Fig. 1.

A schematic of sequential self-assembly. a Step 1: two droplets, B and C, with partially hybridized pairs of DNA strands are inert. Step 2: a droplet with an initiator strand, A, is introduced. Step 3: the initiator strand fully hybridizes to the protection strand on B through toehold strand displacement and frees the protected strand, leading to the activation of droplet B. The freed strand on B can then hybridize with the protection strand on C making a B–C bond and activating C for further binding. b Schematic of the toehold displacement reaction showing details corresponding to the activation process of (a)