Recent progress of crystalline porous organic frameworks as ratiometric fluorescence biosensing platforms

The abnormal concentration of biological species is closely related to some physiological symptoms or diseases, and detecting these biological species is of great significance in clinical diagnosis and clinic treatment. Hence, the design and construction of high-performance biosensor have attracted lots of attention in recent decades. Due to the low cost, feasible operation, and other advantages, luminescence probes have been regarded as one of the effective and promising strategies for detecting biological species. Compared with single-emission luminescence probes, the ratiometric fluorescence probe shows self-calibration ability and hence possesses much better antijamming capability against the unstable light source, changeable concentration of probe material, experimental errors and so on. As for optimizing the detection performance, the key factor is the selection of probe materials to construct the ratiometric fluorescence biosensors. As the popular crystalline porous frameworks, metal-organic frameworks (MOF) and covalent organic frameworks (COF) possess diverse crystalline structures and adjustable luminescence properties, which realize the collection of analytes and adjustable luminescence emission. Hence, the MOF or COF based materials possess huge potential in practical applications for luminescence probes, and the corresponding ratiometric fluorescence probes have been developed a lot. Herein, we systematically review the constructing strategy, detecting mechanism, sensing applications (i.g., biomolecules, biomarkers, drugs and others) for the MOF or COF based ratiometric fluorescence biosensing probes. In addition, the valuable references are provided for developing MOF or COF based ratiometric fluorescence probes to cater the requirements of environment monitoring and clinical diagnosis.