A microfluidic device that comprises several microchannel structures in which there are an inlet port, an outlet port and there between a structural unit comprising a fluidic function. The structural unit can be selected amongst units enabling a) retaining of nl-aliquots comprising constituents which has been defined by mixing of aliquots within the microfluidic device (unit A), b) mixing of aliquots of liquids (unit B), c) partition of larger aliquots of liquids into smaller aliquots of liquids and distributing the latter individually and in parallel to different microchannel structure of the same microfluidic device (unit C), d) quick penetration into a microchannel structure of an aliquot of a liquid dispensed to an inlet port of a microchannel structure (unit D), and e) volume definition integrated within a microchannel structure (unit E).