Self-assembly of gold nanoparticles in protein crystal

► Gold nanoparticles are assembled three-dimensionally into a lysozyme crystal. ► The crystals were formed by incubating a crystallization solution containing lysozyme and gold nanoparticles at 20 °C. ► The gold nanoparticles were assembled in {1 0 1} sectors of the tetragonal lysozyme crystal. ► The gold nanoparticles are assembled into the crystal by an electrostatic interaction between the gold nanoparticles and the lysozyme on the crystal surface.