Compositions and methods are provided that are useful for the delivery oftherapeutic agents, including nucleic acids. The compositions comprises a non-covalent association complex of: a) a positively-charged backbone and b) atleast two members selected from: I) a first negatively-charged backbone havinga plurality of attached imaging molecules； ü) a second negatively-chargedbackbone having a plurality of attached targetting agents； üi) at least onemember selected from RNA, DNA, ribozymes, modified oligonucleotides and cDNAendcoding a selected transgene； iv) DNA encoding at lest one persistencefactor； and v) a third negatively-charged backbone having a plurality ofattached biological agents； wherein the association complex carries a netpositive charge and at least one of the two members from group b) is selectedfrom I) iii) or v).
