Raman spectroscopy is a widely used analysis tool first introduced by Sir. C. V. Raman to identify molecular structures by detecting Raman scattering phenomenon, a form of inelastic scattering when incident photons hit a molecule. The resulting Raman spectrum serves as a characteristic fingerprint of a specific molecule, allowing highly accurate identification of unknown molecules. Surface-enhanced Raman spectroscopy(SERS) is a technique where surface morphology of metallic structures are modified to increase the Raman signal intensity by several orders of magnitude. Studies on plasmonic nanostructures for SERS have shown single-molecule level sensitivities, and thus SERS has risen as a strong candidate for the detection of trace-amount molecules owing to its rapid, facile, nondestructive nature of measurement and high sensitivity. Signal enhancement in SERS mainly depends on the localized surface plasmon resonance(LSPR) effect. LSPR, a non-propagating surface plasmon, occurs at the surface of isolated metallic nanostructures. For example, at the curved surface of a metal nanoparticle or nano-sized gaps between metallic nanostructures electron clouds oscillate upon incident light, forming “hot spots” where local electromagnetic fields are greatly amplified. For the design of effective SERS structures, key requirements include high-density and reproducible distribution of strong “hot spots”, and the use of an efficient fabrication method.
3D Cross-point nanostructure 
Concentric ring nanostructure
Further reading
“Selective, Quantitative, and Multiplexed Surface‐Enhanced Raman Spectroscopy Using Aptamer‐Functionalized Monolithic Plasmonic Nanogrids Derived from Cross‐Point Nano‐Welding” Advanced Functional Materials, 2020, 2000612 Seunghee H. Cho, Kwang Min Baek, Hyeuk Jin Han, Minjoon Kim, Hyungjoon Park and Yeon Sik Jung* [Link]
“3D Cross-point Plasmonic Nano-architectures Containing Dense and Regular Hot Spots for Surface-Enhanced Raman Spectroscopy Analysis“ Advanced Materials, 2016, 28, pp 8695-8704 Jae Won Jeong, Md Masud Parvez Arnob, Kwang-Min Baek, Seung-Yong Lee, Wai-Chuan Shih and Yeon Sik Jung* [Link]
“Sequentially Self-Assembled Rings-in-Mesh Nanoplasmonic Arrays for Surface-Enhanced Raman Spectroscopy” Chemistry of Materials, 2015, 27, 14, pp.5007-5013 Kwang Min Baek, Jong Min Kim, Jae Won Jeong, Seung Yong Lee*, and Yeon Sik Jung* [Link]