Integration of Lithography and DNA Mediated Self-Assembly for the Synthesis of Responsive Metamaterials
Dynamic materials have always held the interest of scientists because they change their properties in response to some stimulus. Being able to program the desired material properties before and after a stimulus is important to many sensing technologies. One interesting class of materials are termed ‘metamaterials’ because they interact with light in exotic ways that naturally occurring materials do not. These engineered materials are able to interact with light (or other frequencies of electromagnetic waves) in novel ways is due to the low symmetry arrangement of their components. In order to achieve the low symmetry arrangement, lithographic techniques are commonly used to fabricate these materials, because lithography can arrange nanoscale components in arbitrary patterns. However, most lithographed materials are static and do not react to external chemical stimuli. This dissertation lays out a novel approach to rationally assemble dynamic metamaterials by combining lithographic techniques with DNA mediated self-assembly, which imparts a responsive, organic component to the metamaterial.
Integrating DNA into a metamaterial allows for several advancements over lithographed-only metamaterials. First it allows for sub-nanometer control over the spacing of the constituent components. Second, DNA is responsive to a wide variety of stimuli—such as other DNA strands, salt, proteins, certain organic molecules, and temperature. Depending on the stimuli, one could then program a single metamaterial to respond in divergent ways to different chemical stimuli.
The model metamaterial examined here is a three nanorod system that exhibits a property known as electromagnetically induced transparency (EIT). Two rods are defined with lithography, and the third is assembled with DNA. This hybrid organic-inorganic structure behaves in accordance to plasmon hybridization theory and finite difference time domain (FDTD) simulations. Finally, external chemical stimuli, such as removing sodium cations or dehydrating the DNA, can cause the components to either decouple or couple more strongly, causing the EIT effect to either disappear or become enhanced, respectively. This assembly method allows for creating of dynamic metamaterials that can be predictably perturbed in order to change their desired optical properties.