Biophysical Society Thematic Meeting | Tutzing 2026

Single-Molecule FRET: The Next 30 Years

Tuesday Speaker Abstracts

THE ELECTRODYNAMICS OF FLUORESCING MOLECULES: A TRIBUTE TO KARL-HEINZ DREXHAGE Joerg Enderlein 1 ; 1 Georg August University, Third Institute of Physics (Biophysics), Göttingen, Germany Edward Purcell was the first physicist to point out that a metallic cavity alters the local density of states of the electromagnetic field [1]. This alteration changes the coupling of an electromagnetic emitter to these states, thereby modulating the lifetime of its excited state—a phenomenon known as the Purcell effect. Although originally conceptualized by Purcell for emitters in the radio frequency range, it later became clear that this effect should also be observable for light emitting sources placed within a plasmonic nanocavity or close (in the near-field range) to a surface. This prediction was spectacularly verified by the seminal experiments of Karl-Heinz Drexhage and colleagues [2–5], who measured the distance-dependent fluorescence lifetime modulation of long-lived europium complexes in front of a mirror. Since these groundbreaking experiments, the effect has found widespread applications in spectroscopy and microscopy, two of which will be discussed extensively in this presentation. After providing a brief introduction to the physics underlying the interaction between a fluorescent molecule and nano-engineered plasmonic environments, two important applications will be presented: The modulation of the mean observable fluorescence lifetime of a solution of fluorescent emitters within a plasmonic nanocavity of varying length, and its use for determining absolute fluorescence quantum yields in a calibration-free manner [6]. The modulation of the fluorescence lifetime of a single emitter as a function of its distance to a metal surface, and the use of this effect to measure the emitter to-surface distance with nanometer accuracy (Metal-Induced Energy Transfer, or MIET imaging) [7]. References [1] E. M. Purcell, Spontaneous emission probabilities at radio frequencies, Phys. Rev. 69, 681 (1946). [2] K. H. Drexhage, Influence of a dielectric interface on fluorescence decay time, J. Lumin. 1–2, 693 (1970). [3] K. H. Drexhage, Interaction of Light with Monomolecular Dye Layers, in Progress in Optics, edited by E. Wolf, Vol. 12 (Elsevier, 1974), pp. 163–232. [4] K. H. Drexhage, H. Kuhn, and F. P. Schäfer, Variation of the fluorescence decay time of a molecule in front of a mirror, Berichte Bunsenges. Für Phys. Chem. 72, 329 (1968). [5] K. H. Drexhage, Monomolecular layers and light, Sci. Am. 222, 108 (1970). [6] A. I. Chizhik, I. Gregor, B. Ernst, and J. Enderlein, Nanocavity-Based Determination of Absolute Values of Photoluminescence Quantum Yields, ChemPhysChem 14, 505 (2013). [7] A. I. Chizhik, J. Rother, I. Gregor, A. Janshoff, and J. Enderlein, Metal induced energy transfer for live cell nanoscopy, Nat. Photonics 8, 124 (2014).

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