By Ed Yong | November 29, 2012 1:17 pm

For tens of thousands of years, humans have created sculptures by carving pieces from a solid block. They have chipped away at stone, metal, wood and ceramics, creating art by subtracting material. Now, a group of scientists from Harvard University have figured out how to do the same thing with DNA.

First, Yonggang Ke builds a solid block of DNA from individual Lego-like bricks. Each one is a single strand of the famous double helix that folds into a U-shape, designed to interlock with four neighbours. You can see what happens in the diagram below, which visualises the strands as two-hole Lego bricks. Together, hundreds of them can anneal into a solid block. And because each brick has a unique sequences, it only sticks to certain neighbours, and occupies a set position in the block.

This means that Ke can create different shapes by leaving out specific bricks from the full set, like a sculptor removing bits of stone from a block. Starting with a thousand-brick block, he carved out 102 different shapes, with complex features like cavities, tunnels, and embossed symbols. Each one is just 25 nanometres wide in any direction, roughly the size of the smallest viruses.

Kes work, led by Harvards Peng Yin, is the latest achievement from the growing field of DNA origami. Its forefather was the chemist Ned Seeman, who created a DNA cube in 1991 by annealing separate strands together. He followed this with a simple tubes and lattices, but his technique was laborious and inefficient.

Paul Rothemund greatly improved it in 2006. He showed that you can fold a long 7,000-letter strand of viral DNA into a specific shape by using hundreds of shorter snippets. These match different part of the viruss genome and staple it into place. Mix the strands togetherthe long scaffold and short staplesand they spontaneously fold into the right shape. Rothemund and others used the origami technique to create miniature maps, smiley faces, the word NED (in honour of Seeman), and more elaborate shapes like boxes.

Last year, Yins team broke off from the scaffold-and-staples tradition. I wrote about their work for Nature News:

Bryan Wei and his colleagues make shapes out of single strands of DNA just 42 letters long. Each strand is unique, and folds to form a rectangular tile. When mixed, neighbouring tiles stick to each other in a brick-wall pattern, and shorter boundary tiles lock the edges in place.

In their simplest configuration, the tiles produce a solid 64-by-103-nanometre rectangle, but Wei and his team can create more complex shapes by leaving out specific tiles. Using this strategy, they created 107 two-dimensional shapes, including letters, numbers, Chinese characters, geometric shapes and symbols. They also produced tubes and rectangles of different sizes, including one consisting of more than 1,000 tiles.

The team designed a robot to pick the tiles. The desired shape is drawn using a graphical interface, and the robot picks out and mixes the required strands. It can produce 48 shapes in as many hours. Millions of shapes can be crafted from the same set of tiles simply by leaving some out. Once you have a pre-synthesized library, you dont need any new DNA designs, says Yin. You just pick your molecules.

Excerpt from:
DNA Lego bricks produce nano-sculptures