The research team of Professor Seung-woo Lee become the first to confirm magnetic plasmon resonance in the visible light region through a DNA self-assembled nanostructure.

▲ Professor Seung-woo Lee, KU-KIST Graduate School of Convergence Science and Technology (left), Ji-Hyeok Huh (right)

Seung-woo Lee, professor at KU-KIST Convergence Graduate School of Korea University, and his team have implemented a meta nanostructure that can generate and guide magnetic plasmon resonance as light propagates along an optical fiber, using molecular DNA-origami technology.

Metamaterials, which are widely known as negative refractive index materials and commonly known as transparency cloaks by the public, can be applied to wide-ranging industries including telecommunication, energy, electromagnetic pulses, and defense through the research and development of artificial materials featuring physical properties not present in nature. The field has been actively researched over the past 20 years and, along with the development of advanced ICT technologies, such as 5G and Internet of Things (IoT), has become a hot topic because of increasing demand for cutting-edge parts as the 4th Industrial Revolution draws upon us.

The biggest obstacle to the implementation of metamaterials is the difficulty of inducing a magnetic field response with the electromagnetic waves entering a material. Most optical materials in the natural world react to electric fields but do not react well to the magnetic fields. Thus, for the field of metamaterials, artificially creating a structure that induces magnetic fields is an important issue. Although it is especially difficult to induce magnetic reactions closer to short wavelength regions, the research team of Korea University succeeded in implementing a nanostructure that induces a magnetic field in the short wavelength visible light region by simulating the structure of aromatic molecules such as benzene and naphthalene

In order to induce a magnetic reaction in the visible light region, a structure featuring metal nanoparticles spaced apart by a few nm is arranged in a ring-shaped circular structure. Because this is very difficult to implement using conventional etching processes, the team has overcome these limitations by using two key technologies.

First, a template of a hexagonal structure similar to the shape of an aromatic molecule was created using the latest molecular DNA-origami technology (the technique of carefully designing the nucleotide sequences of DNA molecules to self-assemble to form a desired nanostructure). The hexagonal DNA template has a handle with a single strand of DNA at each corner. If gold nanoparticles are coated with DNA featuring the exact opposite sequence to that of the handle and then mixed with the DNA template, they will selectively settle on the edges of the template (See Figure 1).

Second, to make the gap between the particles several nanometers wide, the gold nanoparticles at the edges of the DNA template were seeded to chemically grow silver. The advantage of this technique is that it is possible to adjust the gap between the particles according to the deposition time of the silver. Furthermore, the team were able to create more complex ring-shaped nanostructures and an overall network that guided the magnetic reactions (magnetic plasmon resonance) along the shape of the structure, similar to how current flows through a circuit. This was demonstrated both theoretically and experimentally (See Figure 2).

This is expected to be a foundational technology that can bring the wavelength region of the meta-material field into the visible light region. It opens the possibility of not only inducing magnetic plasmon resonance but also forming magnetic plasmon resonance in a circuit and controlling it. Recognized as a technology at the forefront of this effort, the results of the research team were published in one of the most prestigious academic journals in the field of materials engineering, Advanced Materials (Impact Factor: 21.950) on May 30th.

▲(Figure 1) DNA template-based nanoparticle growth process

▲(Figure 2) DNA template-based nanoparticle ring cluster composite