Emerging 2D Materials and Their Hybrid Nanostructures for Label-Free Optical Biosensing: Recent Progress and Outlook

The increasing demand for rapid detection and remote monitoring with high sensitivity and selectivity has driven the development of label-free optical biosensors based on 2D materials (2DMs). Owing to their high surface-to-volume ratio and unique, tunable electrical and optical properties, 2DMs are highly attractive for biosensing applications. Van der Waals heterostructures (vdWHs) that combine different 2DMs allow the creation of hybrid materials with synergistic or novel functionalities. Beyond purely 2D vdWHs, mixed-dimensional hybrid architectures have recently emerged, offering enhanced sensitivity, stability, and reproducibility in label-free optical detection. This review highlights recent advances in surface-enhanced Raman scattering (SERS)- and surface plasmon resonance (SPR)-based biosensing using 2DMs and their hybrid nanostructures, discussing the role of each component and emphasizing their synergistic effects. It also provides an overview of recent progress in multifunctional sensing platforms and the integration of machine learning to improve performance and enable intelligent data analysis. Finally, the current challenges and future opportunities for advancing next-generation label-free optical biosensors are highlighted.