Biophysical Society Thematic Meeting | Tutzing 2026

Single-Molecule FRET: The Next 30 Years

Friday Speaker Abstracts

MICROTIME-GATED PHOTON STATISTICS: FROM FAST FRET DYNAMICS TO EXCITON COLLIDERS Tim Schröder 1 ; Gordon Hedley 3 ; John Lupton 2 ; Jan Vogelsang 2 ; Philip Tinnefeld 1 ; 1 Ludwig-Maximilians-Universität München, Department Chemie and Center for NanoScience (CeNS), München, Germany 2 Universität Regensburg, Institut für Experimentelle und Angewandte Physik and Regensburg Center for Ultrafast Nanoscopy (RUN), Regensburg, Germany 3 University of Glasgow, School of Chemistry, Glasgow, United Kingdom Energy transfer processes between chromophores are rarely observed directly; instead, they leave characteristic fingerprints in the photon stream. Changes in FRET-efficiency alter the fluorescence lifetime of the donor, which can be harnessed by microtime gating to turn lifetime information into a contrast variable for photon-correlation analysis. On long timescales, shrinking-gate FCS (sg-FCS) combines intensity correlations with photon arrival times after pulsed laser excitation to identify intensity fluctuations that are coupled to lifetime changes [1]. This enables quantitative kinetic analysis of two-state systems without prior knowledge of the underlying dynamics and helps to distinguish lifetime-correlated intensity changes from photophysical on-off switching. On picosecond timescales, the particle nature of light becomes evident through photon antibunching. Using picosecond time resolved photon antibunching (psTRAB), interactions between excited states can be resolved from psTRAB, revealing both the apparent number of chromophores and rates of exciton-diffusion-mediated annihilation processes [2]. I will discuss how this approach is applied to the “exciton collider”: a one-dimensional DNA-origami-based photonic containing up to nine dyes, in which excitons are injected by FRET from both ends and their encounters enhance single-photon emission through diffusion mediated singlet-singlet annihilation. Comparison with simulations allows spectral crosstalk, direct acceptor excitation, and donor photophysics to be accounted for, enabling a quantitative description of hidden excited-state dynamics encoded in the photon stream [3].References:[1] T. Schröder, J. Bohlen, S. E. Ochmann, P. Schüler, S. Krause, D. C. Lamb, P. Tinnefeld, PNAS 2023, 120, e2211896120.[2] G. J. Hedley, T. Schröder, F. Steiner, T. Eder, F. J. Hofmann, S. Bange, D. Laux, S. Höger, P. Tinnefeld, J. M. Lupton, J. Vogelsang, Nat. Commun. 2021, 12, 1327.[3] T. Schröder, P. Wutz, J. M. Lupton, P. Tinnefeld, J. Vogelsang, Small Structures 2026, 7.

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