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.

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic.

Gold nanostars are multibranched nanoparticles with sharp tips, which display extremely interesting plasmonic properties but require optimization. We present a systematic investigation of the influence of different parameters on the size, morphology, and monodispersity of Au nanostars obtained via seeded growth in concentrated solutions of poly(vinylpyrrolidone) in N,N-dimethylformamide. Controlled prereduction of Au(3+) to Au(+) was found to influence monodispersity (narrower plasmon bands), while the [HAuCl(4)]/[seed] molar ratio significantly affects the morphology and tip plasmon resonance frequency. We also varied the size of the seeds (2-30 nm) and found a clear influence on the final nanostar dimensions as well as on the number of spikes, while synthesis temperature notably affects the morphology of the particles, with more rounded morphologies formed above 60 °C. This rounding effect allowed us to confirm the importance of sharp tips on the optical enhancing behavior of these nanoparticles in surface-enhanced raman scattering (SERS). Additionally, the sensitivity toward changes in the local refractive index was found to increase for larger nanostars, though lower figure of merit (FOM) values were obtained because of the larger polydispersity.