Harvesting solar fuels thanks to the unusual appetite of a bacteria for gold – ScienceDaily

M. thermoacetica debuted as the first non-photosensitive bacterium to perform artificial photosynthesis as part of a study conducted by Peidong Yang, a professor at the College of Chemistry of the University of Berkeley at the University of California. UC Berkeley. By attaching light-absorbing cadmium sulfide (CdS) nanoparticles to the outside of the bacterial membrane, researchers turned M. thermoacetica into a tiny photosynthesis device that turns sunlight and carbon dioxide into useful chemicals.

Now, Yang and his team of researchers have found a better way to attract this CO₂Hungarian bacteria to become even more productive. By placing light-absorbing gold nanoclusters inside the bacteria, they have created a biohybrid system that produces a higher chemical yield than previously demonstrated. The research, funded by the National Institutes of Health, was published on October 1 in Nature Nanotechnology.

For the first hybrid model, M. thermoacetica-CdS, researchers chose cadmium sulfide as a semiconductor for its ability to absorb visible light. But since cadmium sulphide is toxic to bacteria, the nanoparticles had to be attached to the cell membrane "extracellularly" or outside the M. thermoacetica-CdS system. Sunlight excites each nanoparticle of cadmium sulphide by generating a charged particle called an electron. When these electrons generated by the light pass through the bacteria, they interact with several enzymes during a process called "CO₂ reduction ", triggering a cascade of reactions that eventually transform the CO₂ in acetate, a valuable chemical for the manufacture of solar fuels.

But in the extracellular model, the electrons end up interacting with other chemicals that play no role in the transformation of CO₂ in acetate. And as a result, some electrons are lost and never reach the enzymes. Thus, to improve what is called "quantum efficiency" or the ability of the bacteria to produce acetate whenever it gains an electron, the researchers discovered a other semiconductor: nanoclusters composed of 22 gold atoms (Au22), a material that M. thermoacetica took surprisingly. shine at.

"We chose Au22 because it is ideal for absorbing visible light and that it is likely to generate CO₂ "We examined under the microscope, we found that the bacteria was responsible for these clusters Au22 – and that she was still alive."

The M. thermoacetica-Au22 imaging system was performed at the UC Berkeley Molecular Imaging Center.

The researchers also selected Au22 – nicknamed by the researchers – as "magical" gold nanoclusters – for its ultra-fine size: a single Au22 nanocluster has a diameter of 1 nanometer, allowing to each nanocluster to slide easily through the bacterial cell wall.

"By feeding the bacteria with Au22 nanoclusters, we have effectively streamlined the process of electron transfer for CO₂ the reduction pathway inside the bacterium, as evidenced by a quantum efficiency of 2.86% – or 33% additional acetate in the M. thermoacetica-Au22 system compared to the CdS model, "Yang said.

The magical gold nanocluster is the latest discovery of Yang's lab, which has focused for six years on the use of biohybrid nanostructures to convert CO.₂ in useful chemicals as part of a continuing effort to find affordable and abundant resources for renewable fuels and potential solutions to counter the effects of climate change.

"We then want to find a way to reduce costs, improve the life of these biohybrid systems and improve quantum efficiency," Yang said. "Continuing to examine the fundamental aspect of the photoactivation of gold nanoclusters and following the process of electron transfer within the CO₂ way of reduction, we hope to find even better solutions. "

The co-authors with Yang are Hao Zhang, a graduate student from the University of Berkeley, and Hao Liu, a former postdoctoral fellow, currently at the Donghua University in Shanghai, China.