When you read the word “DNA”, a clear image pops into your head: you probably picture the iconic double helix, a long, twisted molecular ladder whose steps spell out the hidden language at the core of life. There is something almost metaphysical about our cultural vision of the molecule, making it seem somehow both physical and abstract, material and disembodied. Mostly, we think of DNA as an instruction manual that controls the construction of biological bodies; we are not used to thinking of it as a material we can build things out of.
These smiley faces are made entirely of DNA and measure only about 100 nm across. When I first saw them, I was surprised—not just because they are incredibly small, much smaller than your own cells, yet almost perfectly regular in shape and size—but also because it was the first time I saw DNA as something other than the molecular incarnation of a linear string of code.
These structures are known as “DNA origami”, and, much like paper origami, they are created by folding DNA strands onto themselves according to specific patterns. This photograph marks the inception of a completely new field of molecular nanotechnology that exploits the molecular structure of DNA to generate complex morphologies. The scientist who pioneered DNA origami in 2006, Paul Rothemund from Caltech, has paved the way for the production of a variety of shapes, including three-dimensional ones. Unlike paper origami, however, human hands are not involved in the folding process; no hand could be small enough for that task. The shapes you see are self-organized, spontaneously assembling into precise structures.
DNA is highly information-dense, meaning it is capable of encoding a vast amount of information within a minuscule volume of matter. It achieves this through a sequence of molecular units called “bases”. Each base can selectively bind to a complementary base with remarkable specificity, resulting in highly predictable and programmable interactions with other DNA strands.
To create a DNA origami, the first requirement is a long, single strand of DNA — and that’s not something you can easily prepare from scratch in a test tube. While DNA is typically found in its customary double-helix form, single-stranded DNA also exists in nature, if you know where to look. The strands of DNA used for the origami — 6407 nucleotides long — are extracted from a virus called the M13 bacteriophage. (Incidentally, I’m always surprised to discover how our most advanced technologies are predominantly non-human, resembling a witches' brew or a Frankensteinian assemblage of components scavenged here and there from wildly different organisms). Shorter DNA sequences were then synthesized in the lab to selectively bind to specific parts of the long strand. These shorter sequences served as 'molecular staples,' facilitating the local folding of the viral DNA and enabling the creation of precise and reproducible shapes.
In her book The Century of the Gene, philosopher of science Evelyn Fox Keller noted that “recent developments in molecular biology have given us new appreciation of the magnitude of the gap between genetic information and biological meaning”. This is a subtle critique of the reduction of the complexity of living organisms to the simplicity of genetic “language”, highlighting how the relationship between matter and information is often much more complex than we give it credit for. And, in its own way, DNA nanotechnology is also contributing to our understanding of the gap between information and meaning. DNA “encodes” information in the form of a molecular sequence; however, the way the same information is expressed differs depending on the larger material environment in which the molecule is located.
What happens when we take DNA out of its biological context? Does that information retain or change its meaning? Maybe asking these questions - and answering them through technology - is part of a necessary demystification of genetic determinism as a universal law of nature. Meaning is not just synonymous with information: it is produced only when information becomes embodied in a larger material system - be it a bacteriophage, a smiley face, or you and me.
References:
Rothemund, P. Folding DNA to create nanoscale shapes and patterns. Nature 440, 297–302 (2006).
Benson, E., Mohammed, A., Gardell, J. et al. DNA rendering of polyhedral meshes at the nanoscale. Nature 523, 441–444 (2015).
Evelyn Fox Keller. The Century of the Gene. Harvard University Press, Cambridge, 2002.