Tag Archives: Yi Yu

Unusual appetite for gold

This bacterium (bacteria being the plural) loves gold, which is lucky for anyone trying to develop artificial photosynthesis.From an October 9, 2018 news item on ScienceDaily,

A bacterium named Moorella thermoacetica won’t work for free. But UC Berkeley [University of California at Berkeley] researchers have figured out it has an appetite for gold. And in exchange for this special treat, the bacterium has revealed a more efficient path to producing solar fuels through artificial photosynthesis.

An October 5, 2018 UC Berkeley news release by Theresa Duque (also on EurekAlert but published on October 9, 2018), which originated the news item, expands on the theme,

M. thermoacetica first made its debut as the first non-photosensitive bacterium to carry out artificial photosynthesis (link is external) in a study led by Peidong Yang, a professor in UC Berkeley’s College of Chemistry. By attaching light-absorbing nanoparticles made of cadmium sulfide (CdS) to the bacterial membrane exterior, the researchers turned M. thermoacetica into a tiny photosynthesis machine, converting sunlight and carbon dioxide into useful chemicals.

Now Yang and his team of researchers have found a better way to entice this CO2-hungry bacterium into being even more productive. By placing light-absorbing gold nanoclusters inside the bacterium, they have created a biohybrid system that produces a higher yield of chemical products than previously demonstrated. The research, funded by the National Institutes of Health, was published on Oct. 1 in Nature Nanotechnology (link is external).

For the first hybrid model, M. thermoacetica-CdS, the researchers chose cadmium sulfide as the semiconductor for its ability to absorb visible light. But because cadmium sulfide 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 cadmium-sulfide nanoparticle into generating a charged particle known as an electron. As these light-generated electrons travel through the bacterium, they interact with multiple enzymes in a process known as “CO2 reduction,” triggering a cascade of reactions that eventually turns CO2 into acetate, a valuable chemical for making solar fuels.

But within the extracellular model, the electrons end up interacting with other chemicals that have no part in turning CO2 into acetate. And as a result, some electrons are lost and never reach the enzymes. So to improve what’s known as “quantum efficiency,” or the bacterium’s ability to produce acetate each time it gains an electron, the researchers found another semiconductor: nanoclusters made of 22 gold atoms (Au22), a material that M. thermoacetica took a surprising shine to.

A single nanocluster of 22 gold atoms

Figure: A single nanocluster of 22 gold atoms – Au22 – is only 1 nanometer in diameter, allowing it to easily slip through the bacterial cell wall.

“We selected Au22 because it’s ideal for absorbing visible light and has the potential for driving the CO2 reduction process, but we weren’t sure whether it would be compatible with the bacteria,” Yang said. “When we inspected them under the microscope, we discovered that the bacteria were loaded with these Au22 clusters – and were still happily alive.”

Imaging of the M. thermoacetica-Au22 system was done at UC Berkeley’s Molecular Imaging Center (link is external).

The researchers also selected Au22 ­– dubbed by the researchers as “magic” gold nanoclusters – for its ultrasmall size: A single Au22nanocluster is only 1 nanometer in diameter, allowing each nanocluster to easily slip through the bacterial cell wall.

“By feeding bacteria with Au22 nanoclusters, we’ve effectively streamlined the electron transfer process for the CO2 reduction pathway inside the bacteria, as evidenced by a 2.86 percent quantum efficiency – or 33 percent more acetate produced within the M. thermoacetica-Au22 system than the CdS model,” Yang said.

The magic gold nanocluster is the latest discovery coming out of Yang’s lab, which for the past six years has focused on using biohybrid nanostructures to convert CO2 into useful chemicals as part of an ongoing effort to find affordable, abundant resources for renewable fuels, and potential solutions to thwart the effects of climate change.

“Next, we’d like to find a way to reduce costs, improve the lifetimes for these biohybrid systems, and improve quantum efficiency,” Yang said. “By continuing to look at the fundamental aspect of how gold nanoclusters are being photoactivated, and by following the electron transfer process within the CO2 reduction pathway, we hope to find even better solutions.”

Co-authors with Yang are UC Berkeley graduate student Hao Zhang and former postdoctoral fellow Hao Liu, now at Donghua University in Shanghai, China.

Here’s a link to and a citation for the paper,

Bacteria photosensitized by intracellular gold nanoclusters for solar fuel production by Hao Zhang, Hao Liu, Zhiquan Tian, Dylan Lu, Yi Yu, Stefano Cestellos-Blanco, Kelsey K. Sakimoto, & Peidong Yang. Nature Nanotechnologyvolume 13, pages900–905 (2018). DOI: https://doi.org/10.1038/s41565-018-0267-z Published: 01 October 2018

This paper is behind a paywall.

For lovers of animation, the folks at UC Berkeley have produced this piece about the ‘gold-loving’ bacterium,

Not the same old gold: there’s a brand new phase

A Dec. 7, 2015 news item on ScienceDaily announces a new phase for gold has been identified,

A new and stable phase of gold with different physical and optical properties from those of conventional gold has been synthesized by Agency for Science, Technology and Research (A*STAR) researchers [1], Singapore, and promises to be useful for a wide range of applications, including plasmonics and catalysis.

Many materials exist in a variety of crystal structures, known as phases or polymorphs. These different phases have the same chemical composition but different physical structures, which give rise to different properties. For example, two well-known polymorphs of carbon, graphite and diamond, arranged differently, have radically different physical properties, despite being the same element.

Gold has been used for many purposes throughout history, including jewelry, electronics and catalysis. Until now it has always been produced in one phase ― a face-centered cubic structure in which atoms are located at the corners and the center of each face of the constituent cubes.

Now, Lin Wu and colleagues at the Institute of the A*STAR Institute of High Performance Computing have modeled the optical and plasmonic properties of nanoscale ribbons of a new phase of gold — the 4H hexagonal phase (…) — produced and characterized by collaborators at other institutes in Singapore, China and the USA. The team synthesized nanoribbons of the new phase by simply heating the gold (III) chloride hydrate (HAuCl4) with a mixture of three organic solvents and then centrifuging and washing the product. This gave a high yield of about 60 per cent.

Here’s an image supplied by the researchers,

The atomic structure of the new phase of gold synthesized by A*STAR researchers. Reproduced from Ref. 1 and licensed under CC BY 4.0 © 2015 Z. Fan et al.

The atomic structure of the new phase of gold synthesized by A*STAR researchers. Reproduced from Ref. 1 and licensed under CC BY 4.0 © 2015 Z. Fan et al.

A Dec. 2, 2015 A*STAR news release, which originated the news item, provides more details,

The researchers also produced 4H hexagonal phases of the precious metals silver, platinum and palladium by growing them on top of the gold 4H hexagonal phase.

The cubic phase looks identical when viewed front on, from one side or from above. In contrast, the new 4H hexagonal phase lacks this cubic symmetry and hence varies more with direction — a property known as anisotropy. This lower symmetry gives it more directionally varying optical properties, which may make it useful for plasmonic applications. “Our finding is not only is of fundamental interest, but it also provides a new avenue for unconventional applications of plasmonic devices,” says Wu.

The team is keen to explore the potential of their new phase. “In the future, we hope to leverage the unconventional anisotropic properties of the new gold phase and design new devices with excellent performances not achievable with conventional face-centered-cubic gold,” says Wu. The synthesis method also gives rise to the potential for new strategies for controlling the crystalline phase of nanomaterials made from the noble metals.

Here’s a link to and a citation for the paper,

Stabilization of 4H hexagonal phase in gold nanoribbons by Zhanxi Fan, Michel Bosman, Xiao Huang, Ding Huang, Yi Yu, Khuong P. Ong, Yuriy A. Akimov, Lin Wu, Bing Li, Jumiati Wu, Ying Huang, Qing Liu, Ching Eng Png, Chee Lip Gan, Peidong Yang & Hua Zhang. Nature Communications 6, Article number: 7684 doi:10.1038/ncomms8684 Published 28 July 2015

This is an open access paper.