Droplet on Demand Generation and Pairwise Merging

This application note demonstrates the ability of the Mitos Dropix® Droplet Merging System to reproducibly generate and subsequently merge droplets from tens to hundreds of nanolitres with a wide range of volume ratios. The amount of one component of a mixture relative to that of all other components Vr/(Vr+Vb) V + = b Vr Vr+Vb , is controlled by generating a pre-merger droplet sequence of suitably selected volumes. The novelty lies in the ability to generate and merge droplet pairs of typically tens of nanoliters in volume. There exists no such comparable commercially available automated continuous flow fluid handling systems. In tests, we show:

• Merging phase diagram – Droplet merging is parametrically investigated to establish effects of flow rate, and droplet volumes on the success of merging. Higher flow rates (10 – 20μL/min) mean a narrower size range of merged droplets (50 – 125 nL), and vice versa (40 – 200 nL for 5 – 10μL/min).
• Production of a concentration gradient – A sequence of 100 droplet pairs is generated, where the volume ratio of Vr/(Vr+Vb) is 25% at the front of the sequence, and 75% at the rear of the sequence. The total volume of Vr+Vb is held constant at 200nL. Merging pairwise leads to a sequence of 100 individual droplets displaying a continuous color transition from blue to red.