Described herein are nucleic acid-peptide capsule complexes or nanoparticles comprising pre-formed peptide capsules and nucleic acids bound the exterior surface of the capsule, such that the wrap around the capsule membrane. The peptide capsules comprise bilayer membrane defining a liquid-receiving interior space and comprises a plurality of branched, amphipathic peptides. Method of making and using such complexes for delivering nucleic acids in vivo and in vitro are also described.