Gold nanorods with an aspect ratio (A.R.) of 3 were prepared
in the presence of CTAB following a seed-mediated approach as
previously reported [3,12]. Briefly, to a 2.5 104 M chloroauric
acid solution containing 0.1 M CTAB was added 600 lL of 0.01 M
ice-cold sodium borohydride under vigorous stirring for 10 min
resulting in 1.5 nm spherical ‘‘seed” particles. After a minimum
of 60 min, 12 lL of these seed particles were added to a growth
solution containing 9.5 mL of 0.1 M CTAB, 60 lL of 0.01 M silver
nitrate, 5 104 M chloroauric acid and 55 lL of 0.1 M ascorbic
acid. Rod growth was allowed to proceed overnight and nanorod
solutions were purified by centrifugation at 10,000 rpm for
30 min. All nanorods were resuspended in 10 mL deionized water.
Supernatants containing unreacted CTAB, Au1+, Ag1+/Ag0
, and
ascorbic acid were removed and saved for subsequent re-seeding
events. For each seeding event 5, 10 mL samples were prepared.