Multifunctional Nanoscale\nMetal–Organic Layers\nfor Ratiometric pH and Oxygen Sensing

Abstract

As a monolayered version of nanoscale metal–organic\nframeworks\n(nMOFs), nanoscale metal–organic layers (nMOLs) represent an\nemerging class of highly tunable two-dimensional materials for hierarchical\nfunctionalization and with facile access to analytes. Here we report\nthe design of the first nMOL-based biosensor for ratiometric pH and\noxygen sensing in mitochondria. Cationic Hf₁₂-Ru nMOL was\nsolvothermally synthesized by laterally connecting Hf₁₂ secondary building units (SBUs) with oxygen-sensitive Ru­(bpy)₃²⁺-derived DBB-Ru ligands (bpy = 2,2′-bipyridine).\nThe Hf₁₂-Ru nMOL was then covalently functionalized with\npH-sensitive fluorescein isothiocyanate and pH/oxygen-independent\nRhodamine-B isothiocyanate through thiourea linkages to afford Hf₁₂-Ru-F/R as a mitochondria-targeted ratiometric sensor for\npH and O₂ in live cells. High-resolution confocal microscope\nimaging with Hf₁₂-Ru-F/R revealed a positive correlation\nbetween pH and local O₂ concentration in mitochondria.\nOur work shows the potential of nMOL-based ratiometric biosensors\nin sensing and imaging of biologically important analytes in live\ncells.