Complex shapes self-assembled from single-stranded DNA tiles

Programmed self-assembly of strands of nucleic acid has proved highly effective for creating a wide range of structures with desired shapes(1-25). A particularly successful implementation is DNA origami, in which a long scaffold strand is folded by hundreds of short auxiliary strands into a complex shape(9,14-16,18-21,25). Modular strategies are in principle simpler and more versatile and have been used to assemble DNA(2-5,8,10-13,17,23) or RNA(7,22) tiles into periodic(3,4,7,22) and algorithmic(5) two-dimensional lattices, extended ribbons(10,12) and tubes(4,12,13), three-dimensional crystals(17), polyhedra(11) and simple finite two-dimensional shapes(7,8). But creating finite yet complex shapes from a large number of uniquely addressable tiles remains challenging. Here we solve this problem with the simplest tile form, a 'single-stranded tile' (SST) that consists of a 42-base strand of DNA composed entirely of concatenated sticky ends and that binds to four local neighbours during self-assembly(12). Although ribbons and tubes with controlled circumferences(12) have been created using the SST approach, we extend it to assemble complex two-dimensional shapes and tubes from hundreds (in some cases more than one thousand) distinct tiles. Our main design feature is a self-assembled rectangle that serves as a molecular canvas, with each of its constituent SST strands-folded into a 3 nm-by-7 nm tile and attached to four neighbouring tiles-acting as a pixel. A desired shape, drawn on the canvas, is then produced by one-pot annealing of all those strands that correspond to pixels covered by the target shape; the remaining strands are excluded. We implement the strategy with a master strand collection that corresponds to a 310-pixel canvas, and then use appropriate strand subsets to construct 107 distinct and complex two-dimensional shapes, thereby establishing SST assembly as a simple, modular and robust framework for constructing nanostructures with prescribed shapes from short synthetic DNA strands.