Nanoscale\nMetal–Organic Frameworks for Real-Time\nIntracellular pH Sensing in Live Cells

Abstract

Real-time measurement\nof intracellular pH in live cells is of great\nimportance for understanding physiological/pathological processes\nand developing intracellular drug delivery systems. We report here\nthe first use of nanoscale metal–organic frameworks (NMOFs)\nfor intracellular pH sensing in live cells. Fluorescein isothiocyanate\n(FITC) was covalently conjugated to a UiO NMOF to afford F-UiO NMOFs\nwith exceptionally high FITC loadings, efficient fluorescence, and\nexcellent ratiometric pH-sensing properties. Upon rapid and efficient\nendocytosis, F-UiO remained structurally intact inside endosomes.\nLive cell imaging studies revealed endo- and exocytosis of F-UiO and\nendosome acidification in real time. Fluorescently labeled NMOFs thus\nrepresent a new class of nanosensors for intracellular pH sensing\nand provide an excellent tool for studying NMOF–cell interactions.