A facile method for the synthesis of large-size Ag nanoparticles as efficient SERS substrates Yang Zhao, a Yue-Jiao Zhang, a Jin-Hui Meng, a Shu Chen, b Rajapandiyan Panneerselvam, a Chao-Yu Li, a Sain Bux Jamali, a Xia Li, c * Zhi-Lin Yang, b Jian-Feng Li a * and Zhong-Qun Tian a Silver nanoparticles (Ag NPs) enjoy a reputation as an ultrasensitive substrate for surface-enhanced Raman spectroscopy (SERS). How- ever, large-scale synthesis of Ag NPs in a controlled manner is a challenging task for a long period of time. Here, we reported a simple seed-mediated method to synthesize Ag NPs with controllable sizes from 50 to 300 nm, which were characterized by scanning elec- tron microscopy (SEM) and UV–Vis spectroscopy. SERS spectra of Rhodamine 6G (R6G) from the as-prepared Ag NPs substrates indi- cate that the enhancement capability of Ag NPs varies with different excitation wavelengths. The Ag NPs with average sizes of ~150, ~175, and ~225 nm show the highest SERS activities for 532, 633, and 785-nm excitation, respectively. Significantly, 150-nm Ag NPs exhibit an enhancement factor exceeding 10 8 for pyridine (Py) molecules in electrochemical SERS (EC-SERS) measurements. Further- more, finite-difference time-domain (FDTD) calculation is employed to explain the size-dependent SERS activity. Finally, the potential of the as-prepared SERS substrates is demonstrated with the detection of malachite green. Copyright © 2016 John Wiley & Sons, Ltd. Additional supporting information may be found in the online version of this article at the publisher’s web site. Keywords: surface-enhanced Raman scattering; large-size; silver nanoparticles; seed-mediated method; Rhodamine 6G Introduction Surface-enhanced Raman spectroscopy (SERS), as a powerful spec- troscopy technique, provides intrinsic chemical and fingerprint infor- mation about the target molecules. [1–14] With its single molecule sensitivity and selectivity, this technique has attracted considerable interests among the research community for chemical and biological sensing. [15–18] In SERS, the Raman signals of the target molecules are greatly enhanced when they are located at or very close to a certain SERS-active metal nanostructures. The most commonly used SERS substrates include Ag, Au, and Cu nanomaterials. Since Faraday first prepared Au colloids in 1856, [19] nanomaterials have garnered a significant attention because of their potential applications in catalysis, bio-labeling, sensing, photonics, optoelectronics, etc. As the physical and chemical properties of nanomaterials are deter- mined and limited by the distribution of their physical dimensions and shapes, so how to control their size and morphology has been the primary research interest in the past few decades. [20–29] Various synthetic strategies have been developed in order to get desired op- tical and surface properties with the plasmonic nanoparticles. [30–39] Surface plasmon resonance (SPR), the collective oscillations of the conduction electrons in plasmonic nanostructures, decides the huge enhancement of Raman signals in SERS. [40–43] The optical excitation of the surface plasmons create a strong electromagnetic (EM) field at the interface and surface of plasmonic nanoparticles, which aug- ments the Raman signals of the adsorbed/target molecules. Among the three most commonly used metals (Ag, Au, and Cu), the surface plasmon efficiency of Ag is greater than Au and Cu NPs. Another advantage of Ag over Au is that the SPR of Ag nanostructures can be tuned to any wavelength in the visible region of the spectrum. In addition, Ag is much cheaper than Au. For instance, Tian et al. reported a method for preparing Au-seed Ag-growth nanoparticles of controllable diameter (50–100 nm) at room temperature and characterized their morphological, optical, and material properties. [44,45] The report verified that the Ag NPs exhibit at least two orders of magnitude greater enhancement than Au NPs when excited with green light on a smooth Ag surface. However, based on the SEM images, the Ag NPs synthesized were not homogeneous in size or shape, which evidently leads to poor reproducibility in SERS measurements. Moreover, SERS studies on Ag NPs with sizes larger than 100 nm are very limited, because it is dif- ficult to synthesize larger Ag nanoparticles with controllable size and good uniformity. [27,32] Therefore, it is desirable to develop some new methods for large-scale preparation of uniform and size-controlled Ag NPs with high reproducibility, and stability in a large scale. * Correspondence to: Xia Li, Technology Center, China Tobacco Zhejiang Industrial Co. Ltd., Hangzhou 31024, China. E-mail: lix@zjtobacco.com * Correspondence to: Jian-Feng Li, MOE Key Laboratory of Spectrochemical Analysis and Instrumentation, State Key Laboratory of Physical Chemistry of Solid Surfaces, Innovation Center of Chemistry for Energy Materials, and College of Chemistry and Chemical Engineering, Xiamen, China. E-mail: li@xmu.edu.cn a MOE Key Laboratory of Spectrochemical Analysis and Instrumentation, State Key Laboratory of Physical Chemistry of Solid Surfaces, Innovation Center of Chemistry for Energy Materials, and College of Chemistry and Chemical Engineering, Xiamen, China b Department of Physics, Xiamen University, Xiamen 361005, China c Technology Center, China Tobacco Zhejiang Industrial Co. Ltd, Hangzhou 31024, China J. Raman Spectrosc. (2016) Copyright © 2016 John Wiley & Sons, Ltd. Research article Received: 6 November 2015 Revised: 15 December 2015 Accepted: 16 December 2015 Published online in Wiley Online Library (wileyonlinelibrary.com) DOI 10.1002/jrs.4879