<p>Surface-enhanced Raman scattering (SERS) has emerged as a powerful plasmonic sensing strategy owing to its ability to amplify molecular vibrational signatures through localized surface plasmon resonance (LSPR)-induced electromagnetic enhancement. In this work, a flexible paper-based plasmonic substrate was developed by immobilizing Tollens-derived silver nanoparticles (AgNPs) onto cellulose filter paper through a simple immersion-coating process. UV–Vis spectroscopy revealed a characteristic LSPR absorption band centered at 405&#xa0;nm, while FE-SEM analysis demonstrated the formation of densely packed AgNP assemblies on the cellulose fibers. The hierarchical roughness of the paper matrix combined with nanoscale interparticle gaps generated abundant plasmonic hot spots capable of producing strong localized electromagnetic fields. The plasmonic performance of the substrate was evaluated through SERS-based detection of <i>Acinetobacter baumannii</i>. Distinct Raman fingerprints were successfully detected over a bacterial concentration range spanning 10¹–10¹⁰ CFU. The fabricated substrate exhibited an experimental enhancement factor of 2.41 × 10⁶ at 1595&#xa0;cm^− 1 and achieved a detection limit of 10¹ CFU. Reproducibility studies yielded a relative standard deviation of 4.31% from five independent measurements, confirming excellent signal uniformity across the plasmonic surface. The observed enhancement is attributed to efficient electromagnetic coupling within the AgNP assemblies and the resulting high-density hot-spot network distributed throughout the cellulose scaffold. These findings demonstrate that AgNP-decorated filter paper provides a low-cost, flexible, and highly effective plasmonic architecture for ultrasensitive SERS biosensing and pathogen detection.</p> Graphical Abstract <p></p>