DNA nanotechnology has developed into a state where the design and assembly of complex nanoscale structures is fast, reliable, cost effective, and accessible to nonexperts. Nanometer-precise positioning of organic (e.g., dyes and biomolecules) and inorganic (e.g., metal nanoparticles and colloidal quantum dots) components on DNA nanostructures is straightforward and modular. In this article, we identify the opportunities and challenges that DNA-assembled devices and materials face for optical antennas, metamaterials, and sensing applications. With the ability to arrange hybrid components in defined geometries, plasmonic effects will, for example, amplify molecular recognition transduction such that single-molecule events will be measureable with simple devices. On a larger scale, DNA nanotechnology has the potential to break the symmetry of common self-assembled functional materials, creating predefined optical properties such as refractive-index tuning and topological insulation.