A. M. van den Berg

Micromachining of buried micro channels in silicon

A new method for the fabrication of micro structures for fluidic applications, such as channels, cavities, and connector holes in the bulk of silicon wafers, called buried channel technology (BCT), is presented in this paper. The micro structures are constructed by trench etching, coating of the sidewalls of the trench, removal of the coating at the bottom of the trench, and etching into the bulk of the silicon substrate. The structures can be sealed by deposition of a suitable layer that closes the trench. BCT is a process that can be used to fabricate complete micro channels in a single wafer with only one lithographic mask and processing on one side of the wafer, without the need for assembly and bonding. The process leaves a substrate surface with little topography, which easily allows further processing, such as the integration of electronic circuits or solid-state sensors. The essential features of the technology, as well as design rules and feasible process schemes, will be demonstrated on examples from the field of /spl mu/-fluidics.

Comprehensive analysis of miRNA expression in T-cell subsets of rheumatoid arthritis patients reveals defined signatures of naive and memory Tregs

Disturbed expression of microRNAs (miRNAs) in regulatory T cells (Tregs) leads to development of autoimmunity in experimental mouse models. However, the miRNA expression signature characterizing Tregs of autoimmune diseases, such as rheumatoid arthritis (RA) has not been determined yet. In this study, we have used a microarray approach to comprehensively analyze miRNA expression signatures of both naive Tregs (CD4+CD45RO-CD25++) and memory Tregs (CD4+CD45RO+CD25+++), as well as conventional naive (CD4+CD45RO−CD25−) and memory (CD4+CD45RO+CD25−) T cells (Tconvs) derived from peripheral blood of RA patients and matched healthy controls. Differential expression of selected miRNAs was validated by TaqMan-based quantitative reverse transcription-PCR. We found a positive correlation between increased expression of miR-451 in T cells of RA patients and disease activity score (DAS28), erythrocyte sedimentation rate levels and serum levels of interleukin-6. Moreover, we found characteristic, disease- and treatment-independent, global miRNA expression signatures defining naive Tregs, memory Tregs, naive Tconvs and memory Tconvs. The analysis allowed us to define miRNAs characteristic for a general naive phenotype (for example, miR-92a) and a general memory phenotype (for example, miR-21, miR-155). Importantly, the analysis allowed us to define miRNAs that are specifically expressed in both naive and memory Tregs, defining as such miRNA signature characterizing the Treg phenotype (that is, miR-146a, miR-3162, miR-1202, miR-1246 and miR-4281).

Etching methodologies in -oriented silicon wafers

New methodologies in anisotropic wet-chemical etching of -oriented silicon, allowing useful process designs combined with smart mask-to-crystal-orientation-alignment are presented in this paper. The described methods yield smooth surfaces as well as high-quality plan-parallel beams and membranes. With a combination of pre-etching and wall passivation, structures can be etched at different depths in a wafer. Designs, using the -crystal orientation, supplemented with pictures of fabricated devices, demonstrate the potential of using -oriented wafers in microsystem design.

EVOLUTION OF MAMMALIAN PANCREATIC RIBONUCLEASES

Pancreatic ribonucleases form a group of homologous proteins found in considerable quantities in the pancreas of a number of mammalian taxa and a few reptiles (Barnard, 1969; Beintema et al.,1973). The ribonuclease activity varies greatly in different species. Large quantities are found in ruminants and species that have a ruminant-like digestion, and in a number of species with cecal digestion (Fig. 1). Barnard (1969) proposed that an elevated level of pancreatic ribonuclease is the response to the necessity of digesting large amounts of ribonucleic acid derived from the microflora of the stomach of ruminants. This explanation agrees with the observation of Dobson and Wilson (1980) that the level of stomach lysozyme is also elevated in several ruminants and species that have a ruminant-like digestion.

Micro- and Nanofluidic Devices for Environmental and Biomedical Applications

During the last decade, an increasing amount of pocket-size chemistry equipment based on the so-called “lab-on-a-chip” approach has become available. Besides the popular application in the analysis of biological macromolecules, such chips in combination with portable electronic equipment are applicable in, for example, “point-of-care” ion analysis of body fluids, forensics, identification of explosives, tracking of pollution in environmental or waste waters, monitoring nutrients in agricultural or horticultural water, controlling quality in food production or process control in chemical industry. This paper discusses the development of a number of demonstrator chips and microsystems with applications in some of these fields. In particular, an integrated microsystem for flow injection analysis of ammonia in surface waters, a hydrodynamic chromatography chip for the analysis of particles and polymer molecules and a chip for ion analysis in blood are discussed in detail. The last chip may also find applications in environmental analysis.

Silicon micromachined hollow microneedles for transdermal liquid transfer

This paper presents an improved design and fabrication process for hollow micro needles with the proper mechanical strength and sharpness to be applied for painless transdermal transfer of liquids. Tests have shown that liquids like blood are drawn into the needle by capillary forces, reducing the need for active pumping. The fabrication method allows different needle shapes like blades and pencils, is robust enough to be applied for larger scale production, and enables the development of a complete micro-TAS for e.g. blood analysis.

Non-constant evolution rates in amino acid sequences of guinea pig, chinchilla and coypu pancreatic ribonucleases.

THE primary structures of the pancreatic ribonucleases from cow1, rat2, pig3,4, horse5, red deer and roe deer6, sheep7, goat8 and giraffe9 have been determined. From an analysis of these data we concluded that mammalian pancreatic ribonucleases have evolved with a rather constant evolution rate of about 1% substitution every 3 Myr (ref. 6). The validity of this conclusion, however, and possible exceptions have to be tested on a larger number of primary structures of mammalian ribonucleases.

Measuring the (d,He-2) reaction with the focal-plane detection system of the BBS magnetic spectrometer at AGOR

At intermediate energies, the (d, He-2) charge-exchange reaction can be used to observe Gamow-Teller strength in the direction. He-2 denotes the two-proton system being in the singlet S-1(0) state. In the present experiment the two protons, which in the laboratory frame are emitted into the forward direction, have been momentum analyzed and detected in coincidence by the same spectrometer and detector. Protons from deuteron breakup processes can induce a large accidental coincidence background because of the much larger breakup cross-section as compared to the (d, He-2) cross-section. Nevertheless, background-free He-2 spectra with a resolution of 145 keV at an incident energy of 170 MeV are obtained, allowing the identification of many levels with high precision in the residual nuclei. The essential features of the detection system and the data-acquisition and analysis techniques which make our (d 2 He) experiments possible are described. Two nuclei, C-12 and Mg-24, have been used as a test case

Improved Conversion Rates in Drug Screening Applications Using Miniaturized Electrochemical Cells with Frit Channels

This paper reports a novel design of a miniaturized three-electrode electrochemical cell, the purpose of which is aimed at generating drug metabolites with a high conversion efficiency. The working electrode and the counter electrode are placed in two separate channels to isolate the reaction products generated at both electrodes. The novel design includes connecting channels between these two electrode channels to provide a uniform distribution of the current density over the entire working electrode. In addition, the effect of ohmic drop is decreased. Moreover, two flow resistors are included to ensure an equal flow of analyte through both electrode channels. Total conversion of fast reacting ions is achieved at flow rates up to at least 8 μL/min, while the internal chip volume is only 175 nL. Using this electrochemical chip, the metabolism of mitoxantrone is studied by microchip electrospray ionization-mass spectrometry. At an oxidation potential of 700 mV, all known metabolites from direct oxidation are observed. The electrochemical chip performs equally well, compared to a commercially available cell, but at a 30-fold lower flow of reagents.

Modular concept for fluid handling systems. A demonstrator micro analysis system

A modular planar concept for fluid handling microsystems is presented. The concept is based on a planar Mixed Circuit Board with electrical and fluidic interconnections acting as a substrate for sensor and actuator modules. Several modules realised within this concept are presented, and the design as well as modelling and simulation of the fluidic components and systems is discussed. Furthermore, the general application of this concept in micro analysis systems is considered. Finally, the modular concept is demonstrated by a micro chemical analysis system containing micro-pumps, flow sensors, an optical absorption cell and control electronics.