Abstract: A core-first method is provided for making a core-shell nanoparticle that includes the following steps: adding to a solvent, a mono-vinyl monomer cross-linked with a cross-linking agent to form the core of the nanoparticle, the core having an average diameter of 5 nanometers to about 10,000 nanometers, and the core having polymer chains with living ends; adding a charge agent comprising a fixed formal charge group onto the living ends of the core to form the shell of the nanoparticle; controlling the charge of the nanoparticle based on the type of charge agent, the quantity of the charge agent, or both the type of charge agent and the quantity of the charge agent. A core-shell nanoparticle is also provided.