2026 Theses Doctoral

Realizing Pure Structural Colors via Inverse-Designed DNA Photonic Crystals

Yun, Alexia

Structural colors are vivid, iridescent colors that result from the interaction between light and the micro- and nanostructures of the materials. Challenges remain in realizing high-purity, non-spectral structural colors, which require building materials with periodicity of photonic length scales. In this dissertation, DNA-guided self-assembly is utilized to fabricate 3D, gold nanoparticle-based photonic crystals for harvesting spectral and non-spectral structural colors. DNA octahedron origami can connect via vertex bonds and self-assemble into crystal lattices. Through programming and building directional vertex bonds, gold nanoparticles can be positioned into periodic planes within the interior space of DNA origami. The optical performance of distributed Bragg reflectors is measured via purity of structural color and reflectivity efficiency. Purity is defined by FWHM of the Bragg peak and high saturation in the CIE space. Currently, its optical performance is limited by the self-assembly pathway of DNA origami host crystals, the sizes and layer density of gold nanoparticles, and the dimensions of distributed Bragg reflectors.

Average reflectivity is improved from 3% to 47% upon functionalization and accessing negative space, in addition to interior space, as gold nanoparticle positioning sites within the DNA origami host crystal (Chapter 2, 3, and 4). Negative space refers to the ordered, interstitial space that emerges among DNA origami after self-assembly, whereas interior space refer to the interior cavity of DNA origami. Through an inverse-designed approach, reflection-based structural colors spanning the visible spectrum, such as blue, green, orange, are realized by tuning the distance between gold nanoparticle planes (Chapter 5). Three multi-peak reflectance-based non-spectral structural colors, such as magenta and pink, are realized by building sub-micron sized features and using nanosized building blocks (Chapter 6). Silica coating is utilized for enhancing mechanical properties of soft matter-based distributed Bragg reflectors, shrinking lattice spacing for accessing blue-shifted structural colors, and accessing background effective index neff as a tuning knob for realizing differentiated structural colors (Chapter 7). This thesis shows that DNA-guided self-assembly is a promising platform for realizing inverse-designed photonic crystals with nanoscale precision, high-efficiency, and limited harsh-chemical waste.