The GNBs were synthesized via the seed-mediated growth approach, which has been used for various gold nanoparticles including GNRs . Briefly, a gold seed solution was first prepared via rapid reductions by NaBH4. Thereafter, the freshly prepared seed solution was added to the growth solution for crystal growth. The solution contained HAuCl4 as the gold source, AgNO3 as an additive to modulate the crystal growth, L-AA as a reductant, and surfactants. We observed that the surfactant solution containing benzyldimethyldodecylammonium chloride (BDAC) and hexadecyltrimethylammonium bromide (CTAB) in a 2:1 ratio, as well as 0.1 M total surfactant, was suitable for the highly efficient synthesis of GNBs. Similar compositions have been applied to the synthesis of rod-shaped GNRs, but this one has never been established because of its high sensitivity to the shape (vide infra). However, we observed that this unsteady condition was key to modulating asymmetry if adequately improved.