A ratiometric indicator pad utilizing Alz/BRI-PVA for visual assessment of fish freshness

In this study, a novel intelligent water-absorbent cellulose pad with a specified area was developed for the visual and non-destructive monitoring of fish freshness. The pad’s substrate was composed of wood pulp cellulose (WPC), and the specified area contained a ratiometric mixture of brilliant blue (BRI) and alizarin (Alz)., fixed with Polyvinyl alcohol (PVA). During the freshness monitoring process, the Alz/BRI-PVA WPC pad exhibited a color transition from green to brown, followed by a shift to purple-red, corresponding to the increasing levels of total volatile base nitrogen (TVB-N) and total viable count (TVC). After testing, a BRI/Alz ratio of 1:8 was selected as the optimal ratio. Compared to the volatile gas-based sensing tags, the pad developed in this study demonstrated a high sensitivity of 53.4% by interacting with the sample exudate to produce signal changes. This study demonstrates the feasibility of using the developed dual-functional pad for water absorption and freshness indications. • A dual functional pad with indicating and water-absorbing properties is developed. • The indicating area shows color changes for visual detection of freshness. • The indicating area is more sensitive due to the Alz/BRI ratiometric indicator. • The indicating area can change color from green to brown, and then to purple.