Using DNA To Shape Nanostructures

Chemists and materials scientists are trying to learn to build ultra-small, precisely ordered structures for use in optics, electronics, and other applications. Writing in the journal Science, Chad Mirkin and colleagues describe a way to use snippets of DNA to tailor the shape and size of crystal structures, tweaking them to fit specific uses.

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IRA FLATOW, host: This is SCIENCE FRIDAY. I'm Ira Flatow. You normally think of DNA as being the molecule that controls the building blocks of life. But what if DNA could control real, physical building blocks, make stuff out of them? Now researchers say they've come up with a way to use DNA to coax tiny nanoparticles into making new, completely artificial materials.

Chad Mirkin is one of the authors of a research paper in the journal Science that describes just how to do that. He is a professor of chemistry and director of the International Institute for Nanotechnology at Northwestern University in Evanston, Illinois. Welcome to SCIENCE FRIDAY.

CHAD MIRKIN: Thank you very much.

FLATOW: So are you basically saying that you can program DNA to build things for you?

MIRKIN: That's - well, we can program DNA and building blocks to do that. So the idea here is to take tiny bits of matter, nanoparticles, and to attach strands of DNA that have a preconceived and designed code that then guides them through an assembly process based upon known DNA recognition properties to assemble into macroscopic structures that have properties that are defined by the arrangement of those particles within the extended structure.

FLATOW: So do you actually code the DNA the way you'd like the product to wind up?

MIRKIN: That's the beauty of it. So, you know, as chemists, we normally synthesize things from atoms. We take atoms and put them together with bonds to make molecules. Molecules, then, are put together to form materials. Here we have a new type of, you know, called programmable atom that's much more programmable than the types of atoms that nature gives us.

We have a particle that can be one of many different types of compositions, a gold nanoparticle, a silver nanoparticle, things called quantum dots, which have all sorts of spectacular optical properties, magnetic structures, anything you'd like. And then you can attach strands of DNA to the surface of these particles and give them a code that's unique to each particle that you design and has a complementary particle that it recognizes and a solution that you've designed ahead of time.

And when they encounter one another, they form a duplex, the famous double-helix that then joins them together. And that bond is also programmable because we can increase the length or decrease the length of it and control the strength of it based upon the choice of DNA sequence.

FLATOW: Wow, I don't think people ever thought about, you know, choosing the right DNA sequence to come up with the product that you want.

MIRKIN: Yeah, it's really kind of a neat concept. It's one we introduced, actually, about 15 years ago, in an early article in Nature in 1996. But we didn't know how to make the particles form different crystal lattices. We could zip them together, but we couldn't get them adopt the perfect structure that we were after, a design structure, let's say, one that mimicked table salt, sodium chloride or diamond.

We now know how to do that, and what this paper really does, it doesn't introduce that idea. That idea, as I said, has been around now for about 15 years. But it introduces the set of design rules that allow scientists to systematically make almost any structure that they'd like with completely tailorable what we'd call lattice parameters.

FLATOW: Give me an example of the kinds of things.

MIRKIN: Well, as I said, so if you wanted to have a structure where you had an arrangement that's similar to the way atoms are arranged in table salt, you could do that; the way atoms are arranged in diamond, you could do that; in silicon; really anything you'd like based upon these sets of design rules that dictate what the governing principles are in terms of guiding the assembly process and controlling which particles surround others in the solution containing similar entities.

FLATOW: Can you make substances that never existed before?

MIRKIN: Well, all of these substances never existed before because they're made out of these nanostructures, and they have this tailorable structure so that the pattern has existed before, in many cases, but the actual composition is brand new.

But in addition to that, we can make arrangements of particles where there is no mineral equivalent, where, you know, it truly is an example of, you know, man over nature in this case where, by creating these programmable atoms, if you will, we can make lots of structures that make sense from a geometric standpoint, but we don't have chemical or mineral equivalents.

FLATOW: Well, apart from the elegance of what you've been able to do, what kinds of practical items could come out of it?

MIRKIN: Well, it's early there, but there already are examples of practical items coming out of the atomic-scale building blocks, or what we're calling the nanoparticle building blocks that I've been describing. They're the basis for diagnostic systems, for example, medical diagnostic systems, probes that are used in high-sensitivity assays for biomarkers associated with disease.

So a company we started, called Nanosphere, that's commercialized them over the last 10 years, they're beginning to be used now for all sorts of therapeutic applications. There's a new start-up company called Arosense(ph) that is now beginning to use these types of particles for very powerful forms of gene regulation.

But I think that's really just the tip of the iceberg, so to speak. I think that this is a fundamentally new way of thinking about building materials, and materials are important to almost every application that we take for granted, whether we're talking about electronics, optics, biomedical applications, even examples where we're interested in things like solar energy harvesting and energy conversion and storage.

The ability to take tiny building blocks and arrange them with sub-nanometer precision in three-dimensional space with total control over the types of building blocks and, as I said, all the lattice parameters, the distances between them is going to create a pathway to realizing a whole new class of materials that I think are going to have many important applications.

But this is really the starting point, and the future will tell the whole story.

FLATOW: 1-800-989-8255 is our number. You can also tweet us @scifri, @-S-C-I-F-R-I. Just so I can tweeze this out a little bit more so that people can understand what's happening, would it be right, correct to say that you're making something synthetic that used to be made naturally, for example, you know, using - you're making your own molecules but let's say with nanoparticles as atoms and DNA as the bonds between them?

MIRKIN: It's more the analogy that matters here in the sense that we're taking inspiration from nature. We're not making anything that nature makes, but we're taking inspiration from nature, the fact that we now know what the double-helix is made of, and the base pairing that occurs within.

We're using chemistry to synthesize components of that structure and attaching them to a natural structure, materials, as you said, physical entities, and then using those recognition properties to build a larger structure, and in this case the properties of the larger structure depend upon where the different particles go.

FLATOW: Let's go to the phones, 1-800-989-8255. Drew(ph) in Cincinnati, hi, welcome to SCIENCE FRIDAY.

DREW: Hey there, great to talk to you guys. I actually used to work at Center for Nanospace Material Science in Oak Ridge National Laboratory. And part of my time there was spent trying to study the health and safety aspects of working with nanoparticles.

And at this current moment, I know there is no real conclusive evidence on the effects of nanoparticles just because they're very new and, you know, it's very tough to study long-term things that haven't been around for very long.

And I was wondering if there's been any insight recently into whether or not these particles are safe to work with, if there's been any negative or even positive health, like, benefits from working with nanoparticles.

FLATOW: All right, thanks for calling, Michel.

MIRKIN: It's a good question. It's an often-asked question. It's a tough one to answer because nanotech is so broad in terms of definition. So it really depends upon the class of materials that you're referring to. In this case, much of what we're doing involves gold nanoparticle structures, especially the biomedical applications that I was alluding to.

Gold is a fairly chemically inert material. In certain cases, in actually many cases, they've even used it in therapies, for arthritis, for example. It seems to be a material that is fairly innocuous and shows some extremely beneficial properties in terms of developing biodiagnostic tools or medical diagnostic tools that allow us to track disease in early states.

And in the case of therapies, we've created a new way of actually using them to affect gene regulation in a very - what appears preliminarily as a very safe and very powerful way. And so when you talk about health benefits, I think they could be enormous because if you could design - make designer materials that could dramatically change the way we treat disease and get it at its genetic roots using these types of nanomaterials, that would be an enormous win.

FLATOW: You've been a pioneer in lots of different ways. You are one of the most cited authors out there. Tell us about some of the other things going on in your lab.

MIRKIN: Oh, lots of things. I mean, everybody asks, you know, what's your favorite? There's so many different things going on in the lab. We've developed, as I said, not only these biodiagnostic and therapeutic tools but high-resolution lithographic tools, ways of doing nanoprinting. We invented the technology dip-pen nanolithography, which is now a commercialized tool used all over the world.

But we keep pushing the development of that. And we now have effectively created a system that allows you to print structures that would have to be printed using a - tens of millions of dollars worth of equipment in terms of microfabrication at the point of use. We call it desktop fab, you know, the equivalent of a desktop printer.

FLATOW: Like 3-D printing.

MIRKIN: Well not just 3-D, this would be two-dimensional printing, but on a very fine scale. We just had some visitors from Microsoft, for example. Craig Mundie came and visited our lab and gave a wonderful lecture. In real time, we made the world's smallest Microsoft logo, one molecule high, 75-nanometer dot resolution. It was pretty extraordinary, you know, while he's standing there.

That's a type of thing that might be able to be made by other tools, although I'd argue actually it would be difficult if you made it out of the types of materials that we made it out of. But it certainly couldn't be done in real time at the point of use and for instrumentation now is relatively cheap by instrument and research user standards.

FLATOW: So where do you go from here with the work you're publishing today? What's the next step?

MIRKIN: Well, there's a fundamental aspect to it. Much of what we do focuses on really getting at what I think is the major problem in this area, and that is developing analytical tools and chemistry to make and manipulate structures on the sub-100-nanometer length scale. That's really what our whole research has been about.

But then every time we do that, we often discover new materials and new techniques that can be translated into the development of powerful new technologies, and in this area that we started out talking about today, I see incredible promise in the use of these types of materials in intracellular gene regulation, in the development, as I said, of powerful new medications, pharmaceutical reagents, for example, that can treat many debilitating disease.

We have several programs focused on a variety of different types of cancer types and a lot of promising results not just in cellular models but in animal models. And I think that's exciting.

FLATOW: Well, we also have lots of promises. We'll have to see how it shakes out. Thank you very much. Thanks, Chad, for joining us.

MIRKIN: Thank you.

FLATOW: Chad Mirkin is the George B. Rathmann Professor of Chemistry and director of the International Institute for - get the mouth to work today - Nanotechnology at Northwestern University in Evanston, Illinois. We're going to take a break, and when we come back, we're going to talk about, well, building a toaster, now not just any toaster, you know, you could get a Heathkit and build it from parts. This is totally from scratch.

You have to go out and ore - mine the ore yourself, smelt it. We'll get into it. Believe me, it's not a pretty picture when it's done, but it's an interesting project, and the author of a new book about the Toaster Project will be with us. You stay with us. We'll be right back after this break.

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FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY, from NPR.

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