1T/2H-MoS₂ Nanoclusters as Plasmon-Free Surface-Enhanced Raman Spectroscopy Substrates for Ultrasensitive Detection of Environmental Pollutants

Surface-enhanced Raman spectroscopy (SERS) holds immense promise for molecular detection, yet the quest for high-performance, plasmon-free substrates remains active. This work pioneers the rational design and engineering of phase-tunable MoS₂ nanoclusters─metallic (1T), semiconductor (2H), and, critically, hybrid metal/semiconductor (1T/2H) phases as a novel class of SERS platforms. We demonstrate this exceptional capability for ultrasensitive detection of environmentally hazardous dyes (e.g., rhodamine B, crystal violet, and methylene blue). Remarkably, the optimized 1T/2H-MoS₂ substrate achieves an enhancement factor of 1.02 × 10⁹, which ranks among the higher values for SERS substrates derived from semiconductors. Crucially, time-resolved transient photoluminescence decay spectroscopy reveals a dramatic 52% decrease in average exciton lifetime (from 3.88 to 1.86 ns) for RhB adsorbed on 1T/2H-MoS₂ substrates. This profound decrease provides direct evidence for highly efficient interfacial charge transfer, predominantly driven by the built-in electric field unique to the engineered phase junction. Furthermore, by leveraging the distinct Raman signatures enabled by this heterophase substrate, we achieve the multiplex detection of all five environmental nucleobases (adenine, guanine, cytosine, thymine, and uracil) in both individual and mixed solutions. This work not only delivers fundamental mechanistic insights into charge transfer-mediated SERS but also provides a practical platform with broad implications for environmental monitoring, biomedical diagnostics, and analytical chemistry.