Experimental validation of a theoretical model of dual wavelength photoacoustic (PA) excitation in fluorophores

Julia Märk; Christoph Theiss; Franz-Josef Schmitt; Jan Laufer

doi:10.1117/12.2082613

11 March 2015 Experimental validation of a theoretical model of dual wavelength photoacoustic (PA) excitation in fluorophores

Julia Märk, Christoph Theiss, Franz-Josef Schmitt, Jan Laufer

Author Affiliations +

Proceedings Volume 9323, Photons Plus Ultrasound: Imaging and Sensing 2015; 93233G (2015) https://doi.org/10.1117/12.2082613
Event: SPIE BiOS, 2015, San Francisco, California, United States

Abstract

Fluorophores, such as exogenous dyes and genetically expressed proteins, exhibit radiative relaxation with long excited state lifetimes. This can be exploited for PA detection based on dual wavelength excitation using pump and probe wavelengths that coincide with the absorption and emission spectra, respectively. While the pump pulse raises the fluorophore to a long-lived excited state, simultaneous illumination with the probe pulse reduces the excited state lifetime due to stimulated emission (SE).This leads to a change in thermalized energy, and hence PA signal amplitude, compared to single wavelength illumination. By introducing a time delay between pump and probe pulses, the change in PA amplitude can be modulated. Since the effect is not observed in endogenous chromophores, it provides a contrast mechanism for the detection of fluorophores via PA difference imaging. In this study, a theoretical model of the PA signal generation in fluorophores was developed and experimentally validated. The model is based on a system of coupled rate equations, which describe the spatial and temporal changes in the population of the molecular energy levels of a fluorophore as a function of pump-probe energy and concentration. This allows the prediction of the thermalized energy distribution, and hence the time-resolved PA signal amplitude. The model was validated by comparing its predictions to PA signals measured in solutions of rhodamine 6G, a well-known laser dye, and Atto680, a NIR fluorophore.

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Julia Märk, Christoph Theiss, Franz-Josef Schmitt, and Jan Laufer "Experimental validation of a theoretical model of dual wavelength photoacoustic (PA) excitation in fluorophores", Proc. SPIE 9323, Photons Plus Ultrasound: Imaging and Sensing 2015, 93233G (11 March 2015); https://doi.org/10.1117/12.2082613

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