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 a glass slide after activation of the surfaces, for which A ZEPTO plasma oven from Diener Electronic was used. Details on the fabrication process can be found in Supplementary Information, S2.