This master thesis describes the development and design of microfluidic devices which use sheath flows to align and focus sample flows within a micro channel. The measurement of diluted particles (e.g.
cells, molecules) in a MEMS device for analytical purposes for example in life science and biotechnology makes it necessary to deal with detailed problems in microfluidics. Especially when it comes to single particle detection or manipulation it is important to ensure that the particles are passing the transducer area only one by one. This requires sharp focusing techniques. One elegant solution is to use hydrodynamic focusing in combination with sheath flows. The contribution in this thesis deals with the design and simple realization of microfluidic devices for focusing and 3D-alignment of coaxial and non-coaxial micro scale sample flows. For the experimental verification confocal laser microscope measurements were used.