Subtitles and Transcript
0:11 I thought I would talk a little bit about how nature makes materials. I brought along with me an abalone shell. This abalone shell is a biocomposite material that's 98 percent by mass calcium carbonate and two percent by mass protein. Yet, it's 3,000 times tougher than its geological counterpart. And a lot of people might use structures like abalone shells, like chalk. I've been fascinated by how nature makes materials, and there's a lot of sequence to how they do such an exquisite job. Part of it is that these materials are macroscopic in structure, but they're formed at the nanoscale. They're formed at the nanoscale, and they use proteins that are coded by the genetic level that allow them to build these really exquisite structures.
0:53 So something I think is very fascinating is what if you could give life to non-living structures, like batteries and like solar cells? What if they had some of the same capabilities that an abalone shell did, in terms of being able to build really exquisite structures at room temperature and room pressure, using non-toxic chemicals and adding no toxic materials back into the environment? So that's the vision that I've been thinking about. And so what if you could grow a battery in a Petri dish? Or, what if you could give genetic information to a battery so that it could actually become better as a function of time, and do so in an environmentally friendly way?
1:31 And so, going back to this abalone shell, besides being nano-structured, one thing that's fascinating, is when a male and a female abalone get together, they pass on the genetic information that says, "This is how to build an exquisite material. Here's how to do it at room temperature and pressure, using non-toxic materials." Same with diatoms, which are shown right here, which are glasseous structures. Every time the diatoms replicate, they give the genetic information that says, "Here's how to build glass in the ocean that's perfectly nano-structured. And you can do it the same, over and over again." So what if you could do the same thing with a solar cell or a battery? I like to say my favorite biomaterial is my four year-old.
2:09 But anyone who's ever had, or knows, small children knows they're incredibly complex organisms. And so if you wanted to convince them to do something they don't want to do, it's very difficult. So when we think about future technologies, we actually think of using bacteria and virus, simple organisms. Can you convince them to work with a new toolbox, so that they can build a structure that will be important to me?
2:32 Also, when we think about future technologies, we start with the beginning of Earth. Basically, it took a billion years to have life on Earth. And very rapidly, they became multi-cellular, they could replicate, they could use photosynthesis as a way of getting their energy source. But it wasn't until about 500 million years ago -- during the Cambrian geologic time period -- that organisms in the ocean started making hard materials. Before that, they were all soft, fluffy structures. And it was during this time that there was increased calcium and iron and silicon in the environment, and organisms learned how to make hard materials. And so that's what I would like be able to do -- convince biology to work with the rest of the periodic table.
3:12 Now if you look at biology, there's many structures like DNA and antibodies and proteins and ribosomes that you've heard about that are already nano-structured. So nature already gives us really exquisite structures on the nanoscale. What if we could harness them and convince them to not be an antibody that does something like HIV? But what if we could convince them to build a solar cell for us? So here are some examples: these are some natural shells.
3:36 There are natural biological materials. The abalone shell here -- and if you fracture it, you can look at the fact that it's nano-structured. There's diatoms made out of SIO2, and they're magnetotactic bacteria that make small, single-domain magnets used for navigation. What all these have in common is these materials are structured at the nanoscale, and they have a DNA sequence that codes for a protein sequence that gives them the blueprint to be able to build these really wonderful structures. Now, going back to the abalone shell, the abalone makes this shell by having these proteins. These proteins are very negatively charged. And they can pull calcium out of the environment, put down a layer of calcium and then carbonate, calcium and carbonate. It has the chemical sequences of amino acids, which says, "This is how to build the structure. Here's the DNA sequence, here's the protein sequence in order to do it." And so an interesting idea is, what if you could take any material that you wanted, or any element on the periodic table, and find its corresponding DNA sequence, then code it for a corresponding protein sequence to build a structure, but not build an abalone shell -- build something that, through nature, it has never had the opportunity to work with yet.
4:41 And so here's the periodic table. And I absolutely love the periodic table. Every year for the incoming freshman class at MIT, I have a periodic table made that says, "Welcome to MIT. Now you're in your element." And you flip it over, and it's the amino acids with the PH at which they have different charges. And so I give this out to thousands of people. And I know it says MIT, and this is Caltech, but I have a couple extra if people want it. And I was really fortunate to have President Obama visit my lab this year on his visit to MIT, and I really wanted to give him a periodic table. So I stayed up at night, and I talked to my husband, "How do I give President Obama a periodic table? What if he says, 'Oh, I already have one,' or, 'I've already memorized it'?" (Laughter) And so he came to visit my lab and looked around -- it was a great visit. And then afterward, I said, "Sir, I want to give you the periodic table in case you're ever in a bind and need to calculate molecular weight." And I thought molecular weight sounded much less nerdy than molar mass. And so he looked at it, and he said, "Thank you. I'll look at it periodically." (Laughter) (Applause) And later in a lecture that he gave on clean energy, he pulled it out and said, "And people at MIT, they give out periodic tables."
5:57 So basically what I didn't tell you is that about 500 million years ago, organisms starter making materials, but it took them about 50 million years to get good at it. It took them about 50 million years to learn how to perfect how to make that abalone shell. And that's a hard sell to a graduate student. (Laughter) "I have this great project -- 50 million years." And so we had to develop a way of trying to do this more rapidly. And so we use a virus that's a non-toxic virus called M13 bacteriophage that's job is to infect bacteria. Well it has a simple DNA structure that you can go in and cut and paste additional DNA sequences into it. And by doing that, it allows the virus to express random protein sequences.
6:35 And this is pretty easy biotechnology. And you could basically do this a billion times. And so you can go in and have a billion different viruses that are all genetically identical, but they differ from each other based on their tips, on one sequence that codes for one protein. Now if you take all billion viruses, and you can put them in one drop of liquid, you can force them to interact with anything you want on the periodic table. And through a process of selection evolution, you can pull one out of a billion that does something that you'd like it to do, like grow a battery or grow a solar cell.
7:03 So basically, viruses can't replicate themselves; they need a host. Once you find that one out of a billion, you infect it into a bacteria, and you make millions and billions of copies of that particular sequence. And so the other thing that's beautiful about biology is that biology gives you really exquisite structures with nice link scales. And these viruses are long and skinny, and we can get them to express the ability to grow something like semiconductors or materials for batteries.
7:28 Now this is a high-powered battery that we grew in my lab. We engineered a virus to pick up carbon nanotubes. So one part of the virus grabs a carbon nanotube. The other part of the virus has a sequence that can grow an electrode material for a battery. And then it wires itself to the current collector. And so through a process of selection evolution, we went from being able to have a virus that made a crummy battery to a virus that made a good battery to a virus that made a record-breaking, high-powered battery that's all made at room temperature, basically at the bench top. And that battery went to the White House for a press conference. I brought it here. You can see it in this case -- that's lighting this LED. Now if we could scale this, you could actually use it to run your Prius, which is my dream -- to be able to drive a virus-powered car.
8:15 But it's basically -- you can pull one out of a billion. You can make lots of amplifications to it. Basically, you make an amplification in the lab, and then you get it to self-assemble into a structure like a battery. We're able to do this also with catalysis. This is the example of photocatalytic splitting of water. And what we've been able to do is engineer a virus to basically take dye-absorbing molecules and line them up on the surface of the virus so it acts as an antenna, and you get an energy transfer across the virus. And then we give it a second gene to grow an inorganic material that can be used to split water into oxygen and hydrogen that can be used for clean fuels. And I brought an example with me of that today. My students promised me it would work. These are virus-assembled nanowires. When you shine light on them, you can see them bubbling. In this case, you're seeing oxygen bubbles come out. And basically, by controlling the genes, you can control multiple materials to improve your device performance.
9:14 The last example are solar cells. You can also do this with solar cells. We've been able to engineer viruses to pick up carbon nanotubes and then grow titanium dioxide around them -- and use as a way of getting electrons through the device. And what we've found is through genetic engineering, we can actually increase the efficiencies of these solar cells to record numbers for these types of dye-sensitized systems. And I brought one of those as well that you can play around with outside afterward. So this is a virus-based solar cell. Through evolution and selection, we took it from an eight percent efficiency solar cell to an 11 percent efficiency solar cell.
9:57 So I hope that I've convinced you that there's a lot of great, interesting things to be learned about how nature makes materials -- and taking it the next step to see if you can force, or whether you can take advantage of how nature makes materials, to make things that nature hasn't yet dreamed of making.
10:13 Thank you.