Influence of stirring in the synthesis of gold nanorods

Gold nanorods have been prepared by the seed-mediated growth method, in order to find the effect of stirring during the synthesis to the final shape and optical properties. The presence or absence of stirring during each step of the preparation procedure was considered a parameter to control in order to adjust the optical absorption associated with the surface plasmon resonance of the nanorods. Results show that the longitudinal surface plasmon resonance band shifts to larger wavelengths in the absence of stirring of the growth solution. Width and intensity of the absorption band associated with the longitudinal surface plasmon is reduced upon stirring during the synthesis. On the contrary, the position of the transversal surface plasmon resonance band scarcely depends upon stirring. Theoretical calculations performed using the Gans model are coherent with experimental obtained results, showing that as the aspect ratio increases, longitudinal plasmons absorption shifts toward larger wavelengths and increases both intensity and bandwidth.

Research highlights
► Control of nanoparticles shape during synthesis constitutes a preparative challenge.
► We present here a method to tune gold nanorods aspect ratio.
► Control of stirring during the nanorods synthesis is a key factor.
► Stirring modifies the aspect ratio and the optical properties of gold nanorods.