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Sensors 2015, 15(6), 13503-13521; doi:10.3390/s150613503

Ratiometric Molecular Probes Based on Dual Emission of a Blue Fluorescent Coumarin and a Red Phosphorescent Cationic Iridium(III) Complex for Intracellular Oxygen Sensing

Department of Chemistry and Chemical Biology, Graduate School of Science and Technology, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515, Japan
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Author to whom correspondence should be addressed.
Academic Editor: Yoshiteru Ishida
Received: 27 April 2015 / Revised: 27 May 2015 / Accepted: 4 June 2015 / Published: 9 June 2015
(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Japan 2015)
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Abstract

Ratiometric molecular probes RP1 and RP2 consisting of a blue fluorescent coumarin and a red phosphorescent cationic iridium complex connected by a tetra- or octaproline linker, respectively, were designed and synthesized for sensing oxygen levels in living cells. These probes exhibited dual emission with good spectral separation in acetonitrile. The photorelaxation processes, including intramolecular energy transfer, were revealed by emission quantum yield and lifetime measurements. The ratios (RI = (Ip /If) ) between the phosphorescence (Ip) and fluorescence (If) intensities showed excellent oxygen responses; the ratio of RI under degassed and aerated conditions ( R I 0 MathType@MTEF@5@5@+= feaagKart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVCI8FfYJH8YrFfeuY=Hhbbf9v8qqaqFr0xc9pk0xbb a9q8WqFfeaY=biLkVcLq=JHqpepeea0=as0Fb9pgeaYRXxe9vr0=vr 0=vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaabaaaaaaaaape GaamOua8aadaqhaaWcbaWdbiaadMeaa8aabaWdbiaaicdaaaaaaa@38D6@ / RI) was 20.3 and 19.6 for RP1 and RP2. The introduction of the cationic Ir (III) complex improved the cellular uptake efficiency compared to that of a neutral analogue with a tetraproline linker. The emission spectra of the ratiometric probes internalized into living HeLa or MCF-7 cells could be obtained using a conventional microplate reader. The complex RP2 with an octaproline linker provided ratios comparable to the ratiometric measurements obtained using a microplate reader: the ratio of the value of RP2 under hypoxia (2.5% O2) to that under normoxia (21% O2) was 1.5 and 1.7 for HeLa and MCF-7 cells, respectively. Thus, the intracellular oxygen levels of MCF-7 cells could be imaged by ratiometric emission measurements using the complex RP2. View Full-Text
Keywords: oxygen sensor; fluorescence; phosphorescence; iridium complex; ratiometric probe; living cells; imaging oxygen sensor; fluorescence; phosphorescence; iridium complex; ratiometric probe; living cells; imaging
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Yoshihara, T.; Murayama, S.; Tobita, S. Ratiometric Molecular Probes Based on Dual Emission of a Blue Fluorescent Coumarin and a Red Phosphorescent Cationic Iridium(III) Complex for Intracellular Oxygen Sensing. Sensors 2015, 15, 13503-13521.

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