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It is an important task to real-time monitor biogenic amines (BAs) released from perishable seafood for predicting their freshness. To this endeavor, herein we developed a simple and effective strategy for visual determination of BAs by dual-emissive metal-organic framework (MOF) probes and color-transition hydrogels. Through situ encapsulating Ru(bpy) 3 2+ into UiO-OH, the functionalized Ru@UiO-OH was solvothermally prepared. At a single excitation wavelength, the fluorescence intensity of Ru@UiO-OH at 537 and 600 nm showed different changes in the case of trimethylamine (TMA), leading to a ratiometric platform with apparent color variation from orange red to bright yellow. The achieved turn-on yellow emission resulted from the inhibition of LMCT and ESIPT process caused by MOF skeleton damage and deprotonation. Intelligently, Ru@UiO-OH was loaded into hydrogels that acted as "sniffing" trademarks to detect volatile TMA vapor, which was further integrated with a smartphone-based readout to quantify. Meanwhile, the practical applicability of fluorescent sensory hydrogels was confirmed via depicting the spoilage degree of shrimp and fish at 4 and 20 ℃, the results were good consistent with standard method for detection of total volatile basic nitrogen (TVB-N). The current creation holds great significance for precise guidance of sensing seafood freshness with straightforward manner. [Display omitted] • Dual-emitting Ru@UiO-OH has been solvothermally prepared by situ encapsulation. • The red-emission acted as a reference, overcoming the interference of environment. • Hydrogel-based "sniffing" sensing platform with color transition was constructed. • The hydrogel label successfully described the spoilage degree of shrimp and fish. [ABSTRACT FROM AUTHOR]