DOI: 10.1021/la901590s 11431 Langmuir 2009, 25(19), 11431–11435 Published on Web 06/17/2009 pubs.acs.org/Langmuir © 2009 American Chemical Society Gold Colloids with Unconventional Angled Shapes Ana Sanchez-Iglesias, †,‡ Marek Grzelczak, †,‡ Benito Rodrı´guez-Gonz alez, ‡ Ram on A.  Alvarez-Puebla, ‡ Luis M. Liz-Marz an,* ,‡ and Nicholas A. Kotov* ,† † Departments of Chemical Engineering, Materials Science and Engineering, Biomedical Engineering, University of Michigan, Ann Arbor, Michigan 48109, and ‡ Departamento de Quı´mica-Fı´sica and Unidad Asociada CSIC-Universidade de Vigo, 36310 Vigo, Spain Received May 4, 2009 We report the formation of porous gold nanoparticles with unusual, angled shapes (such as nanocheckmarks) through spontaneous transformation of tellurium sacrificial templates by gradual galvanic replacement. High-resolution electron microscopy studies of intermediate stages reveal interesting information regarding the replacement mechanism, which involves initial “gold island growth” at the edges, and gradual branching to engulf the entire particle templates, resulting in a highly porous structure. Additionally, the high porosity of these novel nanostructures with unusual shapes is demonstrated to provide very high enhancement of the Raman scattering signal from adsorbed molecules. Introduction Control over the overall shape of nanostructures is one of the most challenging and fundamental problems in today’s science. It is required by multiple technological areas, such as optics, catalysis, sensing, electronics, and, in fact, it is difficult to find advanced technologies that would not benefit from it. Noble metals hold special importance in nanoscale structures because of their unique optical as well as electronic properties, which have given rise to the emerging field of Plasmonics. 1 Gold and other noble metals have been produced in a wide variety of shapes: fairly spherical nanoparticles (NPs), 2,3 platonic solids, 4,5 nanorods, 6-8 and nano- plates, 9,10 among others. On occasion, even spikes can form on the surface of noble metal NPs; 11,12 however, the overall nano- colloids retain an approximately rotational symmetry. At the same time, nanocolloids from gold and other noble metals with de- creased symmetry, e.g., containing angled shapes, are of great interest because they are expected to display unique nonlinear optical properties, 13,14 plasmon localization, 15-17 shape-dependent biological properties, 18-20 and biosensing capabilities. 21-26 Re- cently, plasmonic NPs have been proposed as ideal candidates for the development of novel materials with anomalous dielectric properties (such as negative index of refraction materials, NIMs), currently known as metamaterials. 27-31 Angled NPs are particu- larly appealing for the design of NIMs in the ultraviolet-visible- near-infrared (UV-vis-NIR) wavelength range, holding the key for overcoming diffraction limits in optics, and hence, fundamental advances in electronics and information processing. 32,33 These shape requirements for NPs within the interesting nanometer scale have proven difficult to achieve. 34,35 Apart from obvious scientific and technological value, asymmetric angled shapes for noble metals are elusive because of the highly sym- metrical face-centered cubic (fcc) crystal lattice in which they crystallize, typically resulting in equally symmetrical NPs. Notably, Au NP synthesis within templates, which might have given an opportunity to produce more complex shapes by removing the intrinsic crystallization tendencies, also revealed the challenging nature of angled shapes. Most of the examples of *To whom correspondence should be addressed. E-mail: lmarzan@uvigo.es (L.M.L.-M.); kotov@umich.edu (N.A.K.). (1) Ozbay, E. Science 2006, 311, 189–193. (2) Park, J.; Joo, J.; Kwon, S.; Jang, Y.; Hyeon, T. Angew. Chem., Int. Ed. 2007, 46, 4630–4660. (3) Liz-Marz an, L. M. Langmuir 2006, 22, 32–41. (4) Tao, A.; Habas, S.; Yang, P. Small 2008, 4, 310–325. (5) Skrabalak, S.; Chen, J.; Sun, Y.; Lu, X.; Au, L.; Cobley, C.; Xia, Y. Acc. Chem. Res. 2008, 41, 1587–1595. (6) Chen, J.; Wiley, B.; Xia, Y. Langmuir 2007, 23, 4120–4129. (7) Murphy, C. J.; Sau, T.; Gole, A.; Orendorff, C.; Gao, J.; Gou, L.; Hunyadi, S.; Li, T. J. Phys. Chem. B 2005, 109, 13857–13870. (8) P erez-Juste, J.; Pastoriza-Santos, I.; Liz-Marz an, L. M.; Mulvaney, P. Coord. Chem. Rev. 2005, 249, 1870–1901. (9) Millstone, J.; Hurst, S. J.; Traux, G. S. M.; Cutler, J. I.; Mirkin, C. A. Small 2009, 5, 646–664. (10) Pastoriza-Santos, I.; Liz-Marz an, L. M. J. Mater. Chem. 2008, 18, 1724– 1737. (11) Grzelczak, M.; P erez-Juste, J.; Mulvaney, P.; Liz-Marz an, L. M. Chem. Soc. Rev. 2008, 37, 1783–1791. (12) Pastoriza-Santos, I.; Liz-Marz an, L. M. Adv. Funct. Mater. 2009, 19, 679– 688. (13) Kujala, S.; Canfield, B. K.; Kauranen, M.; Svirko, Y.; Turunen, J. Opt. Express 2008, 16, 17196–17208. (14) Drozdowicz-Tomsia, K.; Xie, F.; Calander, N.; Gryczynski, I.; Gryczynski, K.; Goldys, E. M. Chem. Phys. Lett. 2009, 468, 69–74. (15) Tabor, C.; Murali, R.; Mahmoud, M.; El-Sayed, M. J. Phys. Chem. A 2009, 113, 1946–1953. (16) Ali Umar, A.; Oyama, M. Cryst. Growth Des. 2009, 9, 1146–1152. (17) Nehl, C.; Hafner, J. J. Mater. Chem. 2008, 18, 2415–2419. (18) Wang, S.; Lu, W.; Tovmachenko, O.; Rai, U. S.; Yu, H.; Ray, P. C. Chem. Phys. Lett. 2008, 463, 145–149. (19) Sonavane, G.; Tomoda, K.; Makino, K. Colloid Surf. B 2008, 66, 274–280. (20) Murphy, C.; Gole, A.; Stone, J.; Sisco, P.; Alkilany, A.; Goldsmith, E.; Baxter, S. Acc. Chem. Res. 2008, 41, 1721–1730. (21) Katz, E.; Willner, I. Angew. Chem., Int. Ed. 2004, 43, 6042–6108. (22) Hu, M.; Chen, J.; Li, Z.; Au, L.; Hartland, G.; Li, X.; Marquez, M.; Xia, Y. Chem. Soc. Rev. 2006, 35, 1084–1094. (23) Anker, J.; Hall, W.; Lyandres, O.; Shah, N.; Zhao, J.; Van Duyne, R. Nat. Mater. 2008, 7, 442–453. (24) De, M.; Ghosh, P.; Rotello, V. Adv. Mater. 2008, 20, 4225–4241. (25) Jain, P.; Huang, X.; El-Sayed, I.; El-Sayed, M. Acc. Chem. Res. 2008, 41, 1578–1586. (26) Stewart, M.; Anderton, C.; Thompson, L.; Maria, J.; Gray, S.; Rogers, J.; Nuzzo, R. Chem. Rev. 2008, 108, 494–521. (27) Veselago, V. G. Sov. Phys. USPEKHI-USSR 1968, 10, 509–514. (28) Soukoulis, C.; Kafesaki, M.; Economou, E. Adv. Mater. 2006, 18, 1941– 1952. (29) Smith, D.; Pendry, J. B.; Wiltshire, M. C. K. Science 2004, 305, 788–792. (30) Shalaev, V. M. Nat. Photonics 2007, 1, 41–48. (31) Yao, J.; Liu, Z.; Liu, Y.; Wang, Y.; Sun, C.; Bartal, G.; Stacy, A. M.; Zhang, X. Science 2008, 321, 930. (32) Pendry, J. B.; Smith, D. R. Phys. Today 2004, 57, 37–43. (33) Valentine, J.; Zhang, S.; Zentgraf, T.; Ulin-Avila, E.; Genov, D.; Bartal, G.; Zhang, X. Nature 2008, 455, 376–379. (34) Xia, Y.; Xiong, Y.; Lim, B.; Skrabalak, S. E. Angew. Chem., Int. Ed. 2009, 48, 60–103. (35) Matsubara, S.; Hayakawa, T.; Yang, Y.; Nogami, M.; Okamoto, S.; Koshikawa, N. J. Phys. Chem. C 2008, 112, 13917–13921.