Multifaceted core-shell nanoparticles: superparamagnetism and biocompatibilityElectronic supplementary information (ESI) available: XPS of pristine Ni nanoparticles (Fig. S1), particle size distribution of Ni nanoparticles (Fig. S2), the magnified HRTEM image of NicoreAgshell (Fig. S3), EDX spectra of NicoreAgshell nanoparticles (Fig. S4), zeta potential measurement data for Ni (Fig. S5), zeta potential measurement data for Trp modified Ni (Fig. S6), the XRD pattern of NicoreAushell nanoparticle

Ni core Ag shell nanoparticles were synthesized by redox transmetallation reaction. Reduction potential match was encouraging to attempt the synthesis of the Ni core Au shell system too. However, it could be achieved only after an effective surface modification on the Ni-core. Thorough characterization (UV-Vis spectroscopy, fluorescence spectroscopy, XRD, XPS, FTIR, TEM, and EDX) proved the necessity of surface modification and the success of synthesis of both types of core-shell structures. The chemical composition and topography were determined using STEM-HAADF analysis and EFTEM imaging. Fourier transform infrared (FTIR) spectroscopy confirmed the surface modification of Ni nanoparticles and the interactions involved between the ligands and metals (in the core and/or the shell) at various steps of the synthetic process. Even after the formation of the noble metal shell, the magnetic core was found to retain its superparamagnetic nature. In addition, the Au-shell protected the core from aerial oxidation and decreased toxicity as compared to pristine Ni nanoparticles as observed by MTT assay on normal cells (PBMCs). A facile method for the synthesis of Ni core Ag shell and Ni core Au shell nanoparticles with suitable surface modification for the latter has been demonstrated with potential applications.