For the study of biological systems such as living cells, access to oxygen concentrations in various organelles is important. In living cells, the lifetime of pyrene fluorescence can be used to measure local oxygen concentrations. We designed and synthesized a new probe to measure the oxygen concentration in mitochondria ([1'- pyrene butyl]-2-rhodamine ester, PRE). The localization of the probe was studied by videomicrofluometry in 3T3 cells and confirmed to label the mitochondria. We compared the lifetime of PRE with the well-known cytosol specific probe Pyrene Butyric Acid in (1) in living cells (2) in liposomes and (3) in solution. Liposomes were used to investigate the effect of phospholipid bilayer organization on the fluorescence lifetimes. Depending on the oxygen concentration we observed lifetime variation ranges of (1) 60 ns (hyperoxygenation) - 110 ns (anoxy) in cells (2) 60 - 220 ns in liposomes and (3) 6 - 220 ns in ethanolic solution. These results indicate that, under hyperoxygenation, quenching is less efficient in organized environments than in solution. Without oxygen and in cellular medium, the quenching depends on the composition of the probe environment. Accordingly, these probes can be used to measure the intracellular oxygen concentrations as well as changes in the environment.
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