Three-dimensional SERS hot spots for chemical sensing: Towards developing a practical analyzer

Robust surface-enhanced Raman scattering (SERS) detection of chemicals in real environmental samples remains a huge challenge because of the use of a complex unknown sample, low molecular affinity for metal surface, or the inefficient use of hot spots. The controlling of hot spots for SERS enhancement has led to an in-depth development of various plasmonic nanostructures. Recently, three-dimensional (3D) hot spots are actively pursued to increase the number and efficiency of hot spots in all three dimensions. This study summarizes the recent progress in the fabrication of novel 3D plasmonic nanostructures and discusses the evolution of flexible and liquid-state designs of 3D hot spots, which have recently emerged as a promising SERS technique. Finally, we present a prospective overview for challenges and future perspectives. Although not exhaustive, this study presents some of the most interesting methodologies for fabricating and controlling 3D hot spots and assists researchers in understanding the evolution and challenges in this field, thereby furthering interest in developing chemical-sensing SERS techniques.