The new gene-editing tool CRISPR/Cas9 holds promise for new treatment of such genetic diseases as cystic fibrosis, muscular dystrophy and hemophilia. But to work well, it must be delivered across the cell membrane and into its nucleus, a process that can trigger cell defenses and ‘trap’ CRISPR/Cas9, reducing its treatment potential. Now, a research team has designed a delivery system using nanoparticles to assist CRISPR/Cas9 across the membrane and avoid entrapment by cellular machinery.