Label-Free SERS Identification of <i>Listeria monocytogenes</i> Based on Plasmonic Actuators-Coupled Three-Dimensional TiO ₂ Nanoarchitectures

The development of high-performance substrates is crucial for promoting the practical application of surface-enhanced Raman scattering (SERS) in biodetection. This study investigates the critical role of titanium dioxide (TiO 2 ) support morphology on the SERS performance of Au@Ag nanoparticle-based substrates. We synthesized spherical TiO 2 microspheres (S-TiO 2 ) and three-dimensional flower-like TiO 2 nanoarchitectures (F-TiO 2 ) and uniformly decorated them with Au@Ag nanoparticles (NPs). Systematic evaluation using probe molecules (Rhodamine 6G, Methylene Blue) demonstrated that the F-TiO 2 /Au@Ag substrate exhibited dramatically enhanced SERS activity compared to its spherical counterpart, which is attributed to the larger surface area and more complex three-dimensional structure of the nanoflowers that facilitate higher-density loading of Au@Ag NPs (plasmonic actuators) and create a greater number of electromagnetic “hot spots”. When applied to the label-free detection of the foodborne pathogen Listeria monocytogenes, the optimized F-TiO 2 /Au@Ag substrate achieved an outstanding detection limit of 5 CFU/mL, with a wide linear range from 10 3 to 10 8 CFU/mL. This work not only provides a highly sensitive SERS platform for pathogen detection but also underscores the paramount importance of rational morphology engineering of semiconductor supports in the design of next-generation sensing materials.