Bio Focus: Hybrid semiconductor-bacterium self-photosensitization improves artificial photosynthesis
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o Focus Hybrid semiconductor-bacterium self-photosensitization improves artificial photosynthesis
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esearchers from the University of California–Berkeley and Lawrence Berkeley National Laboratory have developed a hybrid system for artificial photosynthesis by combining nanoparticles of an inorganic semiconductor with selfphotosensitizing bacteria to produce acetic acid using only solar energy. Kelsey K. Sakimoto, Andrew Barnabas Wong, and Peidong Yang combined nanoparticles of the semiconductor cadmium sulfide (CdS), which is an excellent harvester of light, with a self-photosensitizing bacteria Moorella thermoacetica. The nanoparticles were precipitated on the surface of the bacteria, ensuring biocompatibility and a strong interface. These results are reported in a recent issue of Science (DOI: 10.1126/science.aad3317). In natural photosynthesis, solar energy is used to oxidize water to oxygen and reduce carbon dioxide to make the chemicals that sustain life. Semiconductors are better at absorbing solar radiation than biological materials, but cannot compete with biocatalysts in terms of specificity, cost, or their ability to self-replicate and repair. By combining both, one can then achieve the best of both worlds. Nonphotosynthetic bacteria are preferred in synthetic biology because they can produce a variety of products by reducing CO2. For this study, the researchers chose Moorella thermoacetica, which is a nonphotosynthetic bacteria. They added cadmium nitrate and cysteine—a source of sulfur—to the growing culture so that CdS could be precipitated on the surface
dots was only tested against one cell line and a transformed cell line that is not an accurate representation of the numerous healthy cells in our body,” Webster said, adding that Cd and Te also have toxicity concerns that need to be monitored in future studies (the researchers used a low dose of CdTe to minimize its harmful effects).
“Moving forward, we are refining the design of our nanoparticles,” Chatterjee said. “We are trying to push the limit of how far can we go in designing new therapies and making nanoparticles safer.” Eventually, the team hopes to conduct clinical trials using these quantum dots. Joseph Bennington-Castro
of the bacteria. Scanning electron microscopy, scanning transmission electron microscopy, and energy-dispersive x-ray spectroscopy confirmed the presence of CdS particles with sizes of under 10 nm. The self-photosensitization of the nonphotosynthetic bacteria was induced with the cadmium sulfide nanoparticles, enabling the photosynthesis of acetic acid. A maximum yield of 90% acetic acid, as a natural waste product of respiration, was obtained. The cell counts of the Moorella thermoacetica-CdS system nearly doubled after a day, demonstrating that this self-reproducing hybrid organism can be sustained purely through solar energy. Under blue light (wavelength 435–485 nm) the quantum yield (defined as rate of production of acetic acid per unit of photon flux) was 52% ± 17%, as compared with the 22% reported previously for an
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