The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.

Experimental results obtained in different laboratories world‐wide by researchers using surface‐enhanced Raman scattering (SERS) can differ significantly. We, an international team of scientists with long‐standing expertise in SERS, address this issue from our perspective by presenting considerations on reliable and quantitative SERS. The central idea of this joint effort is to highlight key parameters and pitfalls that are often encountered in the literature. To that end, we provide here a series of recommendations on: a) the characterization of solid and colloidal SERS substrates by correlative electron and optical microscopy and spectroscopy, b) on the determination of the SERS enhancement factor (EF), including suitable Raman reporter/probe molecules, and finally on c) good analytical practice. We hope that both newcomers and specialists will benefit from these recommendations to increase the inter‐laboratory comparability of experimental SERS results and further establish SERS as an analytical tool.

Using picosecond excitation at 1064 nm, surface-enhanced hyper-Raman scattering (SEHRS) spectra of the nucleobases adenine, guanine, cytosine, thymine, and uracil with two different types of silver nanoparticles were obtained. Comparing the SEHRS spectra with SERS data from the identical samples excited at 532 nm and with known infrared spectra, the major bands in the spectra are assigned. Due to the different selection rules for the one- and two-photon excited Raman scattering, we observe strong variation in relative signal strengths of many molecular vibrations obtained in SEHRS and SERS spectra. The two-photon excited spectra of the nucleobases are found to be very sensitive with respect to molecule–nanoparticle interactions. Using both the SEHRS and SERS data, a comprehensive vibrational characterization of the interaction of nucleobases with silver nanostructures can be achieved.

Determining the catalytic activity and the reaction kinetics are key issues when new catalysts are developed, characterized, and introduced. Catalysis at the nanoscale employing nanoparticles has great potential because of their new catalytic properties, high surface-to-volume ratios, and high surface reactivity. [1] In principle, reactions at the surface of metal structures can be studied using molecular surfacespecific spectroscopic techniques. [2] The most versatile of these is surface-enhanced Raman scattering (SERS), which has been frequently applied in investigations of different types of reactions at electrochemical interfaces in situ [3] to address, for example, the formation of reaction intermediates, [4] the dependence of electroorganic reactions on electrode potential, [5] and electron transfer in protein systems. [6] Herein we demonstrate that SERS can be used to study directly the kinetics of a catalytic reaction in situ. Our approach is novel by allowing the structural characterization of the reactant and product surface species in the reaction as well as investigating rate constants in the same experiment. This was possible by using separate gold and platinum nanoparticles that were simultaneously attached to the same glass surface. Our method is independent of the optical absorption properties of the reaction products and/or the catalysts.In order to investigate a metal-catalyzed reaction with SERS or other plasmon-supported approaches, [7] bifunctional metal structures are needed that have plasmonic properties and also act as a catalyst. [8] A number of catalytically active composite nanostructures have been reported to enhance the Raman signals of dye molecules, [9] and SERS has been used to monitor the structural evolution of bimetallic catalytically active Au-Pt nanoparticles. [10] However, direct observations of a catalytic process by SERS have been rare as they require bifunctional nanomaterials. [11] Our approach is different from those previously reported based on composite nanostructures with plasmonic (Au) and catalytic (Pt, [11a] or Pd) [11b] properties, as we have used separate gold and platinum nanoparticles that are simultaneously immobilized on a glass surface. Scanning tunneling microscopy (STM) data indicate that owing to the proximity of the platinum and gold nanoparticles, the molecules can interact with the platinum nanoparticles whilst they reside in the local optical fields provided by the localized surface plasmons of the gold nanoparticles. The versatility, stability, and general applicability of the immobilized gold nanoparticles for studying catalytic reactions are demonstrated by the quantification of the reaction products and the determination of the kinetics with different catalysts. The results reported therefore have implications both for basic catalysis research and analytical applications.Gold nanoparticles 40 nm in diameter and platinum nanoparticles less than 2 nm in diameter were prepared by reported procedures. [12] Mixtures of these gold and platinum nano...