Portable Fluorescence Histamine Sensor for Assessing Freshness Utilizing Hydrogel Embedded with Dual-Ligand Europium Metal–Organic Framework

Histamine is a kind of biogenic amine released in spoiled food, which can serve as a key indicator for assessing the freshness of seafood. It is important to develop some efficient methods for histamine detection. In this work, a dual-emission europium-metal–organic framework (Eu-MOF) was designed and applied to design a ratiometric fluorescence sensing strategy for histamine detection. The MOF was synthesized in one step using two ligands: 5-boronoisophthalic acid (5-BOP) and 2-hydroxyterephthalic acid (BDC-OH). Eu³⁺ was sensitized by 5-BOP through the antenna effect and exhibited red emission at 618 nm, while the BDC-OH exhibited bright blue emission at 434 nm. The MOF displayed dual-emission responses to histamine, characterized by an increase in 434 nm and a concomitant decrease at 618 nm, so the ratio of I₆₁₈/I₄₃₄ decreased with a pronounced fluorescence color shift from purple to blue. I₆₁₈/I₄₃₄ exhibited a linear range with histamine from 0 to 200 mg/L with a detection limit of 0.17 mg/L (LOD = 3σ/K_SV). The synthesized Eu-BOP/BDC-OH was integrated with carrageenan to fabricate a hydrogel composite film for portable detection of histamine, and the changing of color can be utilized for semiquantitative freshness detection. The proposed method provided a reliable and efficient portable strategy for histamine detection in seafood.