The origin of ultrasensitive SERS sensing beyond plasmonics

Plasmon-free surface-enhanced Raman scattering (SERS) substrates have\nattracted tremendous attention for their abundant sources, excellent chemical\nstability, superior biocompatibility, good signal uniformity, and unique\nselectivity to target molecules. Recently, researchers have made great progress\nin fabricating novel plasmon-free SERS substrates and exploring new enhancement\nstrategies to improve their sensitivity. This review summarizes the recent\ndevelopments of plasmon-free SERS substrates and specially focuses on the\nenhancement mechanisms and strategies. Furthermore, the promising applications\nof plasmon-free SERS substrates in biomedical diagnosis, metal ions and organic\npollutants sensing, chemical and biochemical reactions monitoring, and\nphotoelectric characterization are introduced. Finally, current challenges and\nfuture research opportunities in plasmon-free SERS substrates are briefly\ndiscussed.\n