Provided are methods and compositions for nanoparticle delivery of payloads (e.g., nucleic acid and/or protein payloads) to cells. In some embodiments, a subject nanoparticle includes a core and a sheddable layer encapsulating the core, where the core includes (i) an anionic polymer composition； (ii) a cationic polymer composition； (iii) a cationic polypeptide composition； and (iv) a nucleic acid and/or protein payload； and where: (a) the anionic polymer composition includes polymers of D-isomers of an anionic amino acid and polymers of L-isomers of an anionic amino acid, and/or (b) the cationic polymer composition comprises polymers of D-isomers of a cationic amino acid and polymers of L-isomers of a cationic amino acid. In some cases, the polymers of D-isomers of an anionic and/or cationic amino acid are present at a ratio, relative to the polymers of L-isomers, in a range of from 10:1 to 1:10.
