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Proceedings Paper

In vivo phosphorescence imaging of cancer using iridium complexes
Author(s): Toshitada Yoshihara; Yasuyuki Karasawa; Shaojuan Zhang; Masahiro Hosaka; Toshiyuki Takeuchi; Yasuhiro Iida; Keigo Endo; Takashi Imamura; Seiji Tobita
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Paper Abstract

Iridium complexes exhibit highly-efficient phosphorescence that is quenched notably by ambient molecular oxygen. We utilized the oxygen-sensitive properties of the phosphorescence to visualize tumors in vivo because the levels of oxygen in tumors may be significantly below those of normal tissue. We used (btp)2Ir(acac) (BTP) as an oxygen probe because the phosphorescence of BTP appears in the red to near-infrared region and has a relatively long lifetime (5.8μs) and high quantum yield (0.32) in solution. The oxygen-quenching rate constants were determined to be 5.7 x 104 and 1.2 x 104 mmHg-1s-1 in n-hexane and in lipid bilayer of DMPC in Tris-HCl buffer solution, respectively, at 35°C. We took the phosphorescence image of HeLa cells that had been incubated under 5% and 20% O2 conditions. In 20% O2 culture condition, HeLa cells did not exhibit notable phosphorescence, while in 5% O2 culture condition, they emitted bright red phosphorescence due to BTP. Then we tested this probe to image tumors transplanted in nude mice. After 5 minutes of the BTP injection, tumor moieties began to emit red phosphorescence and after one hour each tumor was visualized very clearly by the BTP phosphorescence that could be seen only in a low oxygen state.

Paper Details

Date Published: 20 February 2009
PDF: 8 pages
Proc. SPIE 7190, Reporters, Markers, Dyes, Nanoparticles, and Molecular Probes for Biomedical Applications, 71900X (20 February 2009); doi: 10.1117/12.814494
Show Author Affiliations
Toshitada Yoshihara, Gunma Univ. (Japan)
Yasuyuki Karasawa, Gunma Univ. (Japan)
Shaojuan Zhang, Gunma Univ. (Japan)
Masahiro Hosaka, Gunma Univ. (Japan)
Toshiyuki Takeuchi, Gunma Univ. (Japan)
Yasuhiro Iida, Gunma Univ. (Japan)
Keigo Endo, Gunma Univ. (Japan)
Takashi Imamura, National Institute for Environmental Studies (Japan)
Seiji Tobita, Gunma Univ. (Japan)

Published in SPIE Proceedings Vol. 7190:
Reporters, Markers, Dyes, Nanoparticles, and Molecular Probes for Biomedical Applications
Samuel Achilefu; Ramesh Raghavachari, Editor(s)

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