Firefly bioluminescence quantum yield and colour change by pH-sensitive green emission

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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.

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Figure 1: Quantitative measurements of firefly bioluminescence.
Figure 2: Luminescence decay of firefly bioluminescence.
Figure 3: Gaussian fits of firefly bioluminescence.


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We thank J.W. Hastings, T. Wilson and O. Shimomura for valuable discussions and comments.

Author information

Y.A., Y.O. and H.A. conceived and designed the experiments. Y.A. and K.N. performed the experiments. Y.A., K.N., Y.O. and H.A. analysed the data. Y.A., K.N., N.Y., T.E., and H.K. contributed materials and analysis tools. Y.A. and H.A. produced the figures and wrote the paper.

Correspondence to Yoriko Ando.

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Supplementary information: discussion and figure S1 (PDF 239 kb)

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Ando, Y., Niwa, K., Yamada, N. et al. Firefly bioluminescence quantum yield and colour change by pH-sensitive green emission. Nature Photon 2, 44–47 (2008) doi:10.1038/nphoton.2007.251

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