Polyelectrolyte Multilayer-Mediated Growth of Gold Nanoparticle Films with Tunable Loading Density and Nanoparticle Shape Hye Young Koo, Won San Choi, Jeong-Ho Park, Dong-Yu Kim * Introduction Metal nanoparticle films have been the subject of numerous scientific reports in recent years, because of their unique size-dependent optical and electronic proper- ties. [1] Gold nanoparticle (AuNP) films are of particular interest because of the strong plasmon resonance absorp- tion of AuNP in the visible wavelength. [2] The various approaches used for the integration of AuNPs into thin films can be classified into two categories: 1) Top-down: direct growth on a planar surface by evaporation or the sputtering of atomic gold under a vacuum, by electro- chemical deposition; [3] 2) Bottom-up: self-assembly of preformed AuNPs from solution by spin coating, con- vective assembly, Langmuir-Blodgett method, directed self-assembly on an water-oil interface, [4] etc. Benefiting from numerous studies of well-established wet chemical syntheses of stable AuNPs in solution, bottom-up fabrica- tion may offer better controllability of the size and shape of AuNPs compared to the top-down method. However, the direct adsorption of AuNPs onto substrates from a solution generally suffers from non-uniform distribution because of the aggregation of AuNPs when they form layers on a substrate upon the loss of solvent. To circumvent this problem, many previous studies have been conducted using appropriate binding molecules or polymers for controlling the distribution of AuNPs on substrates. [5] Recently, Aslan et al. [6] reported the direct growth of silver nanoparticles on planar surfaces using a seed- mediated growth approach, analogous to the solution synthesis of AuNPs reported by Jana et al. [7] This approach was demonstrated to be a simple and relatively rapid method for preparing a nanostructured silvered thin film, compared to other expensive and sophisticated methods such as lithography. Communication A facile method for preparing gold nanoparticle (AuNP) films with a high loading density based on the seed-mediated growth of AuNPs on a polyelectrolyte multilayer (PEM) is reported. Use of PEMs as a base layer for gold seed adsorption confers controllability on the loading density of the AuNP film and size of the resulting AuNPs. In addition, the shape of the final AuNPs could be varied by adapting various species of polyelectrolytes. The optical res- ponse of the AuNP films is stable, because of the relatively uniform distribution of the AuNPs over a large area. The AuNP film has been used as a substrate for surface-enhanced Raman scattering (SERS), and it shows stable and reproducible enhancement in the range from 10 5 to 10 7 depending on the fabrication condition. H. Y. Koo, J.-H. Park, D.-Y. Kim Heeger Center for Advanced Materials (HCAM), Department of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju 500712, South Korea Fax: þ82 62 970 2304; E-mail: kimdy@gist.ac.kr W. S. Choi Melville Laboratory, Department of Chemistry, Lensfield road, University of Cambridge, Cambridge, CB2 1EW, UK 520 Macromol. Rapid Commun. 2008, 29, 520–524 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/marc.200700683