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Ratiometric Fluorescent Probes Based on Through-Bond Energy Transfer of Cyanine Donors to Near-infrared Hemicyanine Acceptors for Mitochondrial pH Detection and Monitoring of Mitophagy

Abstract

Two ratiometric near-infrared fluorescent probes (A and B) have been developed to selectively and accurately detect mitochodrial pH changes based on highly efficient through-bond energy transfer (TBET) from cyanine donors to near-infrared-emissive hemicyanine acceptors. The probes consist of identical cyanine donors connected to different hemicyanine acceptors with a spirolactam ring structure linked via a biphenyl linkage. At neutral or basic pH, the probes display only fluorescence of the cyanine donors when they were excited at 520 nm. However, acidic pH conditions trigger spirolactam ring opening leading to increased -conjugation to the hemicyanine acceptors, resulting in new near-infrared fluorescence peaks at 740 nm and 780 nm for probes A and B, respectively. This results in ratiometric fluorescence responses of the probes to pH changes indicated by decreases of the donor fluorescence and increases of the acceptor fluorescence under donor excitation at 520 nm due to a highly efficient TBET from the donors to the acceptors. The probes only show cyanine donor fluorescence in alkaline-pH mitochdria. However, the probes show moderate fluorescence decreases of the cyanine donor and considerable flurescence increases of hemicyanine acceptors during the mitophagy process induced by nutrient starvation or under drug treatment. The probes display rapid, selective, and sensitive responses to pH changes over metal ions, good membrane penetration, good photostability, large pseudo-Stokes shifts, low cytotoxicity, mitchondria-targeting, and mitophagy-tracking capabilities.

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Supplementary files

Article information


Submitted
18 Oct 2019
Accepted
10 Dec 2019
First published
11 Dec 2019

J. Mater. Chem. B, 2019, Accepted Manuscript
Article type
Paper

Ratiometric Fluorescent Probes Based on Through-Bond Energy Transfer of Cyanine Donors to Near-infrared Hemicyanine Acceptors for Mitochondrial pH Detection and Monitoring of Mitophagy

S. Xia, J. Wang, Y. Zhang, N. whisman, J. Bi, T. E. Steenwinkel, S. Wan, J. Medford, M. Tajiri, R. L. Luck, T. Werner and H. Liu, J. Mater. Chem. B, 2019, Accepted Manuscript , DOI: 10.1039/C9TB02302J

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