Ujjal Kumar Sur Ujjal Kumar Sur

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http://dx.doi.org/10.5772/66084

#### **Abstract**

The steady and fast development of surface and interfacial science have set up innovative openings for new diagnostic probes for analytical characterization of the adsorbates and determination of the microscopic structure of surfaces and interfaces. Regrettably Raman spectroscopy, being a weak scattering surface phenomenon, had seized no part in it, until the discovery and development of Surface Enhanced Raman Scattering (SERS) in the early 1970's that has opened up broad research fields both in the physics and chemistry of interfaces. The discovery of SERS by Fleischmann and coworkers in 1974 at the University of Southampton, United Kingdom is closely connected with the electrochemical systems. They reported an extraordinary million-fold enhancement of weak Raman signal from pyridine molecules adsorbed onto electrochemically roughened silver electrode compared to that from free molecules in liquid environment. In early 1976, Richard P. Van Duyne and David Jeanmaire at Northwestern University observed the effect and in early 1977, M. G. Albrecht and J. A. Creighton reported similar observation. This review article deals with the development of SERS research with special importance is given to the fabrication of various SERS-active substrates, mechanism of SERS effect and its various potential applications ranging from sensors to biomedical applications.

**Keywords:** Raman scattering, surface-enhanced Raman scattering, electromagnetic (EM) enhancement effect, hot spots, sensors, SERS active substrates

## **1. Introduction**

Raman scattering arises as a result of interaction of electromagnetic radiation with matter resulting in the alteration of frequency or wavelength of the incident radiation. With the invention of strong, monochromatic, polarized and tunable lasers, the Raman spectroscopy has grown as a highly sensitive technique to probe structural details of a complex molecular structure. However, the applications of traditional or conventional Raman spectroscopy are restricted by the low scattering cross section involved with the Raman scattering process,

© 2016 The Author(s). Licensee InTech. 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. © 2017 The Author(s). Licensee InTech. 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.

which are ~ 12–14 orders of magnitude lower than the fluorescence cross section for various biological and organic molecules, which are highly fluorescent in nature [1–7]. Therefore, the discovery of Fleischmann and coworkers from the University of Southamption, UK in 1974 [8], which demonstrated the unexpected high Raman signals obtained from pyridine molecules adsorbed on a rough silver electrode, has attracted considerable attention of researchers from various fields such as physics, chemistry, biology, mathematics, and engineering. In a published paper, Fleischmann et al. reported an extraordinary million-fold enhancement of Raman signal from pyridine molecules adsorbed onto electrochemically roughened silver electrode compared to that from free molecules in a liquid environment [8]. Surface-enhanced Raman scattering (SERS) effect deals with the gigantic amplification of the weak Raman scattering intensity by molecules in the presence of a nanostructured metallic surface [5–8]. The SERS enhancement factor can be defined as the ratio between the Raman signals obtained from a given number of molecules in the presence and in the absence of the metal nanostructure and this factor is dependent largely on the size and morphology of the nanostructures. In general, SERS enhancement value is around 106 , but it may reach value as high as 1010 at definite highly effective subwavelength regions of the surface [5–8].

Since its discovery in the year 1974, surface-enhanced Raman scattering (SERS) has attracted significant interest of researchers [1–7]. The discovery of SERS has opened up a promising way to overcome the low-sensitivity problem associated with conventional Raman spectroscopy. Introduction of the SERS technique not only improves the overall surface sensitivity making Raman spectroscopy more applicable but also stimulates the study of the interfacial processes involving enhanced optical scattering from adsorbates on metal surfaces [9].

This review article covers the current development in SERS research along with brief discussion on the fabrication of various SERS active substrates, the various theoretical explanations of the mechanism of SERS effect and its various diverse applications in sensing, diagnostics, and catalysis. The article first deals with a short historical assessment of the SERS effect, followed by an overview on the preparation of various SERS active substrates. The article concludes with the citations of some recent applications of SERS from the literature. Due to insufficiency in space, a comprehensive review of all current work based on SERS is impossible. However, we have summarized a few representative examples including our own results to demonstrate the recent advancement in the SERS research.
