Melding Biology and Chemistry in a ‘Bionic Leaf’

9:40 minutes

A conceptual image of the 'bionic leaf.' Credit: Jessica Polka, Harvard Medical School
A conceptual image of the ‘bionic leaf.’ Credit: Jessica Polka, Harvard Medical School

By combining advanced catalysts with engineered bacteria, researchers have developed a “bionic leaf” that can produce hydrocarbon fuels such as isopropanol and isobutanol from solar energy, water, and carbon dioxide—and it can do it more efficiently than natural photosynthesis. “Biology is the best chemistry,” says Pamela Silver, a professor of systems biology at Harvard Medical School and co-developer of the bionic leaf. Though still in a laboratory-scale, proof-of-concept phase, Silver hopes that systems like the bionic leaf could provide a versatile platform for producing a range of useful chemicals.

Segment Guests

Pamela Silver

Pamela Silver is the Elliot T and Onie H Adams Professor of Biochemistry and Systems Biology at Harvard Medical School, and is a member of the Wyss Institute of Biologically Inspired Engineering at Harvard University, in Cambridge, Massachusetts.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. You know, plants have an amazing ability– taking light from the sun, a little water from the rain, a few minerals from the soil, CO2 from the air, and turning those things into, say, a juicy tomato. Well, now researchers have found a way to combine chemistry and biology to mimic that photosynthetic process in a bionic leaf that in some measurements can beat plants at their own game. Though it doesn’t make tomatoes, but liquid fuel.

Joining me now to talk about the bionic leaf and the intersection of biology and chemistry is Pamela Silver. She’s professor of biochemistry and systems biology at Harvard Medical School and is a member of the Wyss Institute of Biologically Inspired Engineering at Harvard in Cambridge. Welcome back to Science Friday, Dr. Silver.


IRA FLATOW: Let’s go right to it then. Does it look like a leaf?

PAMELA SILVER: Everyone asks me that. When journalists come to the lab, they say, can we see it? Can we look at the leaf?

Unfortunately, it looks like science. It looks like a science experiment. It’s a jar with a bunch of wires coming out of it.

IRA FLATOW: But it’s got a lot of potential, right?

PAMELA SILVER: Absolutely. I actually traveled with it. I took it to a commencement speech as a show and tell.

IRA FLATOW: You did?


Here she comes again. Well, we talked with your–

PAMELA SILVER: Little problem getting it on the plane, by the way.

IRA FLATOW: Oh, gosh. I guess you would have to get that through security. It’s a leaf. I’ll tell you, it’s a leaf, not toothpaste.

We talked with your collaborator, Dan Nocera a few years ago about something he called an artificial leaf. Now, what’s the difference between that and your bionic leaf?

PAMELA SILVER: So the bionic leaf actually begins with the artificial leaf, as Dan invented a process whereby you can go directly from electricity via sunlight to electrodes that carry out what’s called the water splitting reaction. And this is the key reaction in photosynthesis that generates hydrogen and oxygen. So Dan invented the artificial leaf that makes hydrogen.

Now there was a dream that hydrogen could be a fuel, and that still may come true some day. But what we did was then to interface the artificial leaf with nature. And there are these really cool microbes that can eat hydrogen and fix CO2 and make stuff. So by putting the artificial leaf together with nature, we created the bionic leaf.

IRA FLATOW: So you basically built something to feed the bacteria?

PAMELA SILVER: Dan built the artificial leaf, which provides the hydrogen.


PAMELA SILVER: The CO2 comes from air–


PAMELA SILVER: –and everyone’s happy.


IRA FLATOW: And this system can do it more efficiently than plants can?

PAMELA SILVER: That’s right. The combination of– well, so first there are problems with photosynthesis. I think it’s the grand challenge is how do you make plants better? And we’ve done that by using this chemistry of the artificial leaf, which doesn’t generate any toxins the bacteria can grow, and they can use all the hydrogen that’s being provided.

So in that way, we can beat photosynthesis. We get about 10% efficiency of harvesting of light as measured by making it into stuff. And you mentioned that we make fuels. We also make plastics.

IRA FLATOW: And so you’re doing– well, photosynthesis is like 1% efficiency. So you’ve got 10 times the output–


IRA FLATOW: –of stuff?

PAMELA SILVER: Plants are about 1%. Plants are about 1%. Algae is sort of the gold standard up there at around 6%, so we’re beating them all.

IRA FLATOW: Wow. Does it need anything special in terms of infrastructure? In other words, do you need a pipe to pipe in concentrated C02, or is it just sitting out there on your lab bench?

PAMELA SILVER: It’s more or less just sitting in my lab. It’s special. We had to build it. Dan makes these awesome electrodes that can provide the hydrogen. They sit down in a jar. The jar has to be sterile so you don’t get contamination.

And we do pipe in CO2, but it actually will do it with air as well. We don’t necessarily have to provide CO2. I don’t know. It doesn’t– like I said, it doesn’t look super impressive, but it’s really performing well.

IRA FLATOW: All right. Well, let’s to talk about the practicalities then. How do you scale it up, or what kind of engineering do you need to do?

PAMELA SILVER: Well, so in the laboratory, it’s small. It works at about 100 milliliters. In fact, I got a really cute letter from a seventh grader asking if they could build their own bionic leaf, and it occurred to me that we could actually give these to schools and they could test them out.

We’ve been able to scale it about tenfold in the laboratory, so that’s pretty good. It can still sit on the lab bench. That’s a liter. Going beyond that is really a job for chemical engineers, and the good news here is that it is not composed of particularly expensive materials, and the materials are not rare.

IRA FLATOW: You talked about using engineered bacteria to make a fuel, and you said plastics also. Can you make other stuff? Can the bacteria make other stuff?

PAMELA SILVER: Sure. That’s the beauty– that, for me, is the beauty of the system. And the thing I’m excited about is that in fact biology is the best chemistry. It can do things that chemists in the laboratory can’t do, and we call this synthetic biology.

You’ve talked about this on the show before. The ability to engineer organisms, to do this chemistry to make in essence almost anything that’s, for example, carbon based. And that’s our dream is what can we make with these different organisms, and what kinds of organisms can we interface with the leaf?

IRA FLATOW: So what you’re basically doing is equipping these bacteria, which can make whatever you’d like to engineer them to do, with a source of food, basically? By the leaf?

PAMELA SILVER: And it’s important to remember that this does not compete with land, because the bacteria, they can sit there in my laboratory and they can get fed the energy, the electricity from the solar panel sitting on the roof. So it’s really a modular system. The two can be separated.

IRA FLATOW: So where do you go from here now with this?

PAMELA SILVER: As I said, personally, I want to expand the system in its diversity of what it can make. There’s further optimization that can be done to make it so that it’s more compatible with different conditions in the water, increasing the output of hydrogen– this is Dan’s side of the project. And we’re very interested more in optimizing the biology and increasing that diversity at the biological end.

IRA FLATOW: And do you have to genetically modify the bacteria to make what you’d like it to make?

PAMELA SILVER: Sure, the bacteria are highly programmed. Although, in the case of plastics, the particular bacteria that we use– it’s called Ralstonia. It’s a soil bacteria– it’s actually an industrial organism already, because it makes a plastic precursor called PHB. And companies already use this as one of the major sources of this plastic precursor to make biodegradable plastics, so it does that naturally.

However, we can engineer it further, and in this case, we engineered it to make alcohols that can be burned as fuels. But as I said, the ability to engineer biology is amazing now, and so we can start to think about making higher value commodities, have it make food to feed other organisms. We’re preparing a NASA grant now where we think we might be able to use it in space. This is what we’re thinking.

IRA FLATOW: Wow, that sounds terrific. Wow. You know, it is kind of like, where can I get one of my own to have fun with this thing.

PAMELA SILVER: I was thinking about a DIY experiment thing where we gave them to people.

IRA FLATOW: I think– yeah. Maybe there is some sort of Kickstarter thing.


IRA FLATOW: Well, if you’re taking CO2 out of the atmosphere and you’re making fuel out of it, are you taking more out of the atmosphere than you’re putting back in when you use the fuel?

PAMELA SILVER: No, this is the whole premise around biofuels is that they’re carbon neutral. That you recover CO2, you make it into stuff, if it’s fuel, and then you burn it. So the equation around CO2 remains neutral.

IRA FLATOW: Well, we’re going to have to have you back when you make some more headway. And when you have–

PAMELA SILVER: Oh, we will.

IRA FLATOW: –when you have one I can make myself here.

PAMELA SILVER: There’s another story coming soon.

IRA FLATOW: Oh, is there? Can you give us a little hint? Come on, no one’s listening.


IRA FLATOW: It’s just you and me.

PAMELA SILVER: Just thinking about plants.


PAMELA SILVER: Real plants.

IRA FLATOW: Is there a science fiction movie– this won’t grow out of the beaker somewhere in your desk and take over–

PAMELA SILVER: That’s the thing. It’s not growing. The bacteria are growing, but it needs this special electrode in order to promote growth. I think what I have to do is make one that looks like a leaf to satisfy all you.

IRA FLATOW: Absolutely. It’ll get those TV–

PAMELA SILVER: We’ll work on that.

IRA FLATOW: –cameras in there so fast.

PAMELA SILVER: Absolutely.

IRA FLATOW: All right, Dr. Silver. Thank you very much for taking time to do this today.


IRA FLATOW: Pamela Silver is a professor of biochemistry and systems biology at Harvard Medical School and is a member of the Wyss Institute of Biologically Inspired Engineering– I kind of think of our show like that– at Harvard in Cambridge.

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