Graft copolymer polyelectrolyte complexes are disclosed for the efficient delivery of anionic, cationic or polyelectrolyte therapeutic agents into biological cells, and for maintaining the biological activity of these molecules while in serum and other aqueous environments are provided. Such complexes comprise (1) an anionic graft copolymer containing an anionic polymer backbone, with pendent carboxylic acid groups and pendant chains containing amphipathic or hydrophilic polymers covalently bonded to a portion of the pendant carboxylic acid groups, (2) one or more anionic, cationic or polyelectrolyte therapeutic agents, and (3) optionally a liposome optionally containing an additional therapeutic agent. Also disclosed are functional nanoparticles containing the complexes.