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 with 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 between two luminophores, benzimidazole (BIM) and meso-tetra (4-carboxyphenyl) porphyrin (TCPP) for Zn²⁺ detection has been constructed, where the emissions 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.