A novel approach to high-aspect ratio gold nanorods has been presented. The gold nanorods as long as (200±18.62) nm with aspect ratio of above 10 were prepared with optimizing the concentration of surfactant cetyltrimethylammonium bromide (CTAB) by seed-mediated growth method at 25 ℃. Mechanism for gold nanorods formation is discussed. It is shown that the aspect ratio and longitudinal surface plasmon resonance (SPR) can be correlated with the concentration of CTAB. Moreover, by simply enhancing the ion strength of the reaction solution, the as-prepared gold nanorods can be purified for the different electrostatic aggregation effects between gold nanorods and spherical nanoparticles. Shape change of gold nanorods is confirmed by transmission electron microscopy images (TEM) and scan electron microscopy (SEM).

Key words: gold nanorods, CTAB, ion strength, high aspect ratio