Edited by Vinothan N. Manoharan, Harvard University, Cambridge, MA, and accepted by Editorial Board Member John D. Weeks August 1, 2018 (received for review October 23, 2017)
Whereas crystals and other geometrical structures can be self-assembled under equilibrium conditions from a few particles with a few, often simple, identical interactions, functional materials require a multitude of specific interactions between many different types of particles and nonequilibrium, often hierarchical assembly. Here, we introduce a set of building blocks on the colloidal micrometer scale with designed valence and specificity that readily make linear, branched, or other programmed connected networks, yet maintain the flexibility needed to fold, unfold, or restructure from the original backbone. We demonstrate the self-assembly of alternating copolymers, hetero chains, trivalent clusters, and a dynamic programmability by opening and closing chain ends.
Nature self-assembles functional materials by programming flexible linear arrangements of molecules and then folding them to make 2D and 3D objects. To understand and emulate this process, we have made emulsion droplets with specific recognition and controlled valence. Uniquely monovalent droplets form dimers: divalent lead to polymer-like chains, trivalent allow for branching, and programmed mixtures of different valences enable a variety of designed architectures and the ability to subsequently close and open structures. Our functional building blocks are a hybrid of micrometer-scale emulsion droplets and nanoscale DNA origami technologies. Functional DNA origami rafts are first added to droplets and then herded into a patch using specifically designated “shepherding” rafts. Additional patches with the same or different specificities can be formed on the same droplet, programming multiflavored, multivalence droplets. The mobile patch can bind to a patch on another droplet containing complementary functional rafts, leading to primary structure formation. Further binding of nonneighbor droplets can produce secondary structures, a third step in hierarchical self-assembly. The use of mobile patches rather than uniform DNA coverage has the advantage of valence control at the expense of slow kinetics. Droplets with controlled flavors and valences enable a host of different material and device architectures.
↵1Y.Z. and X.H. contributed equally to this work.
Author contributions: Y.Z., X.H., J.B., N.C.S., and P.M.C. designed research; Y.Z., X.H., and R.Z. performed research; Y.Z., X.H., R.Z., and R.S. contributed new reagents/analytic tools; Y.Z., X.H., R.Z., R.S., and J.B. analyzed data; and Y.Z., X.H., J.B., N.C.S., and P.M.C. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. V.N.M. is a guest editor invited by the Editorial Board.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1718511115/-/DCSupplemental.
Published under the PNAS license.
