Microdroplet-based synthesis and centrifuge-free retrieval of nanoparticles via a continuous flow micropost array railing system

Microfluidic droplet-based microreactors offer significant advantages for the synthesis of nanoparticles, including high control of reagent loading and mixing. One limitation, however, is that retrieving synthesized nanoparticles from microdroplets typically requires laborious and time-consuming “off-chip” procedures (e.g., droplet collection, centrifugication and nanoparticle resuspension). To bypass these issues, here we introduce a continuous flow microfluidic system to enable the rapid and autonomous droplet-based generation and retrieval of nanoparticles. Specifically, we utilize a micropost array railing technique in order to passively: (i) generate microdroplets in which nanoparticles are synthesized, (ii) guide the particle-containing droplets into an oil-phase wash solution (i.e., to remove surfactant), and (iii) “lyse” the microdroplets to release the nanoparticles into the water flow. Experimental results demonstrated the successful synthesis and retrieval of magnetic iron-oxide nanoparticles, which can be employed for applications including bioseparation, biotagging and imaging.