Metallic nanoparticles and related methods of making and using the same are described herein. An aqueous synthesis method is used to create nanoparticle cores comprising alloys of two or more metals at varying metal:metal molar ratios. In some embodiments, the nanoparticle cores described herein form a homogeneous metal alloy. Alternatively, the nanoparticle cores form a heterogeneous metal alloy. The synthesis method can further comprise forming mixed metal oxide shells on the nanoparticle cores.