Methods for preparing polynucleotide transfection complexes

Methods are provided for the preparation of transfection complexes of polynucleotides and polycations, especially cationic lipids, suitable for delivering polynucleotides to cells. In particular, methods are provided for preparing transfection complexes using a reduced-volume, dual-feed process. Complexes are formed upon the collision of two feed stream, containing polynucleotides and polycation, respectively, under conditions resulting in turbulent mixing conditions in minimal volume, and removal of transfection complexes under laminar flow conditions. Alternatively, the components are mixed in a static mixer. The process is easily scaleable and highly reproducible.