Bio-inspired Synthesis of Protein-Encapsulated CoPt Nanoparticles

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 CoII and PtII 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. CoPt nanoparticles in protein cages have been synthesized (see Figure) by genetically altering the small heat‐shock protein cage from Methanococcus jannaschii to display a dodecapeptide, which has a strong affinity for the L10 phase of CoPt, on the interior surface. The CoPt particles are size constrained, and the cages are shown to be robust under a wide range of synthetic conditions.