Mixing silica-overcoated gold nanorods (left) and iron oxide nanoparticles (center) yields iron oxide-overcoated gold nanorods (right). Image: Brian Chapman.
Mixing silica-overcoated gold nanorods (left) and iron oxide nanoparticles (center) yields iron oxide-overcoated gold nanorods (right). Image: Brian Chapman.

Researchers from North Carolina State University (NC State) and Massachusetts Institute of Technology (MIT) have found a simple way to deposit magnetic iron oxide (magnetite) nanoparticles onto silica-coated gold nanorods. As they report in a paper in Chemistry of Materials, this will allow them to create multifunctional nanoparticles with useful magnetic and optical properties.

Gold nanorods have widespread potential applications because they have a surface plasmon resonance – meaning they can absorb and scatter light. By controlling the dimensions of the nanorods, specifically their aspect ratio (or length divided by diameter), the precise wavelength of the light that is absorbed and scattered can be controlled.

This characteristic makes gold nanorods attractive for use as catalysts and security materials, and for a host of biomedical applications, such as diagnostics, imaging and cancer therapy. Combining gold nanorods with magnetite nanoparticles means they can also be manipulated using a magnetic field, enhancing their potential usefulness for biomedical applications.

"The approach we outline in our new paper is simple, likely making it faster and less expensive than current techniques for creating these nanoparticles – on a small scale or a large one," says Joe Tracy, an associate professor of materials science and engineering at NC State and corresponding author of the paper.

The new technique uses an approach called heteroaggregation. Silica-coated gold nanorods are dispersed in ethanol, a polar solvent. The hydrogen atoms in ethanol are partially positively charged, while the oxygen atoms are partially negatively charged. The magnetite nanoparticles are dispersed in hexanes, a non-polar solvent, where the charges are not separated. When the two solutions are mixed, the magnetite nanoparticles bind to the gold nanorods – and the resulting magnetite-gold nanoparticles are then removed from the solvent using a simple centrifugation process.

"We are able to take pre-synthesized, silica-coated gold nanorods and iron oxide nanoparticles and then combine them," says Brian Chapman, a PhD student at NC State and lead author of the paper. "This is simpler than other techniques, which rely on either growing iron oxide nanoparticles on gold nanorods or using molecular cross-linkers to bind the iron to the silica coating of the nanorods."

"Our approach also results in highly uniform nanoparticles," Tracy adds. "And by incorporating ligands called PEG-catechols, the resulting nanoparticles can be dispersed in water. This makes them more useful for biomedical applications.

"These are interesting, and potentially very useful, multifunctional nanoparticles. And hopefully this work will facilitate the development of applications that capitalize on them."

This story is adapted from material from North Carolina State 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.