609 © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 1. Introduction The emerging field of nano-optics has raised interest towards the properties of collective excitations in metal nano- structures, commonly known as surface plasmons. [1–3] The Synergistic Modulation of Surface Interaction to Assemble Metal Nanoparticles into Two-Dimensional Arrays with Tunable Plasmonic Properties Lin Jiang,* Changji Zou, Zhonghan Zhang, Yinghui Sun, Yueyue Jiang, Wanru Leow, Bo Liedberg, Shuzhou Li, and Xiaodong Chen* properties of surface plasmons are related to the cumula- tive effect of size, shape, and spacing of the metal nanostruc- tures. [4–9] The most widely studied configurations are ordered array nanostructures composed of metal nanoparticles with tunable inter-particle distance. These can serve as ideal plat- forms for developing active plasmonic devices for applica- tions in biosensing, [10–14] optoelectronics, [15–17] catalysis, [18,19] toxic ion detection, [20–26] and optical antennas. [27–29] Several approaches have been devised to fabricate such plasmonic nanostructures, including top-down lithographic techniques, such as e-beam lithography. [30,31] However, these techniques are limited by low throughput, high cost, and high surface roughness of small features, [32] which restrict their employ- ment in potential applications. On the other hand, various bottom-up methods, such as colloidal approaches based on template-directed and interfacial self-assembly, pro- vide intriguing alternatives for assembling plasmonic nano- particles into ordered arrays with desirable properties. [33–38] Interfacial self-assembly, without any template assistance, is particularly attractive for constructing large area two-dimen- sional (2D) ordered arrays with predefined inter-particle dis- tance. [39–41] For example, well-ordered and closely-packed 2D metal nanoparticle arrays have been prepared by controlled DOI: 10.1002/smll.201302126 A simple strategy based on the synergistic modulation of inter-particle and substrate- particle interaction is applied for the large-scale fabrication of two-dimensional (2D) Au and Ag nanoparticle arrays. The surface charge of the substrate is used to redistribute the double layer electric charges on the particles and to modulate the inter- particle distance within the 2D nanoparticle arrays on the substrate. The resultant arrays, with a wide range of inter-particle distances, display tunable plasmonic properties. It can be foreseen that such 2D nanoparticle arrays possess potential applications as multiplexed colorimetric sensors, integrated devices and antennas. Herein, it is demonstrated that these arrays can be employed as wavelength-selective substrates for multiplexed acquisition of surface-enhanced Raman scattering (SERS) spectra. This simple one step process provides an attractive and low cost strategy to produce high quality and large area 2D ordered arrays with tunable properties. Plasmonics Prof. L. Jiang Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices Institute of Functional Nano & Soft Materials (FUNSOM) Soochow University Suzhou, Jiangsu, 215123, China E-mail: ljiang@suda.edu.cn Prof. L. Jiang, C. Zou, Z. Zhang, Dr. Y. Sun, Y. Jiang, W. Leow, Prof. B. Liedberg, Prof. S. Li, Prof. X. Chen School of Materials Science and Engineering Nanyang Technological University 50 Nanyang Avenue, Singapore, 639798, Singapore http://www.ntu.edu.sg/home/chenxd/ E-mail: chenxd@ntu.edu.s C. Zou, Prof. B. Liedberg, Prof. X. Chen Center for Biomimetic Sensor Science Nanyang Technological University 50 Nanyang Drive, Singapore, 637553, Singapore small 2014, 10, No. 3, 609–616