Vibrational Spectroscopy 68 (2013) 246–250 Contents lists available at ScienceDirect Vibrational Spectroscopy jou rn al hom ep age: www .elsevier.com/locate/vibspec Surface-enhanced Raman scattering of 4-aminobenzenethiol on silver nanoparticles substrate Elias de Barros Santos, Fernando Aparecido Sigoli, Italo Odone Mazali ∗ Laboratory of Functional Materials, Institute of Chemistry, University of Campinas – UNICAMP, P.O. Box 6154, 13083-970 Campinas, SP, Brazil a r t i c l e i n f o Article history: Received 6 May 2013 Received in revised form 31 July 2013 Accepted 1 August 2013 Available online 26 August 2013 Keywords: Silver nanoparticles 4-ABT Raman spectroscopy SERS a b s t r a c t Active surface-enhanced Raman scattering (SERS) silver nanoparticles substrate was prepared by mul- tiple depositions of Ag nanoparticles on glass slides. The substrate is based on five depositions of Ag nanoparticles on 3-aminopropyl-trimetoxisilane (APTMS) modified glass slides, using APTMS sol–gel as linker molecules between silver layers. The SERS performance of the substrate was investigated using 4- aminobenzenethiol (4-ABT) as Raman probe molecule. The spectral analyses reveal a 4-ABT Raman signal enhancement of band intensities, which allow the detection of this compound in different solutions. The average SERS intensity decreases significantly in 4-ABT diluted solutions (from 10 -4 to 10 -6 mol L -1 ), but the compound may still be detected with high signal/noise ratio. The obtained results demonstrate that the Ag nanoparticles sensor has a great potential as SERS substrate. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Surface-enhanced Raman spectroscopy (SERS) is an analytical technique extensively used in chemistry, biology, forensics, and materials science, due to its excellent molecular vibrations sensitiv- ity [1–4]. The surface-enhanced effect in metals surface adsorbed molecules can provide results that are several orders of magni- tude higher than normal Raman scattering signal [5,6]. The signals amplification in SERS comes, mainly, through the electromagnetic interaction between the radiation and the localized surface plas- mon (LSP) in noble metal surface structures. Another contribution arises from the charge transfer energy of the molecules adsorbed and/or very close to the metal surface [5,6]. High electromag- netic fields can be generated when nanostructured metals (e.g. Ag, Au, and Cu) substrates are excited by light, generally in the visible range, causing LSP generation. This fact has significantly contributed to SERS to be considered an ultra-sensitive trace detec- tion technique [7] or even as a single-molecule probing tool [8,9]. Since the discovery of the enhanced Raman effect by Fleischmann [10], a lot of research has been directed to the development of efficient SERS substrates such as metal electrodes, Ag, Au, and Cu colloidal nanoparticles, and lithographically made substrates [11–14]. However, many of those substrates do not offer Raman signal reproducibility, which is a well-known difficulty when SERS is used as an analytical spectroscopy technique. ∗ Corresponding author. Tel.: +55 19 3521 3095; fax: +55 19 3521 3023. E-mail address: mazali@iqm.unicamp.br (I.O. Mazali). In fact, there are large variety of SERS substrates pre- pared through many different methodologies such as colloidal suspensions synthesis, metal vapor depositions, and lithogra- phy [12,14,15]. Lithographically made substrates can provide an excellent control on density and position of the hot spots. However, those substrates have some limitations such as high cost and long preparation time [15,16]. Some articles repor- ting the use of 3-mercaptopropyl-trimethoxysilane (MPTMS) and 3-aminopropyl-trimethoxysilane (APTMS) to functionalize SERS substrates were published in recent years [17–19]. These com- pounds have chemical groups, such as SH and NH 2 that can chemically interact with Au and Ag nanoparticles. For example, after modifying a glass slide with MPTMS or APTMS a layer of gold or silver nanoparticles can be attached on the modified surface. Using this strategy, one moiety of bifunctional molecule could anchor to the first nanoparticles layer through a surface polymeriza- tion procedure, leaving another moiety “available” to immobilize nanoparticles from a colloidal solution via chemical bonding. A hierarchical structure can be built through repeating this proce- dure [19]. Generally this procedure achieves multi-layers and/or aggregates structures, creating hot spots on the substrate surface. This kind of material has typically been applied as SERS substrate with promise results [18,19]. However, in the scientific literature still have few investigations about the influence of experimental parameters on Raman signal such as nanoparticle size and analyte concentration. In this work, SERS active substrates based on multiple deposi- tions of Ag nanoparticles onto APTMS modified glass slides were prepared. Samples with five depositions of silver nanoparticles were used as a SERS substrate with 4-aminobenzethiol as the 0924-2031/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.vibspec.2013.08.003