Electrochemical SERS and its Application in Analytical, Biophysical and Life Science

Abstract

Raman spectroscopy, as a vibrational spectroscopy, can record fingerprint spectra from electrodes and provide much insight into a variety of surface and interfacial processes at the molecular level: for example, qualitatively determining surface bonding, conformation and orientation. Raman spectroscopy invariably uses lasers from the ultraviolet (UV) to the near infrared (NIR). More importantly, the technique can be applied in situ to investigate solid-liquid, solid-gas and solid-solid interfaces of both fundamental and practical importance. The technique can be used flexibly to study porous electrode materials of high surface area, to which many surface techniques are not applicable. Therefore, Raman spectroscopy is among the most promising methods for use in electrochemistry. The major disadvantage of Raman spectroscopy is its very low detection sensitivity. However, surface-enhanced Raman scattering (SERS) can improve the sensitivity significantly by several orders of magnitude for roughened surfaces of many metals including noble and transition metals.This chapter will first introduce some fundamental background and features of electrochemical surface-enhanced Raman scattering (EC-SERS), followed by a detailed description of the experimental setup for electrochemical Raman spectroscopy and preparation of SERS substrates. The emphasis will be on how to obtain reliable information of very sensitive bio-related systems. Some examples, varying from a model molecule of benzene to real biomolecules, such as dopamine, NADH, DNA and cytochrome c (cyt c), will be shown to demonstrate how to apply EC-SERS for bio-related application. Finally, prospects and further developments of EC-SERS application in bio-related systems will be discussed. Electrochemical Surface-Enhanced Raman SpectroscopyThe first SERS spectra were obtained from an electrochemical cell when Fleischmann et al. tried to roughen the Ag electrode in order to increase the surface area and hence the number of adsorbed pyridine molecules on the laser spot [1]. This phenomenon was soon demonstrated to be due to the surface enhancement effect

Electrochemical surface oxidation enhanced Raman scattering

“…Raman spectroelectrochemistry [14][15][16][17] (TR-Raman SEC) is used to follow the roughening process of silver with a Raman probe molecule in the electrolytic solution, being possible to detect transient processes [18][19][20]. Thus, SERS SEC system allows both, the electrochemical investigation and also the simultaneous SERS data, and therefore presents wide applicability in target molecules analysis with low detection limit.…”

Probing single molecules and molecular aggregates: Raman spectroscopic advances

“…Simply considering |E| 4 , a maximum enhancement E max for a single molecule adsorbed on an isolated Ag nanoparticle is not larger than 10 8 , whereas the EM enhancement for a nanoparticle dimer can be up to ~10 11 . This enhancement is comparable with the necessary precondition for observing an SMR event although this estimation has ignored charge transfer, possible resonance effect and long‐range coupling effect from the nanoparticle aggregations . If considering all these contributions, a total enhancement factor for SMR could be up to ~10 14 .…”

“…On optimized substrates, a concentration limitation up to ~10 −15 or ~10 −16 M has been attained for SMR observation of certain analytes . Moreover, it was indicated that metal electrode systems could also support SMR events, but concentration limit is a challenge …”