Gold nanoparticles grow from buckyball seeds

Chemists at Rice University have confirmed that tiny gold ‘seed’ particles, a key ingredient in one of the most common nanoparticle recipes, are one and the same as gold buckyballs, 32-atom spherical molecules that are cousins of the carbon buckyballs discovered at Rice in 1985.

Carbon buckyballs are hollow 60-atom molecules that were co-discovered and named by the late Rice chemist Richard Smalley. He dubbed them ‘buckminsterfullerenes’ because their atomic structure reminded him of architect Buckminster Fuller’s geodesic domes, and the ‘fullerene’ family has grown to include dozens of hollow molecules.

In 2019, Rice chemists Matthew Jones and Liang Qiao uncovered evidence that golden fullerenes are the gold ‘seed’ particles chemists have long used to make gold nanoparticles. This finding came just a few months after the first reported synthesis of gold buckyballs, and it revealed that chemists had unknowingly been using the golden molecules for decades.

“What we're talking about is, arguably, the most ubiquitous method for generating any nanomaterial,” Jones said. “And the reason is that it’s just so incredibly simple. You don’t need specialized equipment for this. High school students can do it.”

Jones, Qiao and colleagues from Rice, Johns Hopkins University, George Mason University and Princeton University spent years compiling evidence to verify the discovery and recently reported their results in a paper in Nature Communications.

Jones, an assistant professor in chemistry and materials science and nanoengineering at Rice, said the knowledge that gold nanoparticles are synthesized from molecules could help chemists uncover the mechanisms of those syntheses. “That’s the big picture for why this work is important,” he said.

Researchers discovered in the early 2000s how to use gold seed particles in chemical syntheses that produced many shapes of gold nanoparticles, including rods, cubes and pyramids.

“It's really appealing to be able to control particle shape, because that changes many of the properties,” Jones said. “This is the synthesis that almost everyone uses. It’s been used for 20 years, and for that whole period of time, these seeds were simply described as ‘particles’.”

Jones and Qiao, a former postdoctoral researcher in Jones’ lab, weren’t looking for gold-32 in 2019, but they noticed it in mass spectrometry readings. The original discovery of carbon-60 buckyballs happened in a similar way.

Confirming that the widely used seeds were gold-32 molecules rather than nanoparticles took years of effort, involving state-of-the-art imaging by Yimo Han’s research group at Rice and detailed theoretical analyses by the groups of both Rigoberto Hernandez at Johns Hopkins and Andre Clayborne at George Mason.

According to Jones, the distinction between nanoparticle and molecule is important and a key to understanding the study’s potential impact. “Nanoparticles are typically similar in size and shape, but they are not identical,” he said. “If I make a batch of 7nm spherical gold nanoparticles, some of them will have exactly 10,000 atoms, but others might have 10,023 or 9092.

“Molecules, on the other hand, are perfect. I can write out a formula for a molecule. I can draw a molecule. And if I make a solution of molecules, they are all exactly the same in the number, type and connectivity of their atoms.”

Jones added that nanoscientists have learned how to synthesize many useful nanoparticles, but progress has often come via trial and error because “there is virtually no mechanistic understanding” of their synthesis.

“The problem here is pretty straightforward,” he said. “It’s like saying, ‘I want you to bake me a cake, and I'm gonna give you a bunch of white powders, but I'm not going to tell you what they are’. Even if you have a recipe, if you don't know what the starting materials are, it’s a nightmare to figure out what ingredients are doing what.

“I want nanoscience to be like organic chemistry, where you can make essentially whatever you want, with whatever properties you want.”

He said that organic chemists have exquisite control over matter “because chemists before them did incredibly detailed mechanistic work to understand all of the precise ways in which those reactions operate. We are very, very far from that in nanoscience, but the only way we’ll ever get there is by doing work like this and understanding, mechanistically, what we’re starting with and how things form. That’s the ultimate goal.”

This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.