Synthesis of Multibranched Gold Nanoechinus Using a Gemini Cationic Surfactant and Its Application for Surface Enhanced Raman Scattering

High-yield multibranched Au nanoechinus possessing lengthy and dense branched nanorods on the surface were synthesized using a seed-mediated surfactant-directed approach in the presence of gemini cationic surfactant N,N,N′N′-tetramethyl-N,N′-ditetradecylethane-1,2-diaminium bromide (C<sub>14</sub>C<sub>2</sub>C<sub>14</sub>Br<sub>2</sub>), HAuCl<sub>4</sub>, AgNO<sub>3</sub>, and ascorbic acid. C<sub>14</sub>C<sub>2</sub>C<sub>14</sub>Br<sub>2</sub> surfactant provides a versatile template in designing the unique morphology of Au nanoechinus with the assistance of AgNO<sub>3</sub>. UV–vis spectroscopic analysis proves that Au nanoechinus possess a unique intense broad localized surface plasmon resonance (LSPR) peak, which extends from 400 to 1700 nm in the NIR region making a highly potential platform for biomedical applications. Systematic time-dependent TEM, UV–vis–NIR, and XRD analysis were performed to monitor the morphological evolution of multibranched Au nanoechinus. It was found that the surface of branched nanorods of Au NE preferentially grew along (111) crystal planes. Furthermore, as-synthesized Au nanoechinus shows excellent SERS enhancement ability for dopamine inside HeLa cells.