“Four-in-One” Surface-Enhanced Raman Scattering Hydrogel Sensor Integrating Sieving, Enrichment, Capturing, and Calibration for Food Spoilage Monitoring

Accurate monitoring of volatile biogenic amines is critical for early food spoilage warning yet hindered by the low adsorption and small intrinsic Raman cross sections of gaseous molecules. Herein, we constructed a surface-enhanced Raman scattering (SERS) hydrogel platform based on Au nanostars@4-mercaptobenzaldehyde@ZIF-8 (AuNSs@4-MBA@ZIF-8) to monitor cadaverine and putrescine. This rationally designed hierarchical core-shell architecture is further integrated into a flexible hydrogel network. This architecture synergizes metal-organic framework (MOF)-assisted molecular sieving and nanoenrichment with the Schiff base-mediated transformation of weakly scattering amines into highly Raman-active conjugated molecules. Simultaneously, the 4-MBA reporter serves as a built-in internal standard for reliable ratiometric calibration. Benefiting from this quadruple "sieving-enrichment-capturing-calibration" strategy, the sensor exhibits excellent detection performance for both liquid and gaseous amines, achieving broad dynamic ranges spanning 5 orders of magnitude. In addition, it was successfully applied to the in situ monitoring of real meat spoilage via direct conformal contact, demonstrating its excellent promise for detecting trace volatile markers in complex environments for food safety.