1 © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com Synthesis of Fivefold Stellate Polyhedral Gold Nanoparticles with {110}-Facets via a Seed-Mediated Growth Method Lin Jiang, Yuxin Tang, Chihao Liow, Jinsong Wu, Yinghui Sun, Yueyue Jiang, Zhili Dong, Shuzhou Li, Vinayak P. Dravid, and Xiaodong Chen* The controlled synthesis of noble metal nanoparticles on their shape and size is drawing much attention because the ability to tailor particle architecture enables one to ration- ally design their optical, electrical, catalytic, and magnetic properties. [1–8] The seed-mediated growth method, separating the nucleation and growth stages of nanoparticles, [9–15] has proven to be especially versatile for preparing anisotropic Au nanoparticles of various shapes from simple rods to poly- hedral structures with the low-index crystallographic faces of {111}, {100} and {110}. [16–24] This method has a variety of factors, including metal precursors, reducing agents, additives, and impurities, which can be used to tune the particle mor- phology. [1,2] It is noted that the stellate polyhedral structures with the sharp corners and edges are attracting tremendous interest because of their significantly enhanced performance for catalytic, plasmonic, energy conversion, and spectroscopic applications. [25–27] Although a few Au stellate polyhedral structures with {111} have been recently reported, [28–31] the growth of stellate polyhedron with {110} facets especially with systematic shape evolution still presents significant syn- thetic challenges. It is because of the higher surface energy of {110} facets compared with that of the other low-index facets ({111} and {100}), which in turn could endow their high activity and facilitate their potential application as highly efficient catalysts. [32–34] As a result, most syntheses for {110}- faceted nanoparticles require high temperature or compli- cated procedures (such as utilizing surfactant or capping agent to stabilize the facets), [20,22,35] which have the limitation for the further applications. Herein, we describe a surfactantless way to yield a novel class of {110}-faceted fivefold stellate polyhedral Au nanoparticles (FSPAuNPs) based on the seed- mediated growth method ( Figure 1A). Importantly, the dia- meter of this class of novel nanoparticles can be adjusted from tens to thousands of nanometers by simply varying the con- centration of seeds in the growth solution. Such FSPAuNPs with facile replaced {110}-faceted surface will provide the promising application in plasmonics and catalysis. In a typical experiment, a solution of 13 nm Au seeds (Figure 1B) was prepared by citrate reduction of HAuCl 4 . [36] Then, 30 μL of NH 2 OH·HCl solution (200 mM) and 20 μL Au seed solution (800 pM) were added into 4 mL HAuCl 4 solution (0.25 mM, pH = 5.8) at 25 °C, respectively. In this case, the final concentration of Au seeds is 4 pM, and the con- centration of NH 2 OH·HCl is 1.5 mM, which is much higher than the conventional concentration of 0.3 mM reported in the literature. [37] With mild shaking, the color of the solution changed from pale pink to yellow gold (Figure 1B,C) within 2 min and the as-grown nanoparticles were purified by cen- trifugation for further characterization. Scanning electron microscope (SEM) measurement (Figure 1C) indicates the formation of FSPAuNPs with a yield of more than 85% and an average diameter (D F ) of 460 ± 15 nm. Furthermore, atomic force microscope (AFM) measurement was used to characterize the 3D fivefold sym- metric structure of such nanoparticles. The typical top-view height image of AFM measurement (Figure 1D) shows that FSPAuNPs are composed of multiple layers of pentacle struc- tures. The thickness of the first layer pentacle structure (white color part in Figure 1D) is about 105 nm, and the diameter is about 260 nm. The thickness of the second layer (yellow color part in Figure 1D) is about 65 nm with the diameter of 460 nm, which is larger than that of the first layer. The third layer (green color in Figure 1D) has similar size, shape, and thickness compared with the second layer, but a 36 ° rotation. The thickness of the fourth layer is deducted to be around 105 nm from the height profile measurement (the total height of FSPAuNPs is around 340 nm), which is similar to the first layer. Moreover, the morphology of the fourth layer is also expected to be same with the first one since only pentacle structure was observed from the particle inspected ( >5000). Therefore, we can conclude that the obtained FSPAuNPs are composed of four layers of fivefold pentacle (Figure 1E). DOI: 10.1002/smll.201202561 Gold Nanostructures Dr. L. Jiang, Y. Tang, C. Liow, Dr. Y. Sun, Y. Jiang, Prof. Z. Dong, Prof. S. Li, Prof. X. Chen School of Materials Science and Engineering Nanyang Technological University 50 Nanyang Avenue, Singapore 639798, Singapore Website: http://www.ntu.edu.sg/home/chenxd/ E-mail: chenxd@ntu.edu.sg Dr. J. Wu, Prof. V. P. Dravid Department of Materials Science and Engineering Northwestern University Evanston, Illinois, 60208, USA small 2012, DOI: 10.1002/smll.201202561