Defect-induced enhanced Raman scattering of two-dimensional materials

Two-dimensional (2D) materials have emerged as compelling candidates for noble-metal-free surface-enhanced Raman scattering (SERS) substrates due to their atomic-scale thickness, tunable electronic properties, superior optical characteristics, and biocompatibility. While noble metal substrates rely on the electromagnetic mechanism (EM), defect engineering of 2D materials offers a transformative strategy to amplify their molecular sensing capabilities through the chemical mechanism (CM). This review article introduces defect-induced enhanced Raman scattering (DiERS) as a novel paradigm, where engineered defects in 2D materials—such as vacancies, dopants, grain boundaries, and heterostructures—precisely regulate charge transfer processes and molecular interactions. We systematically analyze defect generation methods across graphene and transition metal dichalcogenides (TMDCs), emphasizing scalable synthesis techniques (e.g., CVD, plasma etching) and advanced characterization tools (STEM, STM, CAFM) for atomic-level defect visualization. The core mechanisms of DiERS are elucidated through two critical pathways: (1) light-matter interactions, where defects modulate band structures to enhance resonant charge transfer, and (2) defect-matter interactions, involving defect-mediated adsorption and dipole effects that amplify molecular polarization. Furthermore, we highlight the potential applications of DiERS in ultrasensitive detection of environmental toxins (e.g., heavy metal ions, dyes), food contaminants (pesticides, additives), and biomedical diagnostics (neurotransmitters, viral proteins), achieving detection limits as low as 10^-18 M. Challenges and future directions—including large-scale defect uniformity, standardized quantification protocols, and AI-driven spectral analysis—are discussed to advance DiERS toward next-generation molecular diagnostics and industrial scalability.