Bioinspired Janus-Structured Surface-Enhanced Raman Scattering Mask with Dual‑Scale Heterointerface for Ultrasensitive Exhaled H2S Detection in Periodontitis Diagnosis

The accurate detection of hydrogen sulfide (H2S) in exhaled breath is important for the early diagnosis of periodontitis; however, it is limited by high humidity in the oral environment, contaminant accumulation, and multicomponent interference. Herein, we present a Janus-structured surface-enhanced Raman scattering (SERS) platform featuring a dual-scale heterogeneous interface inspired by the asymmetric wettability of lotus leaves for sensitive detection of ppb-level H2S. Specifically, thermal treatment of polypropylene melt-blown fabric precoated with polydimethylsiloxane (PDMS) induces hydrophobic residue migration, converting the surface to superhydrophobic. Moreover, the PDMS layer promotes dense growth of MgAl layered double hydroxide (LDH) nanosheets followed by Ag nanoparticle deposition, constructing the superhydrophilic SERS functional side. The spatially heterogeneous wettability design achieves diode-like unidirectional liquid transport properties, effectively resisting signal interference at 90% relative humidity in exhaled breath. Importantly, the gradient pore architecture functions as a molecular deceleration layer, retarding the diffusion of high-kinetic-energy H2S and enriching it within the hotspots of the MgAl LDH/Ag nanocavities, yielding a limit of detection of 1.54 ppb. Clinical exhaled breath analysis has confirmed that this sensor integration strategy in KN95 masks exhibits feasibility and accuracy, holding promise as an effective technical means for early noninvasive screening and clinical diagnosis.