SERS: Materials, applications, and the future

The first observations of the Raman spectra of pyridine on roughened silver were made in 19741; however, at this time the authors did not recognize that these spectra were due to any unusual, enhanced, or new phenomena. Since its discovery in 19772, interest in and the use of surface enhanced Raman spectroscopy (SERS) has grown exponentially (Fig. 1). The SERS field has dramatically progressed from the originally observed enhancement on roughened silver electrodes to the current fields of sensing and imaging applications, single molecule detection, and extensions to ultrahigh vacuum and ultrafast science3-6. At the most basic level, SERS is a way to significantly increase the signal from the weak yet structurally rich technique of Raman scattering. Researchers have implemented several methods to increase the Raman scattering efficiency, including using stimulated Raman processes and electronic resonance enhancement; however, the most significant amplification of the Raman signal comes from SERS7-10. At its most complex level, single molecules are now routinely observed due to the large enhancement. Additionally, SERS is an exceptional technique for the characterization of small numbers of molecules bound to or near plasmonic surfaces. As SERS enters its fourth decade, we review here several of the most exciting findings and new avenues in this field. In this article, we Surface enhanced Raman spectroscopy (SERS) is a powerful vibrational spectroscopy technique that allows for highly sensitive structural detection of low concentration analytes through the amplification of electromagnetic fields generated by the excitation of localized surface plasmons. SERS has progressed from studies of model systems on roughened electrodes to highly sophisticated studies, such as single molecule spectroscopy. We summarize the current state of knowledge concerning the mechanism of SERS and new substrate materials. We highlight recent applications of SERS including sensing, spectroelectrochemistry, single molecule SERS, and real-world applications. We also discuss contributions to the field from the Van Duyne group. This review concludes with a discussion of future directions for this field including biological probing with UV-SERS, tip-enhanced Raman spectroscopy, and ultrafast SERS.