Two-dimensional materials in surface-enhanced Raman spectroscopy: from fundamental mechanisms to sensing applications

Surface-Enhanced Raman Spectroscopy (SERS) is an ultrasensitive molecular detection technique whose signal amplification arises from two principal mechanisms: electromagnetic enhancement (EM) and chemical enhancement (CM). In recent years, two-dimensional (2D) materials, including graphene, transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), and MXenes, have emerged as highly promising candidates for SERS substrate fabrication, owing to their distinctive atomic-scale thickness, large specific surface area, tunable electronic structures, and exceptional chemical stability. In this review, we systematically survey the latest advances in SERS research involving both standalone 2D material substrates and their hybrid systems with metallic nanostructures, with particular emphasis on the physical underpinnings of EM and CM enhancement mechanisms. Special attention is devoted to several frontier topics, including the coupling physics between plasmonic near-fields and the electronic systems of 2D materials, hot-carrier injection dynamics, exciton-plasmon strong coupling, and phonon-assisted enhancement. Furthermore, the application of theoretical computational approaches, such as finite-difference time-domain (FDTD) simulations and density functional theory (DFT) calculations in mechanistic elucidation is discussed. Finally, key challenges confronting the field and prospective future directions are outlined.