Total volatile basic nitrogen (TVB-N) content is the most widely used index for the assessment of fish freshness. Herein, a smartphone-integrated colorimetric sensor of TVB-N is developed based on a functional hydrogel loaded with Au@MnO2 core-shell nanocomposites and beta-D-glucose pentaacetate (beta-D-GP). In the sensing hydrogel, Au@MnO2 serves as a colorimetric substance and beta-D-GP is a precursor of reducing agent. TVB-N can permeate the sensing hydrogel, causing an alkaline environment in which beta-D-GP is hydrolyzed to produce beta-D-glucose. A redox reaction between MnO2 and beta-D-...
