A Novel Light-Harvesting ZIF-9-TCPP as a Promising FRET-based Ratiometric Fluorescence Probe for Sperm Mobility

The concentration of zinc ions in semen is significantly correlated to the sperm viability and male fertility. In this work, a reliable ratiometric fluorescence probe (ZIF-9-TCPP) based on the efficient Förster resonance energy transfer (FRET) process be-tween two luminophores, benzimidazole (BIM) and meso-tetra (4-carboxyphenyl) porphyrin (TCPP) for Zn2+ detection has been constructed, where the emission of BIM and TCPP are used as reference and detection signals. The proximity of BIM and TCPP in one framework (ZIF-9-TCPP) and the overlapped spectra between BIM and TCPP afford the attainment of a highly efficient FRET (around 90% efficiency). Efficient FRET improves the fluorescence intensity of porphyrin to enhance the sensitivity of detection. The unique spectral shift resulting from Zn2+ binding to the porphyrin ring ensures the selectivity of detection. In addition, the response mechanism of the proposed ratiometric probes to Zn2+ has been investigated. This work provides a convenient way to design an efficient FRET system and a promising method for sperm mobility detection.