Right from its entrance, Disneyland is designed to cast an illusion upon its visitors. The first area – Main Street – seems to stretch for miles towards the towering castle in the distance. All of this relies on visual trickery. The castle’s upper bricks and the upper levels of Main Street’s buildings are much smaller than their ground-level counterparts, making everything seem taller. The buildings are also angled towards the castle, which makes Main Street seem longer, building the anticipation of guests.
These techniques are examples of forced perspective, a trick of the eye that makes objects seem bigger or smaller, further or closer than they actually are. These illusions were used by classical architects to make their buildings seem grander, by filmmakers to make humans look like hobbits, and by photographers to create amusing shots. But humans aren’t the only animals to use forced perspective. In the forests of Australia, the male great bowerbird uses the same illusions to woo his mate.
DNA is most famous as a store of genetic information, but Shawn Douglas from the Dana-Farber Cancer has found a way to turn this all-important molecule into the equivalent of sculptor’s clay. Using a set of specially constructed DNA strands, his team has fashioned a series of miniscule sculptures, each just 20-40 nanometres in size. He has even sculpted works that assemble from smaller pieces, including a stunning icosahedron – a 20-sided three-dimensional cage, built from three merged parts.
Douglas’s method has more in common with block-sculpting that a mere metaphor. Sculptors will often start with a single, crystalline block that they hack away to reveal the shape of an underlying figure. Douglas does the same, at least on a computer. His starting block is a series of parallel tubes, each one representing a single DNA helix, arranged in a honeycomb lattice. By using a programme to remove sections of the block, he arrives at his design of choice.
With the basic structure set down, Douglas begins shaping his molecular clay. He builds a scaffold out of a single, long strand of DNA. For historical purposes, he uses the genome of the M13 virus. This scaffold strand is ‘threaded’ through all the tubes in the design with crossovers at specific points to give the structure some solidity. The twists and turns of the scaffold are then fixed in place by hundreds of shorter ‘staple’ strands, which hold the structure in place and prevent the scaffold from unfolding.
The sequences of both the scaffold and staple strands are tweaked so that the collection of DNA molecules will stick together in just the right way. Once all the strands are created, they’re baked together in one hotpot and slowly cooled over a week or so. During this time, the staples stick to predetermined parts of the scaffold and fold it into the right shape. The slow cooling process allows them to do this in the right way; faster drops in temperature produce more misshapen forms.
The result: a series of six structures that Douglas viewed under an electron microscope: a monolith, a square nut, a railed bridge, a slotted cross, a stacked cross and a genie bottle. These basic shapes illustrate the versatility of the nano-origami approach, and they can also be linked together to form larger structures. Using staples that bridge separate scaffolds, Douglas created a long chain of the stacked cross units. Most impressively of all, he made an icosahedron by fusing three distinct subunits.