MG shell coating: Similar procedures were used to coat Au and Pt core particles with NiB or CoB. Here, we provide details for forming a 30 nm NiB shell on citrate-Au nanoparticles. 100 mL of DI water with 0.01 M sodium dodecyl sulfate and 0.001 M nickel nitrate hexahydrate (or cobalt nitrate hexahydrate for CoB shell coatings) was first prepared. Citrate-Au nanoparticle solution was added and then stirred rapidly before 0.02 g of NaBH4 was dropped directly into the solution. After waiting for one minute for the solution to turn black, 1 mL of methanol with 0.01 M oleic acid was rapidly injected into the solution. The solution was left unstirred for one hour before centrifugation, cleaning, and dispersion in water. To make coatings of different thicknesses, the Au NP solution amount was varied. This synthesis could be scaled up from 10 mL to 200 mL batches by maintaining the same Au core concentration. For long term storage of particles, an additional 100 µL of methanol with 0.01 M oleic acid was added after cleaning. Samples are named as citrate-Au@NiB which indicates that citrate-Au nanoparticles were coated with NiB shell.