Development of peptide impregnated V/Fe bimetal Prussian blue analogue as Robust nanozyme for colorimetric fish freshness assessment.

Colorimetric sensing is a low-cost and visual method for food freshness monitoring. We prepared a Vanadium-Iron Prussian blue analogue (V1/5Fe(CN)6 PBA) impregnated with insulin (INS), as a peroxidase-like mimetic probe toward 3,3'5,5'-tetramethylbenzidine (TMB) oxidation and colorimetric monitoring of fish freshness. A specific chemical reaction between putrescine as spoilage marker and the Vanadium-Iron V1/5Fe(CN)6PBA impregnated with insulin (V1/5Fe(CN)6PBA/INS) induces a decreasing peroxidase-like activity of the V1/5Fe(CN)6PBA/INS, generating lower amounts of oxidized products of TMB. The proposed bio-strategy achieved highly sensitive responses in the range of 30 nM to 12 μM toward putrescine with a detection limit of 9.0 nM and outstanding stability, reproducibility, and selectivity. The freshness of five different types of fish samples determined and produces a noticeable color change consistent with the stale fish around the 10 μM, which can warn the oldness of the fish. This new strategy of integration between peptide and multi-metal PBA with intensified enzyme-like mimetics activity may be highly meaningful for thoroughly monitoring the amount of fish freshness.