A novel natural SERS substrate based on microfibrillated silk: Rapid adsorption and trace detection of methylene blue in aqueous systems

In this study, an effective biomass-based surface-enhanced Raman scattering (SERS) substrate was developed by combining microfibrillated silk (MFS) derived from Bombyx mori silk fibers with silver nanoparticles (AgNPs). The substrate was prepared through an environmentally friendly in situ reduction strategy based on the intrinsic reducing ability of MFS. The resulting AgNPs@MFS composites, prepared using different silver nitrate concentrations, were characterized, and their SERS performances were evaluated using model Raman probe molecules. The surface charge of AgNPs@MFS could be tuned by adjusting the solution pH, which promoted efficient enrichment of target molecules on the substrate, with an adsorption efficiency of 48.1% for methylene blue. The substrate exhibited excellent SERS performance, with a lowest detectable concentration of 1 × 10 −9  M for methylene blue. In addition, it showed preferential adsorption toward cationic dye molecules. The substrate also demonstrated reliable SERS detection in realistic water samples (tap water and lake water) with satisfactory recovery, highlighting its applicability in complex aqueous matrices. These results indicate that MFS provides a simple and scalable SERS platform through its hierarchical structure, adsorption capability, and in situ nanoparticle growth, enabling robust detection of target molecules in real-world aqueous environments.