During the last decade, world-wide developments in micro-fabrication technologies have led to numerous Lab-On-a-Chip (LOC) micro-systems covering a wide spectrum of biotechnological applications. Although early LOC developments were driven by glass and silicon micro-fabrication techniques, in recent years polymeric-based LOC have been intensively developed. Taking advantage of each material, a hybrid device associating an active silicon chip with a passive polymeric micro-part has been developed to produce an addressable Cell-chip for individual cell manipulation and sorting. The complete hybrid micro-fluidic device fabrication is described here, including polymer structuring, hermetical sealing, biocompatibility studies, and fluidic interconnections with the sample as well as detection aspects. The cell manipulation is based on dielectrophoresis, which allows cell motion without fluid flow. First biological results will be presented.
The lab-on-a-chip approach has been increasingly present in biological research over the last ten years, high-throughput analyses being one of the promising utilization.
The work presented here has consisted in developing an automated genotyping system based on a continuous flow analysis which integrates all the steps of the genotyping process (PCR, purification and sequencing).
The genotyping device consists of a disposable hybrid silicon-plastic microfluidic chip, equipped with a permanent external, heating/cooling system, syringe-pumps based injection systems and on-line fluorescence detection. High throughput is obtained by performing the reaction in a continuous flow (1 reaction every 6min per channel) and in parallel (48 channels).
We are presenting here the technical solutions developed to fabricate the hybrid silicon-plastic microfluidic device. It includes a polycarbonate substrate having 48 parallel grooves sealed by film lamination techniques to create the channels. Two different solutions for the sealing of the channels are compared in relation to their biocompatibility, fluidic behavior and fabrication process yield. Surface roughness of the surface of the channels is the key point of this step. Silicon fluidic chips are used for thermo-cycled reactions. A specific bonding technique has been developed to bond silicon chips onto the plastic part which ensures alignment and hermetic fluidic connexion. Surface coatings are studied to enhance the PCR biocompatibility and fluidic behavior of the two-phase liquid flow. We then demonstrate continuous operation over more than 20 hours of the component and validate PCR protocol on microliter samples in a continuous flow reaction.
SU-8, negative-tone epoxy base, photoresist has a great potential for ultra-thick high aspect ratio structures in low cost micro-fabrication technologies. Commercial formulation of NanoTM SU-8 2075 is investigate, process limitations are discuss. Good layer uniformity (few %) for single layer up to 200 μm could be obtained in a covered RC8 (Suss-MicroTec) spin coater, but for ultra-thick microstructures it is also possible to cast on the wafer a volume controlled of resist up to 1.5 mm without barrier. Long baking times are necessary for a well process control. The layout of the photo-masks design and process parameters have great impact on residual stress effects and adhesion failures, especially for dense SU-8 patterns on metallic under layer deposited on silicon wafers. A specific treatment applied before the resist coating definitely solved this problem.
Bio-fluidic applications of on-wafer direct prototyping (silicon, glass, plastics) are presented. An example will be given on prototyping dielectophorectic micro-cell manipulation component. The SU-8 fluidic structure is made by a self planarized multi-level process (application for 2,5 to 3D microstructures). Biotechnology applications of integrated micro-cells could be considered thanks to the SU-8 good resistance to PCR (Polymerase Chain Reaction).
Future developments are focusing on the SU-8 capabilities for Deep Reactive Ion Etching of plastic and 3D shaping of microstructures using a process called : Multidirectional Inclined Exposure Lithography (MIEL).
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