Dynamic light scattering determinations for Citrate-CPNP, Anti-CD71-Avidin-CPNPs (Anti-CD71-Av-CPNP), Human Holotransferrin-Avidin-CPNPs (Tf-Av-CPNP), Pentagastrin-Avidin-CPNPs (PG-Av-CPNP), maleimidePEG-CPNPs (PEG-CPNP), and Gastrin 10-maleimidePEG-CPNPs (Gastrin-10-PEG-CPNP). All dynamic light scattering determinations are the mean of three independent experiments. Inset shows a typical TEM micrograph of Citrate-CPNPs.