Au cores: Au nanoparticle cores were synthesized using two established methods . Citrate stabilized Au nanoparticles (citrate-Au) were synthesized using the Bastús et al. method . Briefly, 2.2 mM sodium citrate was dissolved in 150 mL deionized (DI) water and heated under vigorous stirring for 15 min with a condenser. After a temperature of 100 o C was reached, 1 mL of HAuCl4 (25mM) was added to the solution. Immediately after this, the reaction was brought to 90 o C and 1 mL of sodium citrate (60 mM) and 1 mL of HAuCl4 solution (25 mM) were injected one after the other with 2 minutes between the injections. This process was repeated twice to make nanoparticles of the appropriate size. The nanoparticles were precipitated at 10,000 rpm centrifugation and then washed twice with water before dispersion in water.