Abstract
Raman spectroscopy has enabled researchers to map the specific chemical makeup of surfaces, solutions, and even cells. However, the inherent insensitivity of the technique makes it difficult to use and statistically complicated. When Raman active molecules are near gold or silver nanoparticles, the Raman intensity is significantly amplified. This phenomenon is referred to as surface-enhanced Raman spectroscopy (SERS). The extent of SERS enhancement is due to a variety of factors such as nanoparticle size, shape, material, and configuration. The choice of Raman reporters and protective coatings will also influence SERS enhancement. This review provides an introduction to how these factors influence signal enhancement and how to optimize them during synthesis of SERS nanoparticles.
Highlights
Raman spectroscopy is a vibrational spectroscopy technique that has great promise for the identification of solids, liquids, and gases
This paper provides an introduction to how these factors influence enhancement factor (EF) (Sections 2 and 3) and how to control them during synthesis (Sections 4 and 5)
The optimization of SERS nanoparticles to achieve the highest enhancement factor is a complex process that incorporates multiple variables which must be precisely controlled by synthesis methods
Summary
Raman spectroscopy is a vibrational spectroscopy technique that has great promise for the identification of solids, liquids, and gases. The chemical enhancement mechanism is caused by molecular charge-transfer interactions between the molecule and the metallic surface [7, 8] Together, these mechanisms of enhancement increase the Raman intensity to a point where SERS can be used for applications which require greater molecular sensitivity. An illustration of a nanoparticle used for extrinsic SERS is provided, where a Raman reporter molecule is bound to the metal surface and encased in a protective layer. Calculations for metallic spherical nanoparticles have predicted that the SERS intensity will decay with increasing distance, r, between the target molecule and particle surface. To synthesize SERS nanoparticles with an optimal EF for intrinsic applications, it is requisite to understand how a nanoparticle’s material, size, shape, and configuration influence EFs. Synthesis of nanoparticles for extrinsic SERS applications requires additional understanding of how Raman reporters and protective layers influence EF. This paper provides an introduction to how these factors influence EF (Sections 2 and 3) and how to control them during synthesis (Sections 4 and 5)
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