Fabrication of microfluidic channels. The upper layer of the microfluidic channels was fabricated using a two-step process: The devices were designed in Solidworks® and printed (Stratasys Objet Pro 30 3D-Printer) to yield a mal. A mixture of curing agent with silicone elastomer base (1:10 m/m, degassed in vacuo) was poured into the mal, and was allowed to polymerize in an oven at 75 °C for 30 minutes. PDMS was bonded with glass slide a�er ac�va�on of the surfaces, for which A ZEPTO plasma oven from Diener Electronic was used. Details on the fabrica�on process can be found in Supplementary Informa�on, S2. Note: This sec�on includes valida�ons that the devices (with internal volumes ranging from 9-30 mL) can provide adequate mixing at flow rates between at least 3-10 µL min -1 . We chose to use a device with a 9 µL channel because this device provided the highest surfaceto-volume ra�o among the available set.