  Plasmon-free surface-enhanced Raman scattering (SERS) substrates have
attracted tremendous attention for their abundant sources, excellent chemical
stability, superior biocompatibility, good signal uniformity, and unique
selectivity to target molecules. Recently, researchers have made great progress
in fabricating novel plasmon-free SERS substrates and exploring new enhancement
strategies to improve their sensitivity. This review summarizes the recent
developments of plasmon-free SERS substrates and specially focuses on the
enhancement mechanisms and strategies. Furthermore, the promising applications
of plasmon-free SERS substrates in biomedical diagnosis, metal ions and organic
pollutants sensing, chemical and biochemical reactions monitoring, and
photoelectric characterization are introduced. Finally, current challenges and
future research opportunities in plasmon-free SERS substrates are briefly
discussed.
