Au nanoparticles have a plasmonic resonance which is useful for applications in biomedicine and photonics . Figure shows that the plasmon resonance of citrate-Au nanoparticles has a peak around ~530 nm. The plasmon resonance of the Au core nanoparticle is retained after coating with the NiB shell. The plasmon peak width increases after the additional of the shell coating and the peak intensity drops with increasing thickness of the NiB shell, but the energy of the peak does not shift (Figure ).