propagating continuous transition zone instead of discontinuity. The predictions of the bed height variation and the discontinuity trace have been validated experimentally. (c) 2007 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.