Hierarchical Pore Engineering Overcomes Diffusion Barriers in SERS Gas Sensors for 1 ppt-Level Bacterial Viability Monitoring

The diffusion limitation at the gas-solid interface remains a critical challenge hindering the advancement of surface-enhanced Raman scattering (SERS) for gas analysis. To address this issue, this study proposes a gas-flow modulation strategy based on a hierarchical pore metastructure (HPMS), which optimizes the mass transfer of gas molecules to the solid-phase SERS substrate and elucidates the synergistic mechanism between mass transfer and sensing performance in SERS systems. This approach is successfully applied to live bacterial metabolic monitoring. Fluid dynamics simulations reveal that the HPMS effectively increases the analyte concentration near the SERS substrate surface, concurrently enhancing the area-averaged velocity through the formation of a lateral concentration gradient. Electromagnetic field simulations further confirm that the in situ growth of Ag nanoparticles within the pores generates three-dimensional (3D) plasmonic hot spots, effectively increasing the hot spot density and enhancing the longitudinal laser utilization efficiency. Leveraging this strategy, a detection sensitivity of 1 part per trillion (ppt) is achieved for the gaseous bacterial metabolite dimethyl disulfide (DMDS), along with real-time monitoring capability for bacterial viability within 30 min. The proposed HPMS-based modulation strategy provides a universal solution for gas detection using solid SERS substrates, offering significant potential for advancing SERS-based gas analysis technologies.