Fabrication of densely-packed nanoparticle layers@ cellulose nanofibril nanopaper via interface self-assembly and its SERS application.

Cellulose-based surface-enhanced Raman spectroscopy (SERS) substrates have emerged as a prominent research focus for advancing the practical application of SERS technology. Herein, a three-phase interfacial self-assembly strategy was developed to deposit nanoparticle layers onto the surface of cellulose nanofibril (CNF) nanopapers. This approach enables the fabrication of large-area monolayer or multilayer metallic nanoparticles (NPs) with diverse morphologies on the CNF surface, thereby constructing versatile SERS nanopapers with tunable surface plasmonic properties. The double-layered Au NPs@CNF nanopaper showed excellent SERS performance, achieving a minimum detectable concentration (MDC) of 10-13 M (4-aminothiophenol, 4-ATP) and 0.1 ppm (methamphetamine, MAMP) with a wide linear range. Featuring excellent optical transparency and a well-defined porous structure, the substrate facilitates efficient extraction and enrichment of target analytes. By attaching its non-metallic side to sample surfaces, it enables SERS detection as well as food-safe, nondestructive trace analysis. As a proof of concept, these SERS nanopapers were applied to rapidly detect thiram on apple peels, with an MDC of 0.1 ng/cm2, and to extract and identify dyes from textiles with minimal damage. These approaches prevent nanoparticle contamination on food surfaces and eliminate destructive sampling, providing a reliable and biosafe strategy for nondestructive in-situ SERS monitoring.