The　modular　nature　of　metal-organic　frameworks　(MOFs)　permits　their　tunable　structure　and　function　for　target　application,　such　as　in　biomedicine.　Herein,　a　green-emission　Zr(IV)-MOF　(BUT-88)　was　constructed　from　a　customized　luminescent　carbazolyl　ligand.　BUT-88　represents　the　first　bcu-type　MOF　with　both　organic　linker　and　metal　node　in　eight　connections　and　shows　medium-sized　pores,　rich　accessible　linking　sites,　and　good　water　stability　and　biocompatibility.　In　virtue　of　these　merits,　BUT-88　was　then　fabricated　into　a　MOF-based　fluorescent　nanoprobe,　drDNA-BUT-88.　Using　it,　the　live-cell　imaging　of　dual　tumor　biomarkers　was　achieved　for　the　first　time　upon　a　MOF-based　probe,　offering　enhanced　detection　precision　in　early　cancer　diagnosis.　Particularly,　the　probe　showed　efficient　ratiometric　fluorescent　sensing　toward　the　cytoplasmic　biomarker　microRNA-21,　further　improving　the　detection　accuracy　at　the　cellular　level.　In　this　work,　the　elaborate　combination　of　MOF　engineering　and　the　fluorescent　detection　technique　has　contributed　a　facile　biosensing　platform,　unlocking　more　possibilities　of　MOF　chemistry.