Sustainable AuNPs@GO Paper-Based SERS Platform with Integrated Chromatography for Point-of-Care Environmental Sensing

Developing versatile surface-enhanced Raman scattering (SERS) substrates for complex environmental analysis requires balancing mechanical robustness, sensitivity, and sustainability. Here, we report a flexible composite paper comprising GO and TEMPO-oxidized cellulose nanofibers (TOCNs) decorated with in situ grown gold nanoparticles (AuNPs). Notably, the TOCNs are derived from recycled Kaoliang sorghum dregs, valorizing an abundant agro-industrial residue into a high-crystallinity fibrous scaffold. Uniform nucleation of ∼10 nm AuNPs across the GO@TOCN matrix establishes dense plasmonic centers, while the resulting film exhibits a 7- to 8-fold increase in tensile strength compared to pristine TOCN paper, maintaining integrity under deformation. The substrate achieves limits of detection below 10^-7 M for rhodamine 6G and direct blue. This sensitivity arises from a synergistic mechanism coupling electromagnetic hotspots between proximal AuNPs with chemical enhancement driven by analyte-GO charge transfer and fluorescence quenching. Furthermore, tuning the GO/TOCN ratio enables on-paper chromatographic separation of mixed analytes prior to Raman interrogation, enhancing signal resolution. By integrating sustainable feedstock, mechanical durability, and chromatographic enrichment with ultrasensitive readout, this platform offers a scalable solution for multiplexed point-of-care diagnostics and environmental monitoring.