Quantitative SERS Methods

Abstract

The goal of transforming SERS from an interesting novelty into a viable quantitative analytical technique has been pursued for many years, but it is only recently that the first indications that quantitative SERS could be generally achievable have appeared. Up to this point, the challenges of preparing sensitive and reproducible enhancing media and the need to develop a deep understanding of the fundamental mechanisms of the effect (or at least to have a working knowledge of the relationship between the microstructure of the enhancing materials, their surface chemistry and the enhancements that they provide; see also Chapter 1) have been sufficient to occupy the attention of researchers who were interested in using SERS for quantitative measurements. However, many of these issues have now either been fully resolved or at least brought to the stage where they are no longer impediments. For example, new generations of enhancing media have been developed; the links between microstructure, plasmon resonances and enhancements have been established; and the role of the media's surface chemistry is being addressed. This chapter discusses these new developments and also considers the extent to which the separate strands can be combined to create standard, generally applicable methods for quantitative SERS. In addition, it highlights the need to begin the process of judging the success of new SERS methods against competing technologies, rather than against previous SERS results. SERS MediaThe choice of enhancing media for SERS studies has grown to an extraordinary extent, although they can still be broadly divided into solution-phase suspensions of nanoparticles and micro-textured solid substrates. This division dates back to the earliest work in the area, which used either colloidal suspensions of silver or gold nanoparticles [1] or the surfaces of roughened noble-metal electrodes [2]. Since this

Heparin Assisted Photochemical Synthesis of Gold Nanoparticles and Their Performance as SERS Substrates

“…Most colloidal metal particles prepared by the reduction of metal salts (in our case, photochemically) carry a negative charge as a result of an adsorbed layer of stabilizing anions, so they will be electrostatically attracted to the nanoparticles surface. If the target molecule carries the same charge as the nanoparticle, it will not interact electrostatically with the metal surface, but still, it can make contact with it by displacing an existing ion from a site on the surface [ 27 ]. Table 1 , Table 2 and Table 3 indicate the corresponding peak assignments; we determined non-referenced peaks.…”

Quantitative Analysis of Entacapone Isomers Using Surface-Enhanced Raman Spectroscopy and Partial Least Squares Regression

“…The internal standard compensates for variations in signal intensity, caused by laser power drift or alignment variations, is introduced even within conventional Raman analysis. 8 To avoid perturbations of the measured system, an adequate internal standard in SERS should be a molecule chemically similar to the analyte, which must bind to the enhancement substrate in the same way the analyte does. 8 SERS quantification experiments on thymine and nicotine used chemically similar and well-studied pyridine as an internal standard.…”

“…8 To avoid perturbations of the measured system, an adequate internal standard in SERS should be a molecule chemically similar to the analyte, which must bind to the enhancement substrate in the same way the analyte does. 8 SERS quantification experiments on thymine and nicotine used chemically similar and well-studied pyridine as an internal standard. 9,10 However, since pyridine is not chemically similar to entacapone and binds through pyridine nitrogen to the metal surface, and entacapone binds through the cyano group, pyridine was not introduced into the system.…”

“…Quantitative SERS applications, on the other hand, have been reported to a lesser extent because of the lack of reproducible and stable SERS substrates to ensure reliable SERS measurements. 8,–12 Nevertheless, because of the huge effort being put into finding novel methods for substrate preparation, control over shape and size as well as reproducibility have been introduced in the preparation process, resulting in the production of highly reliable substrates. 8…”

Polystyrene Beads as Probes of the Surface-Enhanced Raman Scattering Response Characteristics of Silver Nanorod Arrays

“…Surface-enhanced Raman scattering (SERS) is a powerful analytical tool for determining analyte concentration and characterizing the vibrational, rotational, and other lowfrequency modes of molecules and molecular ensembles. [1][2][3] Historically, a major impediment to its application was the difficulty involved in manufacturing SERS substrates with reproducible performance characteristics. Recently, substrates comprised of silver nanorod arrays have been shown to be highly uniform in structure, easy to fabricate, and provide strong, highly reproducible, signal enhancements.…”