A Fluorescence/Colorimetric Synergistic-Enhanced Type-I Heterostructured MOF@QDs for Both Multi-Depth Food-Freshness...

Spoiled food has significantly impacted the global economy and public health, which increases worldwide concern about monitoring and preserving food freshness. Herein, a multi-functional type-I heterojunction (Eu@ZMC) is designed by europium metal-organic framework (EuMOF), zinc oxide quantum dots (ZnO QDs), and chlorogenic acid (CGA). Eu@ZMC achieves ratiometric fluorescent/colorimetric sensing of pH and biogenic amines to detect freshness. Besides, a paper-based platform (PEu@ZMC) is prepared and can detect histamine with the LOD of 0.0142 and 0.0136 µg mL^-1 in fluorescent and colorimetric modes, respectively. An advanced OR/NOT-gate logic device is further constructed to distinguish freshness into three levels (fresh, less fresh, and spoiled). This dual-mode sensor is synergistic-enhanced by the energy transfer triggered by ZnO QDs-promoted colorimetry and the type-I heterostructure of fluorescent EuMOF and ZnO QDs. The release of low-toxic zinc ions inhibits various bacterial growth, including Salmonella typhimurium. According to raw fish evaluation, Eu@ZMC not only effectively monitors spoilage externally and internally aligning with a commercial kit, but also reduces spoilage speed, which cannot be achieved through the classical detection strategy. This original work provides a simple, convenient, and reliable method for multi-depth and real-time visual food monitoring with extract freshness preservation, contributing to economic benefits and human health assurance.