research activities in 2007 - CSEM

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Bonding of Glass or Silicon Chips with a Self-Sealing Photostructurable Elastomer J. Auerswald, F. Cardot, P. Niedermann, A. Ibzazene, M. Fretz, N. Schmid, H. F. Knapp When it comes to the integration of planar electrodes on glass, quartz, silicon or thermoplastic chips into microfluidic systems, standard bonding methods like diffusion bonding, anodic bonding, thermo-compression bonding etc. do not work. Surfaces carrying electrodes cannot be sealed with a stiff material. The challenge is even bigger when two glass chips with facing electrodes and microfluidic channels in between are required by the application, with an alignment precision down to a few micrometers. Photostructurable polysiloxane could be a solution. The use of photostructurable polysiloxane combines two advantages: Firstly, the good alignment precision of microfluidic channels made by photolithography. Secondly, the reliable permanent bond of silicones to glass, even if the glass chips carry electrodes. Photostructurable polysiloxane is a material known from ISFET and ChemFET sensor packaging. There, typical lateral structure dimensions are several millimeters, sometimes slightly below 1 mm, and are shaped as simple O-rings [1, 2] . However, the use of this material class for microfluidic systems with microfluidic channel networks containing junctions or intersections at channel widths well below 1 mm, and electrodes in the channels has not been demonstrated yet. One of the critical issues is the precise bonding of the cured material to the glass counter chip which also has electrodes on its surface. Figure 1: LEFT: Bonded glass chips with facing top and bottom planar electrodes, alignment marks and fluidic access holes. The microfluidic channels are photo-structured into the elastomeric intermediate layer. RIGHT: Bonded chip filled with a colored fluid. 25 μm high microfluidic channels with a width down to 200 μm (and less), with channel junctions, into photostructured polysiloxane on a glass substrate with planar electrodes were structured. It was further achieved to permanently bond the cured material to counter glass chips with planar electrodes. The whole microfluidic system was leak tight, even without an external clamp (Figure 1). The elastomer-based photolithography and the precise bonding process allow for alignment accuracies down to a few micrometers. This high precision combined with good sealing provides a viable alternative to the until now rather unsatisfying sealing results obtained with classic negative tone photoresists such as SU-8, BCB, or polyimide. A possible application is shown in Figure 2. First, microelectrodes are fabricated on a bottom glass wafer. Then, in a second mask process, the photostructurable polysiloxane is deposited and structured. Before dicing, the bottom wafer is protected by a removable resist layer. After removal of the protective resist and surface activation, the chips can be bonded to the diced chips of the top wafer. The top glass chips also have electrodes and pre-drilled fluidic access holes. The bond is permanent, due to the applied surface activation. Fluidic connectors can be glued or tape-bonded above the fluidic access holes. Figure 2: CAD explosion model (left) and global view of the bonded chip with facing planar top and bottom electrodes, and Luer connectors (right). The alignment precision depends on the used bonding machine and can be as good as 1-2 micrometers with a device bonder. The chips sealed well over the entire gage pressure range up to 28’000 Pa (4 psi), even after the 10th pressure cycle (Figure 3). This is more than enough for typical microfluidic applications. Figure 3: Example of a sealing test. The chips seal well at pump gage pressures of 30’000 Pa (4 psi), even after the 10 th pressure cycle. This is more than good enough for typical microfluidic applications. Potential applications include high-end niche markets for labon-chip systems designed for dielectrophoresis, dielectric spectroscopy, low voltage AC-EOF pumping and other microfluidic applications requiring photolithographic electrodes. This work was partly funded by the EU (project IST-FP6- 027540, IntegramPLUS). CSEM thanks them for their support. [1] P. Temple-Boyer, J. Launay, I. Humenyuk, T. Do Conto, A. Martinez, C. Beriet, A. Grisel, Microelectronics Reliability 44 (2004) 443-447. [2] P. Arquint, M. Koudelka-Hep, B.H. van der Schoot, P. van der Val, N. F. de Rooij, Clin. Chem. 40/9 (1994) 1805-1809. 95
Sensor and Connector Integration into Microfluidic Systems using Biocompatible Tape Gaskets J. Auerswald, H. Haquette • , H. Keppner • , J. Nestler •• , S. Bigot ••• , M.-C. Beckers ∗ , J. Gavillet ∗∗ , G. Delapierre ∗∗ , N. Schmid, S. Berchtold, E. Portuondo-Campa, S. Graf, H. F. Knapp The project goal is to develop a thermoplastic microfluidic cartridge with an integrated glass-based surface plasmon resonance (SPR) sensor for label-free protein detection. Laser-cut tapes were used for sensor and connector integration. First prototypes were fabricated and tested in a protein demonstration assay. The non-specific binding behavior of the tapes with respect to antigen, antibodies, proteins, DNA and RNA was investigated. Laser-cut tape gaskets allow the integration of glass or silicon based sensors into low cost thermoplastic microfluidic systems [1] . The advantages of this bonding approach are: • High degree of design flexibility (multi-channel layouts). • Good bonding to polar (glass, quartz, silicon, ceramics) and non-polar (thermoplastics) surfaces. • Presence of bio-molecules on the sensor surface is possible during the bonding process (no heat, UV or plasma required). Tape bonding also allows the integration of fluidic connectors on the chip and the sealing of channels with cover tape. Figure 1 shows an assembled prototype and laser-cut tapes. Figure 1: Left: Prototype with glass-based SPR sensor chip, injection molded thermoplastic COC microfluidic channels, and fluidic srew connectors. Right: Laser-cut tapes were used for sensor chip bonding (bottom tapes), channel sealing (top tapes), and connector bonding. The prototypes have successfully been tested in protein demonstration assays. In these assays, human pain markers were detected in specific binding assays on glass chips. The glass chips, already carrying the probe molecules, were tapebonded to thermoplastic COC injection molded microfluidic channels. Further, a gel actuator was successfully tested as an alternative to the external pump, used today. This gel actuator, together with sample, buffer and reference reservoirs, will be integrated into the cartridge in the future. Figure 2: PE-CVD coating of the channel substrates. All channels were coated hydrophilically, except at the junction area, where a hydrophobic flow stop was desired. The coated chip was sealed with an uncoated laser-cut cover tape. For controlled actuation and flow behavior with the integrated gel actuators, the cartridge will also possess hydrophobic flow stops at the inlet channel junction area. For this purpose, the COC cartridge will be treated with PE-CVD coatings to define hydrophilic and hydrophobic channel sections. The wetting 96 angle for aqueous solutions is defined by the prevailing polar or non-polar bond character in the coating. First tests demonstrated the feasibility of the flow stops (Figure 2). For sensitive protein assays, it is important that the proteins are delivered to the sensor and not lost due to non-specific binding at the microfluidic channel walls. The bonding tapes, the cover tapes, the COC and the PE-CVD coatings were tested for non-specific binding of antigens, proteins from serum, biopsy and cell lysate, and antibodies. In addition, the tapes were also tested for non-specific binding of DNA and RNA. Tapes, COC and PE-CVD coatings showed relatively low non-specific binding in these tests (Figure 3). Figure 3: Example of a non-specific binding test with antigen and proteins from serum, biopsy and cell lysate. Compared to reference glass and COC slides, the fluorescence signal indicates low nonspecific binding of bio-molecules on a number of tested tapes. The work was supported by the EU (IST-FP6-016768). SPR chips were provided by Zeptosens (a division of Bayer AG). • HE-ARC, La Chaux-de-Fonds, Switzerland •• Technische Universität Chemnitz, Germany ••• Cardiff University, UK ∗ Eurogentec SA, Belgium ∗∗ CEA Grenoble, France [1] J. Auerswald, et al., Bonding of SPR Sensors on Glass Chips to Thermoplastic Microfluidic Scaffolds, Proc. Smart Systems Integration Conference, Paris, March 27-28, 2007, 153-160.
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CONTENTS PREFACE 5 RESEARCH ACTIVIT
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PREFACE Dear Reader, In this report
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TissueOptics - Portable SpO2 Monito
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Counterfeit - Machine Readable Cove
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ArrayFM - An Atomic Force Microscop
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Encoder - Nanometric Optical Absolu
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PackTime - Zero-Level Packaging of
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TissueOptics - Portable SpO2 Monito
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spectrometer applications so CSEM h
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As a first step, CSEM is building s
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Data Fusion for Wireless Distribute
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A High-Performance 2.4 GHz RF Front
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Quasi-Harmonic Quadrature CMOS Rela
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icycam, a System-On Chip (SoC) for
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PHOTONICS Nicolas Blanc The Photoni
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Optoelectronic Test Equipment for I
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Compact Illumination Modules Based
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Efficient Screening and Formulation
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Optical Fill Factor Enhancement for
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Page 49 and 50: Towards an Optical Switch with J-ag
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Page 57 and 58: Parallel Nanoscale Dispensing of Li
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