Fabrication of aptamer-mediated Fe₃O₄@AuNPs magnetic capture and Ag-enhanced SERS nanoplatforms for bacterial detection.

Rapid and sensitive detection of pathogenic bacteria is essential for infection control and clinical diagnostics, yet conventional methods remain limited by low sensitivity and inefficient enrichment in complex samples. Herein, we develop an aptamer-mediated magnetic capture and surface-enhanced Raman scattering (SERS) nanoplatform based on Fe₃O₄@Au nanocomposites and Ag nanoparticles (AgNPs) for bacterial detection. Fe₃O₄@Au is functionalized with specific aptamers to enable selective magnetic enrichment, while AgNPs modified with reporter aptamers act as SERS enhancers, forming a sandwich-like Fe₃O₄@Au-bacteria-Ag architecture. This integrated system combines efficient target capture with plasmonic amplification, where magnetic separation increases bacterial concentration and minimizes matrix interference. Meanwhile, the confined coupling between Au and Ag nanostructures generates dense electromagnetic hotspots, significantly enhancing Raman signals. Mechanistically, dual-aptamer recognition ensures high specificity, and the nanoscale interparticle gaps promote localized surface plasmon resonance coupling, leading to amplified electromagnetic fields. The platform exhibits high sensitivity, selectivity, and reproducibility, enabling reliable bacterial identification in complex environments. This work provides a robust strategy for coupling magnetic enrichment with SERS amplification, offering promising potential for rapid pathogen detection and advanced biosensing applications.