Electron micrograph of gold nanorods overcoated with iron oxide nanoparticles and aligned in a magnetic field. When dispersed in water, gold nanorods overcoated with iron oxide nanoparticles align along the magnetic field pattern generated by arrays of permanent magnets, resulting in polarization-dependent absorption and scattering of light. The double-headed arrows indicate the polarization axis of a linear polarizer through which the sample was photographed. Image: Mehedi H. Rizvi.An international team of researchers has demonstrated a technique that allows them to align gold nanorods using magnetic fields, while preserving the underlying optical properties of the nanorods.
“Gold nanorods are of interest because they can absorb and scatter specific wavelengths of light, making them attractive for use in applications such as biomedical imaging, sensors and other technologies,” says Joe Tracy, a professor of materials science and engineering at North Carolina State University (NC State) and corresponding author of a paper on this work in Advanced Materials.
It is possible to tune the wavelengths of light absorbed and scattered by gold nanorods by engineering their dimensions. Magnetically controlling their orientation makes it possible to further control and modulate which wavelengths the nanorods respond to.
“In other words, if you can control the alignment of gold nanorods, you have greater control over their optical properties,” Tracy explains. “And using magnetic fields to control that alignment means that you can control the alignment without actually touching the nanorods.”
In their technique, the researchers synthesize separate solutions of gold nanorods and iron oxide nanoparticles. Mixing the solutions drives assembly of the iron oxide nanoparticles onto the surface of the gold nanorods. The resulting ‘coated’ nanorods can then be controlled using a low-strength magnetic field.
“We’ve characterized both what is happening during this process and how well it works,” Tracy says. “We’ve demonstrated that we can bring the nanorods into alignment and that the process does not adversely affect the optical properties of the gold nanorods.”
“In addition, to the best of our knowledge, these nanorods have the smallest aspect ratio of any elongated nanoparticle that has been ‘decorated’ with iron oxide nanoparticles and aligned using magnetic fields,” adds Mehedi Rizvi, a PhD student at NC State and first author of the paper.
“In order for this technique to work, we’ve had to optimize many aspects of the system, including the dimensions of the gold nanorods, the size of the iron oxide nanoparticles, and the relative concentrations of both nanorods and nanoparticles in solution.”
“We are currently in the process of exploring potential applications in imaging based on the multifunctional properties of magnetic-overcoated gold nanorods,” Tracy says.
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.