Optical nanoantennas (ONAs) convert freely propagating optical radiation into localized fields and vice-versa, enabling precise manipulation of light–matter interactions and giving rise to phenomena such as fluorescence enhancement, ultrafast emission, and controllable emission patterns, just to name a few. High-index dielectric (HID) materials, such as silicon, are particularly attractive for use in ONAs due to their low ohmic losses and overlapping electric and magnetic modes of comparable strength in the visible range. However, positioning and orienting HID particles with sufficient precision to unlock their potential as low-loss nanoantennas has been difficult, primarily due to their unique surface chemistry. To address this challenge, this thesis employs DNA origami, a bottom-up self-assembly technique, to position both silicon nanoparticles and fluorophores in pre-determined positions with nanometer precision. To achieve this, a new technique is developed for the dense functionalization of silicon nanoparticles with DNA, which enables their assembly into DNA origami-mediated silicon antennas. It is demonstrated that the angular responses of these HID nanoantennas can be tuned to give control over emission direction and wavelength routing, and the low-loss behavior of these nanoantennas is demonstrated by studying the interactions of single emitters with silicon nanoparticles at defined distances. By enhancing our ability to control how light interacts with HID nanoantennas, the results presented herein offer exciting possibilities for the use of optical nanoantennas beyond the limitations of metallic nanoparticles.