Cooperative dynamics of DNA grafted magnetic nanoparticles optimize magnetic biosensing and coupling to DNA origami

Magnetic nanoparticles (MNPs) enable unique capabilities for biosensing and actuation via coupling to DNA origami, yet how DNA grafting density affects their dynamics and accessibility remains poorly understood. Here, we demonstrate functionalization of MNPs with single-stranded DNA (ssDNA) via click chemistry conjugation with tunable grafting density. Several complementary methods show that particle translational and rotational dynamics exhibit a sigmoidal dependence on ssDNA grafting density. At low densities ssDNA strands are coiled and cause small changes to particle dynamics, while at high densities they form polymer brushes that cooperatively change particle dynamics. Intermediate ssDNA densities show the highest magnetic biosensing sensitivity for detection of target nucleic acids. Finally, we demonstrate that MNPs with high grafting densities are required to efficiently couple them to DNA origami. These results together establish ssDNA grafting density as a critical parameter for functionalization of MNPs for use in a broad range of applications. ### Competing Interest Statement The authors have declared no competing interest.