Each layer can carry therapeutics as well as molecules that help the particles find and enter cancer cells. In the new work, the researchers used a microfluidic mixing device that allows them to sequentially add layers as the particles flow through a microchannel. This microfluidic device can be used to assemble the drug delivery nanoparticles rapidly and in large quantities. They say this means it would be realistic to produce more than enough for clinical trials and patient use. To demonstrate the technique, the researchers created layered nanoparticles loaded with the immune molecule ­interleukin-­12; they have previously shown that such particles can slow growth of ovarian tumors in mice.