Provided herein is a process for production of a metal nanoparticle, the process comprising providing a first solution containing a protein nanocage complex comprising a hydrophobic metal core and an ion-transport mechanism, providing a second solution containing a preselected anionic agent, combining the first and second solutions into a third combined solution, and applying an external method to the third combined solution to manipulate the metal cores redox state, in which reduction of the metal core causes the preselected anionic agent to be imported and incorporated into the metal core. Also provided herein is a composition from the process and a method of use.
