Portable functional hydrogels based on silver metallization for visual monitoring of fish freshness

A simple, cost-effective and non-destructive sensing strategy is developed to real-time monitor the biogenic amines (BAs) for evaluating the food spoilage. This sensing strategy is performed on a functional hydrogel, which is fabricated by β-d-glucose pentaacetate (β-D-GP), silver ions and agarose hydrogel. The β-D-GP serves as a reducing agent precursor because it can be hydrolyzed into β-d-glucose under alkaline environment of BAs exposure. The as-prepared β-d-glucose further reduces silver ions (Ag+) to silver nanoparticles (Ag0) along with the color changes. The color changes can be distinguished by naked eyes, and digitized by a smartphone combined with RGB (red/green/blue) analysis. The (R + G + B)/B gray value of hydrogel is used to not only quantify the BAs vapor, but also successfully assess the freshness of actual sample. Compared to other previously reported BAs sensors, this strategy circumvents the pre-synthesis of fluorescence/colorimetric probe in advance, making its more economical and practical for monitoring the freshness of fish.