An overview is given of current developments in micromixing technology, where the emphasis is on liquid mixing in passive micromixers. The mixers presented are differentiated by the hydrodynamic principle employed, and four important principles are discussed in some detail: hydrodynamic focusing, flow separation, chaotic advection, and split-and-recombine flows. It is shown that these principles offer excellent mixing performance in various dynamical regimes. Hydrodynamic focusing is a concept working very much independently of the Reynolds number of the flow. Flow separation offers rich dynamical behavior over a Reynolds number scale of several hundred, with superior performance compared to purely diffusive mixing already found at low Reynolds numbers. For chaotic advection, different implementations tailor-made for low and comparatively high Reynolds numbers exist, both leading to an exponential increase of the interface between two fluids. Split-and-recombine flows can only be realized in a close-to-ideal form in the low Reynolds number regime. Corresponding mixers can be equipped with comparatively wide channels, enabling a favorable ratio of throughput to pressure drop. The overview given in this article should enable a potential user of micromixing technology to select the most favorable concept for the application envisaged, especially in the field of chemical process technology
A general multipurpose microchip technology platform for point-of-care diagnostics has been developed. Real-time nucleic acid sequence-based amplification (NASBA) for detection of artificial human papilloma virus (HPV) 16 sequences and SiHa cell line samples was successfully performed in cyclic olefin copolymer (COC) microchips, incorporating supply channels and parallel reaction channels. Samples were distributed into 10 parallel reaction channels, and signals were simultaneously detected in 80 nl volumes. With a custom-made optical detection unit, the system reached a sensitivity limit of 10(-6) microM for artificial HPV 16 sequences, and 20 cells microl(-1) for the SiHa cell line. This is comparable to the detection limit of conventional readers, and clinical testing of biological samples in polymer microchips using NASBA is therefore possible.
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