Origami Goes 'Nano'

Origami, from ori meaning “folding”, and kami meaning “paper”, is an ancient Japanese art form. But DNA Origami? It’s origami gone molecular- and nano-scale. DNA origami can be used to make super-cool three-dimensional shapes out of nanoparticles with rather ‘light-ning’ results.

“Matter structured on a length scale comparable to or smaller than the wavelength of light can exhibit unusual optical properties.”

long nanohelix.jpg So starts a Letter in Nature magazine this March 15th, 2012. Anton Kuzyk and colleagues have used DNA origami to guide gold nanoparticles to self-assemble into helical 3-dimensional structures… similar to the ‘curly’ structure of a DNA helix! (See image to the right). The gold nanoparticles (black) that ‘wrap’ around the DNA origami bundle structure (white cylindrical structure) measure in at less than 10 nanometers in diameter – or less than 1000x smaller than the width of a typical strand of human hair. Gold nanoparticles are known as plasmonic structures, so called because they interact with light in unique and unusual ways. While gold nanoparticles typically exist in a solution as single particles floating around at random (you can see some ‘loners’ in the image), Kuzyk and colleagues have used DNA origami to ‘bridle’ these bucking bronco gold nanoparticles and steer them into precise three-dimensional structures that look like tiny ‘spring coils’.

These tiny nanoparticle coils interact with light in ways that single nanoparticles don’t. Helical plasmonic nanostructures interact differently with light that is polarized in different directions (think of a wave of light rotating in one direction or another when traveling through the air – these are different polarizations of the light.)

A. Left- and right-handed nanohelices formed by nine gold nanoparticles attached to the surface of DNA origami 24-helix bundles. B. Electron microscope image of assembled left-handed gold nanohelices (scale bar, 100 nm). C. nanohelices interact differently with left-hand-circularly polarized (LCP) and right-hand-circularly polarized (RCP) light.

Helix bundles.jpg DNA origami, originated by Paul Rothemund at the California Institute of Technology, consists of folding long pieces of DNA, the genetic or hereditary material of our cells, into 2- and 3-dimensional structures. This would be similar to folding a thin strip of paper into a complex structure like a paper swan or a paper airplane. DNA is particularly good for molecular-scale origami because the 4 bases of DNA – Adenine, Guanine, Cytosine, and Thymine – pair up to help complementary pieces of DNA hybridize or stick together. With enough sticky pieces of DNA, researchers can create amazing 3-dimensional structures, like the cylindrical 24-helix bundles used by Kuzyk and colleagues to guide the self-assembly of helical nanoparticle structures (see multi-helix DNA origami bundles in image to the right).

I asked Anton Kuzyk, Postdoctoral Researcher at Aalto University School of Science, to tell me a bit more about his work.

1) What is DNA Origami, in layman’s terms, and how is this allowing nanostructures to be assembled in chiral shapes?

DNA origami is a technique developed in 2006 by Paul Rothemund for assembly of DNA nanostructures. The technique is based on the sequence-specific binding of hundreds of short synthetic DNA “staple” strands to a long single-stranded DNA scaffold molecule and allows for high yield, reproducible and programmable creation of nanostructures of almost arbitrary shapes. One the neat things about DNA origami structures is that they can serve as ‘nanobreadboards’, i.e., templates for arrangement of (functional) nanocomponents (metal nanoparticles, quantum dots, proteins, etc) with nanometer accuracy, which is often not achievable with other state of the art fabrication techniques. – Kuzyk

In other words, these DNA origami shapes can be used to create 3-dimensional shapes out of nanoparticles by sticking the particles at particular locations on the origami shape!

2) What are some of the implications of being able to assemble plasmonic nanoparticles in helical geometries?

It’s important to realize that helical arrangement are not of crucial importance. We chose helical geometry because it’s three dimensional and esthetically pleasing. More important is the ability to arrange plasmonic particles with high precision into predesigned configuration. The spatial arrangement results in new optical property (optical or light activity) which comes from collective interaction between particles. One can think about our structures as artificial plasmonic “molecules”. As in chemistry, molecules often have properties which are very different from properties of the single atoms that they are built from. Our helices are plasmonic “molecules” built from plasmonic “atoms” (single gold nanoparticles). These plasmonic “molecules” have (optical) properties that single atoms don’t. Specifically, our helices are optically active and interact in different ways with differently polarized light. Another important aspect of our work is that we can predict and tune the properties of these plasmonic “molecules”. – Kuzyk

In other words, the helical multi-nanoparticle shapes that his group built using DNA origami are important because they show that it is possible to assemble gold nanoparticles into shapes that take on new optical properties that the single gold nanoparticles, on their own, don’t have.

3) What are some of the applications for this technology? Why would we want to use DNA-origami assembled nanoparticle structures (other than that they just sound super cool)?!

Our work greatly expands the toolbox available for creation of metal nanostructures. Due to their surface Plasmon resonances, metal nanostructures can be used to manipulate light on very small length scale. This, in turn, makes them very promising candidates for applications which require highly localized [light]. To name a few, possible applications are sensing in medical and environmental fields, high resolution imaging and information processing and information transfer. It still remains to be seen in which area our method will turn out to be the most useful. – Kuzyk

We look forward to seeing real-world applications develop! Until then… keep folding!

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1. Supplementary Figure S10, Nature 483, 311-314 (15 March 2012) doi:10.1038/nature10889

2. Figure 1, Nature 483, 311-314 (15 March 2012) doi:10.1038/nature10889

3. Figure 3: Packing and cross-over spacing rules for multilayer DNA origami. Nature Methods 8, 221-229 (2011) doi:10.1038/nmeth.1570

Kuzyk, A., Schreiber, R., Fan, Z., Pardatscher, G., Roller, E., Högele, A., Simmel, F., Govorov, A., & Liedl, T. (2012). DNA-based self-assembly of chiral plasmonic nanostructures with tailored optical response Nature, 483 (7389), 311-314 DOI: 10.1038/nature10889