Surface-Enhanced Raman Scattering Based on Noble Metal Nanoparticles - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 250

chapter reviews the enhancement mechanisms that lead to SERS and
discuss the important methods used to strengthen the effect. The
chapter then focuses on recent reports of the achievements of metal
NP-based SERS in bioanalytical applications with speciic attention
given to its use in pathogen detection and bioimaging.
11.1 Introduction
Raman spectroscopy is a vibrational technique which provides a
wealth of information on the molecular species under interrogation.
Its many ields of application include identiication and structural
characterization of semiconductor materials, authentication of
artifacts and legal documentations, quality control in pharmaceutical
manufacturing, and the development of new biophysical tools for
disease diagnosis and health monitoring. A major disadvantage of
Raman spectroscopy is the inherently small scattering cross section
of the Raman process, which is typically 12-14 orders of magnitudes
smaller than luorescence cross-sections. This was why the
observation of an unexpectedly large Raman signals from pyridine
adsorbed on roughened Ag electrode surprised researchers in the
ield. In 1974, Fleischmann et al. reported intense Raman scattering
from pyridine adsorbed onto a Ag electrode roughened through
repeated oxidation-reduction cycles in an attempt to develop an
in situ monitoring tool that is chemically speciic. 2 The authors
attributed the large pyridine Raman signal to the increase in number
of molecules adsorbed on the increased surface area of the roughened
Ag electrode. In 1977, Van Duyne et al. recognized that the large
intensity observed could not be accounted for by the increase in the
number of scatterers and proposed an electric ield enhancement
model to account for their observation. 3 Ultimately, it was the 1978
report by Moskovits, in which he put forward an interpretation
in terms of electromagnetic resonances in the form of a localized
surface plasmon resonance (LSPR) in noble metal nanostructures
that paved the way for the electromagnetic enhancement theory
as it is currently understood. 4 In that same report, Moskovits also
predicted that a similar intense SERS signal would be observable in
colloid metal NPs. Concurrently, Albrecht and Creighton in their 1977
report speculated that resonance Raman scattering from molecular
electronic states, broadened by their interaction with metal surface,
could be responsible for the increased intensity. 5