North Carolina State University researchers have shown that the "bulkiness" of molecules commonly used in the creation of gold nanoparticles actually dictates the size of the nanoparticles with larger so-called ligands resulting in smaller nanoparticles. The research team also found that each type of ligand produces nanoparticles in a particular array of discrete sizes.
"This work advances our understanding of nanoparticle formation, and gives us a new tool for controlling the size and characteristics of gold nanoparticles," says Dr. Joseph Tracy, an assistant professor of materials science and engineering at NC State and co-author of a paper describing the research. Gold nanoparticles are used in industrial chemical processes, as well as medical and electronics applications.
When creating gold nanoparticles, scientists often use organic molecules called ligands to facilitate the process. The ligands effectively bring gold atoms together in a solution to create the nanoparticles. In the process, ligands essentially line up side by side and surround the nanoparticles in all three dimensions.
The researchers wanted to see whether the bulkiness of the ligands affected nanoparticle size, and opted to assess three types of thiol ligands a family of ligands commonly used to synthesize gold nanoparticles. Specifically, the molecules bound to the gold nanoparticles are linear hexanethiolate (-SC6), cyclohexanethiolate (-SCy) and 1-adamantanethiolate (-SAd). Each of these ligands has a bulkier configuration than the last.
For example, picture each ligand as a slice of pie, with a gold atom attached to the pointed end. -SC6 looks like a very narrow slice of pie. -SCy is slightly larger, and -SAd is the largest of the three with the "crust" end of the pie wedge far wider than the pointed end.
The researchers found that the bulkiness of the ligands determined the size of the nanoparticles. Because fewer -SAd and -SCy ligands
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North Carolina State University