Bio‐inspired Synthesis of Protein‐Encapsulated CoPt Nanoparticles

Abstract The 24 subunit heat‐shock protein from Methanococcus jannaschii has been genetically altered to display a dodecapeptide on the interior surface that has a strong binding affinity to the L1₀ phase of CoPt (CP_Hsp). Reaction of Co^II and Pt^II salts at 65 °C under reducing conditions results in the formation of a stable CoPt mineral encapsulated within the protein cage. Metallic particles commensurate in size with the interior dimensions of the protein cage (6.5 ± 1.3 nm) have been imaged by transmission electron microscopy and are shown to be surrounded by the intact protein cage. Magnetic measurements performed on the encapsulated nanoparticles exhibit room‐temperature hysteresis on the order of 150 G (1 G = 10^–4 T) prior to annealing and 610 G after annealing at 650 °C.