 Lipid nanoparticles, LNP, are the leading systems for in vivo delivery of small interfering RNA, CERNA, for therapeutic applications. Formulation of LNP-CERNA systems requires rapid mixing of solutions containing cationic lipid with solutions containing CERNA. We show that microfluidic mixing techniques, which permit millisecond mixing at the nanoliter scale, can reproducibly generate limit-size LNP-CERNA systems 20 nanometers and larger. This article was authored by Nathan Embelevo, Jens Hoft, Paolo J. C. Lin and others.