A lifetime in fluorescence: its measurement and application

Among all the parameters that can be used to characterise fluorescence it is the excited state lifetime which has proved to be the most informative in research.

As fluorescence started to emerge as a major molecular research technique in the 1960s and 1970s the fluorescence quantum yield and lifetime were on a par for attention as researchers sought to use them to determine fluorescence rate parameters [1]. However, the difficulties of quantum yield measurement, as compared to the higher precision and ease of measuring lifetimes, soon lead to the latter becoming the approach of choice. The emergence of lifetimes was accelerated when on-line data analysis became available and when fluorescence started to be applied to biological systems in their native state, which fortunately eliminated the need to remove oxygen and the associated quenching of fluorescence. The dominance of lifetimes was secured when the digital advantages of time-correlated single-photon counting (TCSPC) became widely-recognised and semiconductor lasers and diodes [2] offered a more reliable alternative to flashlamp sources [3].

In this talk I will describe the fundamentals and importance of fluorescence lifetime measurements in molecular spectroscopy using TCSPC, and illustrate its application to some of the most pressing healthcare needs of our age including Alzheimer’s, cancer, and diabetes [4].

References

1. J.B. Birks, Photophysics of Aromatic Molecules (Wiley-Interscience, London, 1970).

2. Coaxial nanosecond flashlamp. D.J.S. Birch and R.E. Imhof,Rev. Sci. Instrum.52,1206, 1981.

3. A new sub-nanosecond LED at 280 nm: application to protein fluorescence. C.D. McGuiness, K. Sagoo, D McLoskey and D.J.S.Birch. Meas. Sci. Technol. 15, L19, 2004.

4. Fluorescence. D.J.S. Birch, Y.Chen and O.J. Rolinski. “Biological and Medical Photonics, Spectroscopy and Microscopy.” Ed D L Andrews. Vol 4 “Photonics.” Wiley. Ch.1. 1-58, 2015.