Preparation of an aramid nanofiber-reinforced colorimetric hydrogel employing natural anthocyanin as an indicator for shrimp and fish spoilage monitoring

In this study, a colorimetric hydrogel with a strong network employing natural anthocyanin as an indicator was developed for visual monitoring of shrimp and fish spoilage. Polyvinyl alcohol (PVA) and sodium alginate (SA) were used as matrix models to prepare functional hydrogels with a double network structure by a simple freezing/thawing process and calcium cross-linking in SA. To enhance the strength of the hydrogel, aramid nanofibers (ANFs) were introduced which were obtained from aramid fibers by a deprotonation method. The natural anthocyanin extract was extracted from purple cabbage by a hot water soaking method and acted as the color sensing substance in the hydrogel. Smartphone-based RGB color analysis showed good color response of the hydrogel indicators to amines. Various characterization methods revealed that the hydrogel also had good thermal stability, mechanical properties, and water resistance. The hydrogels exhibited good performance for the spoilage monitoring of shrimp and fish through correlation analysis, indicating that they are promising candi-dates for sensing applications.