Surface Enhanced Raman Scattering Spectroscopy

This review covers from the basic principles of Raman spectroscopy to the advanced technique of surface enhanced Raman Scattering (SERS) spectroscopy. After briefly going through the description of Raman and introduction of the development of SERS, the article will focus on the “hotspot” of the current research work on SERS – single molecule spectroscopy. We will see later that “hotspot” is also frequently used to describe the place where SERS happens. This vague description in some extent reflects the ambiguity and controversy in the understanding of the phenomenon. However, single molecule SERS provides us a possible way to disclose the secret. Single molecule spectroscopy is not only a novel tool to explore the properties of the molecules; it also shines light on the further understanding the SERS itself. Research work from several groups in this field was introduced. There are lots of other applications for SERS in the bioscience, which is beyond the scope of this short paper. Only the application of SERS studying the surface adsorption and detection of DNA and RNA were presented to give some flavors in this research field. Finally, what can we do with SERS? In the last part of the paper, the topic of doing SERS on the flat surface was discussed. This is not only of intellectual fun, but may also give us great advantages to develop new techniques. One example is to combine the SERS with surface force apparatus (SFA) study, which requires two smooth flat surfaces. Unfortunately smooth flat surface is the killer of the enhancement. Then here we try to rescue. Only little mathematics was given for the illustration of the principles of Raman. The electromagnetic explanation of SERS will definitely be demonstrated better with equations, which however falls beyond my background and knowledge. At last, two references are strongly recommended to those who want a good introductory but not too out-of-date material. One is the handout for MIT class by Katrin Kneipp. She is one of the earliest researchers who work on the single molecule SERS. Another is a free online journal called “the internet journal of vibrational spectroscopy” with a featured issue on SERS. Here is the link: http://www.ijvs.com/volume4/edition2/index.html