A SERS-Colorimetric Gas Sensor Utilizing Silica−Alginate Hydrogel and Nanorods for Continuous Monitoring of Fish Freshness

Abstract The continuous monitoring of food freshness is an effective strategy for mitigating public health concerns stemming from food spoilage. However, conventional testing methodologies necessitate the disruption of the packaging and the preliminary processing of the food item, thereby rendering them primarily applicable to professional management. In this study, we propose a SERS-colorimetric freshness sensor for the continuous detection of spoilage gases in fish products. The sensor was encapsulated in the form of a warning label with alginate-modified silica hydrogel, which can be sealed within the food package. Thus, throughout the entire lifecycle of fish products, their freshness can be directly estimated by visual inspection. Meanwhile, the embedded gold-coated silver nanorods modified with 4-MBA enable professional supervision of spoilage gases using a handheld Raman spectrometer. Furthermore, the silica−alginate hydrogel absorbing spoilage gases and steam could retard the deterioration of fish. Overall, this approach with flexible readout demonstrates the potential to support end-to-end real-time monitoring of fish products.