Letter abstract
Nature Photonics 2, 44 - 47 (2008)
Published online: 9 December 2007 | doi:10.1038/nphoton.2007.251
Subject Category: Biophotonics
Firefly bioluminescence quantum yield and colour change by pH-sensitive green emission
Yoriko Ando1, Kazuki Niwa2, Nobuyuki Yamada3, Toshiteru Enomoto3, Tsutomu Irie3, Hidehiro Kubota3, Yoshihiro Ohmiya4 & Hidefumi Akiyama1
Abstract
Firefly bioluminescence1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 is the most well-known ideal photo-emitter system in biophotonics, known in particular for its extremely high quantum yield, 88 
25% (refs 2,3) or higher4, 5, 6, and its magnificent pH-dependent emission-colour change3, 7 between yellow-green and red, modelled as the chemical equilibrium between two corresponding states8, 9, 10, 11, 12, 13, 14. However, the need for re-examination has also been discussed4, 5, 6. In this letter we quantify quantum yields and colour changes using our new total-photon-flux spectrometer20, 21. We determine the highest quantum yield to be 41.0 7.4% (1 standard deviation (s.d.) estimate, coverage factor k = 1), and find that bioluminescence spectra are systematically decomposed into one pH-sensitive and two pH-insensitive gaussian components. There is no intensity conversion between yellow-green and red emissions through pH equilibrium, but simple intensity variation of the pH-sensitive gaussian peak at 2.2 eV causes the changes in emission colours. This represents a paradigm shift in the concept of colour determination from long-standing interpretation based on pH equilibrium.
- Institute for Solid State Physics, University of Tokyo, and CREST, JST, Kashiwa, Chiba 277-8581, Japan
- Research Institute for Cell Engineering, National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka 563-8577, Japan
- ATTO Corporation, Hongo, Bunkyo-ku, Tokyo 113-8425, Japan
- Department of Photobiology, Graduate School of Medicine, Hokkaido University, North 15, West 7, Kita-ku, Sapporo, Hokkaido, 060-8638, Japan
Correspondence to: Yoriko Ando1 e-mail: yori@issp.u-tokyo.ac.jp
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