**1. Introduction**

There has been a long-standing interest in the application of metallic nanoparticles (NPs), in particular of gold (Au) and silver (Ag), due to their unique optical properties [1–6]. The dispersion of very small (submicrometric to nanometric) metal particles in materials that act as host matrices (e.g. glass) has been empirically exploited to confer bright and colorful effects, resulting from scattering and absorption of visible light. In fact, there are several examples of earlier technological applications that include the use of fine divided gold in glass materials in order to obtain beautiful colors, such as in stained glass windows [7, 8]. Nowadays, metal NPs are considered crucial in a series of devices derived from nanotechnological approaches

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

and which are expected to expand in the near future in several applications and techniques. Among these techniques, Surface Enhanced Raman Scattering (SERS) has emerged in the past decades with great importance. Although the discovery of the SERS effect dates back to the 70's, [9] in the last decades, this technique has been improved due to the huge progress observed in Raman instrumentation and also in recent research specific to nanoscale materials. Indeed, the design of SERS active and highly sensitive analytical platforms has been a major goal in several fields, due to the impact in trace chemical analysis, environmental monitoring, medical applications and food safety [10–16].

surface. A few years later, other research groups advanced the currently accepted explanation for this observation [33, 34]. The interpretation given considered that the Raman signal intensification occurred due to adsorption of molecules on rough metallic surfaces. It is generally accepted today that the intensification occurring in SERS is due to two distinct mechanisms: the chemical interaction of the analyte with the metallic surface (signal intensification 10–10<sup>2</sup>

SERS Research Applied to Polymer Based Nanocomposites

http://dx.doi.org/10.5772/intechopen.72680

and the enhancement of the local electric field at the junction of the metallic NPs (signal intensification can reach up to 10<sup>11</sup>) [32, 35, 36]. The chemical mechanism (CM) for the SERS signal enhancement is related to the adsorption of molecular species on the metal surface, namely the surface selection rules, the type of interaction between the metal and the molecule and the chemical nature of the adsorbed molecule itself [36–38]. The electromagnetic mechanism (EM) is the dominant contribution to SERS and does not depend necessarily on the establishment of a chemical interaction between the analyte and the metal surface, contrary to what happens in the chemical mechanism. According to the EM, the intensification of the local electromagnetic field is mainly due to the excitation of the surface plasmons of the metal by the incident light [39–41]. While the CM is a short-range effect, the EM is a long-range effect, in the sense that it does not require that the molecular species is in contact with the metal surface and can still be observed a few nanometers of distance from the metal surface. **Figure 1** presents a scheme of

**Figure 1.** (A) Scheme illustrating the chemical mechanism (CM) that occurs in SERS. (a) Ground state chemical

local electromagnetic field; HOMO represents the highest occupied molecular orbital and LUMO represents the lowest unoccupied molecular orbital); (B) Scheme illustrating the electromagnetic mechanism (EF), in which the I represents

represents the incident electric field; Ei,s represents the field which is intensified by the metal

+ Er,s) represents the scattered enhanced field. ([10] - Reproduced by permission of The Royal

represents the scattered Raman field, which can be intensified by

enhancement; (b) resonance Raman enhancement; (c) charge-transfer resonance enhancement, where Ef

the intensity of Raman; E<sup>i</sup>

the metal creating Er,s; (E<sup>r</sup>

Society of Chemistry.).

+ Ei,s) represents the incident enhanced field; E<sup>r</sup>

and (E<sup>i</sup>

)

93

represents the

This chapter intends to present recent developments concerning polymer based nanocomposites containing metal nanofillers for SERS applications, in some situations based on studies of metal loaded polymers prepared in our laboratory. In order to contextualize the SERS application of these polymer based nanocomposites, the synthesis of the nanostructures and some fundamental aspects of SERS are briefly introduced [17–25]. Polymer based composites for SERS, containing metallic fillers, have been largely documented for the vestigial detection of several bio-analytes. Illustrative examples on the use of polymer based composites as new platforms for SERS are described in more detail, reviewing their use for chemical analysis. The importance of Raman imaging in SERS studies is also explored because is a recent development with a great potential for the research on new SERS substrates.
