In Significant Advance for Artificial Photosynthesis, a Machine and Living Bacteria Work Together to Make Fuel

Scientists say they have merged living organisms with nanotechnology to mimic the photosynthesis plants use to make energy.

Blending chemistry, biology and materials science, the team from the University of California, Berkeley and Lawrence Berkeley National Laboratory created a living-synthetic hybrid system. The process brings together nanowires and bacteria (seen in the image above) to convert sunlight, water and carbon dioxide in the air into valuable chemicals like liquid fuel, plastics and pharmaceuticals.

Like plants, the system uses solar power to make complex molecules from simple ones. In contrast to the carbohydrates and oxygen that are the product of natural photosynthesis, the new device converts CO2 into acetate, which is the building block for a number of industrially useful chemicals.

“We believe our system is a revolutionary leap forward in the field of artificial photosynthesis,” said Peidong Yang, a Berkeley Lab chemist who was one of the project leaders. “Our system has the potential to fundamentally change the chemical and oil industry in that we can produce chemicals and fuels in a totally renewable way, rather than extracting them from deep below the ground.”



The group harnessed the semiconducting property of silicon and titanium dioxide nanowires to convert solar energy into free electrons, which are then taken up by an anaerobic bacterium called Sporomusa ovata that live among the wires. S. ovata use this energy to convert CO2 into acetic acid, the sour-tasting component in vinegar. This simple acetate is then fed to genetically engineered E. coli bacteria, which synthesize more complex and useful molecules.

If they can scale the system up, it potentially represents two big advances for humans and the environment. The system produces chemicals that typically require petroleum products to be made. It also makes those chemicals by pulling in CO2, which now exists in overabundance in our atmosphere and is a contributor to climate change. The scientists say a device that harnesses the system they’ve created could be used to capture CO2 before it leaves smokestacks.

(This break-through artificial photosynthesis system has four general components: [1] harvesting solar energy, [2] generating reducing equivalents, [3] reducing CO2 to biosynthetic intermediates, and [4] producing value-added chemicals. Illustration courtesy of Liu et al./Lawrence Berkeley Lab/Nano Letters.)

Researchers have already pushed their system to convert sunlight at roughly the same efficiency as living plant leaves. They are optimistic that they will be able to push it up to a solar-to-chemical conversion efficiency of 10 percent, which they say will make it commercially viable.

“We demonstrate that a hybrid semiconductor nanowire–bacteria system can reduce CO 2 at neutral pH to a wide array of chemical targets, such as fuels, polymers, and complex pharmaceutical precursors, using only solar energy input,” the team write in their study. “As such, interfacing biocompatible solid-state nanodevices with living systems provides a starting point for developing a programmable system of chemical synthesis entirely powered by sunlight.”



The team’s work is described in a recent study published in the journal ACS Nano Letters.

Top Image: Cross-sectional scanning electron microscopy image of the nanowire/bacteria hybrid array used in a revolutionary new artificial photosynthesis system. Bacteria of the species S. ovata live amongst the semiconducting nanowires that deliver them electrons. Courtesy of Liu et al./Lawrence Berkeley Lab.