The matured etching and lithographic techniques originally developed in the semiconductor industry to process silicon wafers with nanometer accuracy were a driving force for the development of the first microfluidic circuits. However the initial silicon chips were gradually replaced by polymeric devices, which can be mass produced by means of simple and cost-effective replication techniques such as injection molding or hot embossing. Nevertheless today silicon still remains the material of choice for certain applications because it has several unique properties: simple generation of an inert surface (SiO2 ) by oxidation, high-temperature stability, high chemical resistance to organic solvents and acids, well-established bonding and coating processes, an extensive knowledge about coatings, and its well-defined and excellent mechanical properties as a single crystal material. Channel walls are usually very smooth, complex structures can be fabricated, and electric functions such as heaters and sensors can be integrated when required as part of the microfluidic component.
A key detection technique in conventional biochemical analysis techniques such as electrophoresis and liquid chromatography is UV/VIS absorbance detection and hence there is a need to microminiaturize and to implement this technique in silicon microfluidics. We have developed a novel cost-effective approach for UV/VIS absorbance measurements in silicon microfluidic channels, implementing a micro-optical light coupler on top of the silicon wafer to couple light in and out the fluidic channel , instead of propagating a UV or visible light beam in the plane of the silicon wafer by using embedded optical fibers or waveguides. Decoupling the optics from the microfluidics opens opportunities in terms of low cost mass production of the optics and the development of generic detection systems for parallel measurements on different types of microfluidic circuits. The detection system was designed using optical ray tracing simulations, prototyped in PMMA by means of Deep Proton Writing and applied on a U-shaped microfluidic test-channel. This channel was fabricated in silicon by means of wet etching at the FEMTO-ST research institute in France (Prof. C. Gorecki) as part of a project within the European Network of Excellence on Micro-Optics (NEMO, 6th FP). With this detection system the absorbance of coumarin dye samples with molar concentrations from 0.6µM to 6mM can be characterized.
|Sara Van Overmeire|
|+32 2 629 36 58|
|+32 2 629 34 51|
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