An international team of researchers has established a way for aligning gold nanorods using magnetic fields while retaining the gold nanorods’ underlying optical characteristics.
Electron micrograph of gold nanorods overcoated with iron oxide nanoparticles and aligned in a magnetic field. Image Credit: Mehedi H. Rizvi.
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.
Joe Tracy, Study Corresponding Author and Professor, Materials Science and Engineering, North Carolina State University
The dimensions of the gold nanorods can be engineered to adjust the wavelengths of light absorbed and scattered. By magnetically controlling their orientation, the nanorods can be further controlled and modulated in terms of the wavelengths they respond to.
Tracy added, “In other words, if you can control the alignment of gold nanorods, you have greater control over their optical properties. And using magnetic fields to control that alignment means that you can control the alignment without actually touching the nanorods.”
The researchers utilized their approach to form distinct solutions of gold nanorods and iron oxide nanoparticles. The assembly of the iron oxide nanoparticles onto the surface of the gold nanorods is accelerated by mixing the solutions. A low-strength magnetic field can then be used to regulate the resultant “coated” nanorods.
“We have characterized both what is happening during this process and how well it works. We have demonstrated that we can bring the nanorods into alignment and that the process does not adversely affect the optical properties of the gold nanorods,” stated Tracy.
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.
Mehedi Rizvi, Study First Author and PhD Student, North Carolina State University
Rizvi further stated, “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,” added Tracy.
The study is available online in the journal Advanced Materials.
William Crumpler, a former NC State undergraduate, Ruosong Wang and Jonas Schubert of the Institute for Physical Chemistry and Polymer Physics, Christian Rossner and Andreas Fery of the Institute for Physical Chemistry and Polymer Physics and Technische Universität Dresden, and Amy Oldenburg of the University of North Carolina, Chapel Hill all contributed to the paper.
The work was funded by the National Science Foundation under grants CMMI-1763025 and CBET-1803830, as well as the Alexander von Humboldt Foundation, the Deutsche Forschungsgemeinschaft (the German Research Foundation), the Fonds der Chemischen Industrie, and the China Scholarship Council.
Journal Reference:
Rizvi, M. H., et al. (2022) Magnetic Alignment for Plasmonic Control of Gold Nanorods Coated with Iron Oxide Nanoparticles. Advanced Materials. doi:10.1002/adma.202203366.