Single-Crystalline-Mesoporous TiN Nanosheets Free of Intrinsic Raman Scattering for Highly Sensitive Surface-Enhanced Raman Spectroscopy

Compared with metal surface-enhanced Raman spectroscopy (SERS) substrates that exhibit no intrinsic Raman signals, nonmetallic SERS substrates often introduce bothersome background interference due to their strong inherent Raman scattering. Herein, we report the synthesis of single-crystalline mesoporous (SCM) TiN nanosheets─with a thickness of merely 2 nm─as a nonmetallic SERS substrate that is free of intrinsic Raman signals. To fabricate these unique SCM nanosheets, we developed a mixed-molten-salt nitridation strategy that incorporates both inert (KCl) and reactive (ZnCl₂) molten salts. The Zn₃N₂ thin layer formed in situ via the nitridation of the reactive molten salt not only facilitates the formation of SCM-TiN nanosheets but also effectively suppresses the high-temperature sintering of the TiN nanosheets. As a nonmetallic SERS substrate, the SCM-TiN nanosheets exhibit an ultrahigh Raman enhancement factor of 2.71 × 10⁸, an ultralow detection limit of 2.0 × 10^-13 M, excellent signal reproducibility, and remarkable durability in corrosive environments. A particularly valuable finding is that the SCM-TiN nanosheets themselves have no intrinsic Raman signals, which eliminates the background interference commonly associated with traditional nonmetallic substrates and thus provides a strategy for the design of high-performance SERS substrates.