(359f) Seed-Mediated Growth of Au Nanorods with Controllable Sizes

The size and shape controlled synthesis of nanostructures is of contemporary interest because their properties at this scale are highly size and shape dependent. Gold nanorods exhibit transverse and longitudinal surface plasmon resonances that correspond to electron oscillations perpendicular and parallel to the rod length direction, respectively. The longitudinal surface plasmon wavelengths (LSPWs) of Au nanorods are desired in the spectral range of 650-900 nm. Light irradiation in this region can penetrate deeper in tissues and cause less photodamage than UV-visible irradiation. As such, development of methodology to tailor both scattering and absorption of Au nanorods with different LSPWs is of ultimate importance for practical application in biomedical imaging and therapeutic systems.

In this presentation, we report the seed-mediated growth of Au nanorods with controllable size by synthesizing Au seeds of designed size through careful control of kinetics. The reduction of the Au salt by NaBH₄ in the presence of cetyltrimethyl ammonium bromide (CTAB) within the aqueous phase was demonstrated to be a slow reaction. This allows for an ability to manipulate Au nanoparticle sizes through control of the reaction/growth duration (2, 8, 24, 48, 72, 146 hours were selected in this work). These differently sized Au nanoparticles were subsequently used as seeds for secondary growth where the addition of Au salt, AgNO₃, and weak reducing agent, ascorbic acid was required. Smaller Au nanoparticle seeds obtained from short reduction/growth times resulted in Au nanorods with both longer LSPWs and higher aspect ratio, and the larger Au nanoparticle seeds, those obtained from longer reduction/growth times, resulted in Au nanorods with shorter LSPW and lower aspect ratio, illustrating the ability to manipulate size and aspect ratio of the Au nanorods through careful control of the original Au seeds. Moreover, the effect of Au salt, AgNO₃, and ascorbic acid concentration used during the seed mediated growth process, as well as the growth temperature, on the LSPWs and aspect ratio of the resultant Au nanorods were systematically investigated and will be discussed in this presentation.