Embodiments of the invention concern copolymers and nanoparticles for use as delivery agents for one or more agents for therapy for a medical condition of humans and animals. Some of embodiments of the invention provide new reagents for biomedical research in cell culture, animal models and plants, for example. The copolymers comprise PLGA and PEI and, in some embodiments, also comprise 1-(3-aminopropyl)-4-methylpiperazine (APMP), Fc binding peptide and/or antibody. In certain embodiments, APMP-PLGA-PEI, Fc binding peptide/antibody-PLGA-PEI or Fc binding peptide/antibody-AP-MP-PLGA-PEI nanoparticles comprising one or more therapeutic agents are delivered to an individual in need thereof or used for biomedical research in cell cultures, animal models and plants.