Complex shapes self-assembled from single-stranded DNA tiles

Complex, self-assembling, two-dimensional nanostructures can be built of single-stranded DNA tiles by a method that allows individual control of more than one thousand distinct components. Design and self-assembly of DNA mosaics Programmed DNA self-assembly is widely used to create nanometre-sized structures. Modular strategies promise simplicity and versatility, yet cannot easily assemble large numbers of small strands into prescribed and complex shapes. Peng Yin and colleagues overcome this problem by designing a molecular canvas: a rectangle assembled from single-stranded tiles each consisting of a short and unique 42-base DNA strand that folds into a 3-nanometre-by-7-nanometre tile and attaches to 4 neighbouring tiles. A desired shape, drawn on the canvas, is produced by simply mixing those strands that correspond to pixels covered by the target shape, and excluding 'off'-pixel strands. With a master strand collection for a 310-pixel canvas, the team then creates more than 100 distinct and complex two-dimensional shapes that establish the method as a simple, modular and robust framework for assembling short synthetic DNA strands into complex DNA nanostructures. Programmed self-assembly of strands of nucleic acid has proved highly effective for creating a wide range of structures with desired shapes 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 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 , 15 , 16 , 18 , 19 , 20 , 21 , 25 . Modular strategies are in principle simpler and more versatile and have been used to assemble DNA 2 , 3 , 4 , 5 , 8 , 10 , 11 , 12 , 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 assemb