Pt cores: 5 nm and 20 nm Pt nanoparticles were synthesized using the Bigall et al. method . For 5 nm Pt nanoparticles, 18 mL of chloroplatinic acid hexahydrate (0.2%) was added to 232 mL of DI water at 100 o C. After 1 min, 5.5 mL of a solution containing sodium citrate (0.1%) and citric acid (0.05%) was added. Then 2.75 mL of NaBH4 (0.08%), sodium citrate (1%), and citric acid (0.05%) was injected and the reaction was allowed to proceed for 10 min before cooling. The same solution was used without cleaning for shell coatings. For 20 nm Pt nanoparticles, 1 mL of 5 nm Pt nanoparticles were dispersed in 29 mL of DI water. 0.045 mL of chloroplatinic acid solution (0.4 M) was added to the solution. Then, 0.5 mL of sodium citrate (1%) and Lascorbic acid (1.25%) was added. Temperature was increased to the boiling point while stirring. The nanoparticle solution was kept at 100 o C for 30 min, after which the nanoparticles were centrifuged at 10,000 rpm and cleaned with water before redispersion in water.