A dual-color ratiometric fluorescence sensor of biogenic amines with dye encapsulated covalent organic framework for meat freshness

Developing sensitive, nondestructive and real-time methods for assessing meat freshness is vital for ensuring food safety. Traditional monochromatic fluorescent probes for monitoring meat freshness markers like biogenic amines often face challenges in sensitivity, interference, visualization and portability for practical applications. Herein, we constructed a new Ru-Flu@COF fluorescence sensor, by combining a green fluorescent dye-encapsulated covalent organic framework (Flu@COF) with a red fluorescent compound (Ru (bpy)(3)(2+)), exhibiting a dual inverse ratiometric fluorescence signal towards essential biogenic amines His and NH3<middle dot>H2O, thus achieving a rich color gradient and spoilage-sensitive color discrimination. The detection linear range for His and NH3<middle dot>H2O was 0.6-200 mu M and 0.5-60 mg/L, with limits of detection of 0.5 mu M and 0.2 mg/L, respectively. Furthermore, Ru-Flu@COF gel labels together with a smartphone enable portable, in situ and naked-eye monitoring freshness of pork, fish and shrimp, where the freshness level can be visually identified through the gel label color from red (fresh) to orange (less fresh), yellow (spoilage) and green (severe spoilage). The proposed smart label has the advantages of high sensitivity, excellent visual discrimination and portability, and it can be a promising platform for in situ nondestructive monitoring freshness of various kinds of meat for food safety inspection in the future.