Abstract

Fluorescence lifetime in heterogeneous multiple light scattering systems is analyzed by an algorithm without solving the diffusion or radiative transfer equations. The algorithm assumes that the optical properties of medium are constant in the excitation and emission wavelength regions. If the assumption is correct and the fluorophore is a single species, the fluorescence lifetime can be determined by a set of measurements of temporal point-spread function of the excitation light and fluorescence at two different concentrations of the fluorophore. This method is not dependent on the heterogeneity of the optical properties of the medium as well as the geometry of the excitation–detection on an arbitrary shape of the sample. The algorithm was validated by an indocyanine green fluorescence in phantom measurements and demonstrated by an in vivo measurement.

Highlights

  • The fluorescence of the organic molecules, proteins, and nanoparticles is usually sensitive to environment through nonradiative decay process.[1,2]

  • The Monte Carlo (MC) simulation shows the result with null separation between the source and detector and the results indicate that the equality is maintained except at the shallow object depth

  • We have demonstrated a fluorescence lifetime measurement method in multiple scattering system

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Summary

Introduction

The fluorescence of the organic molecules, proteins, and nanoparticles is usually sensitive to environment through nonradiative decay process.[1,2] Many applications in biology are using fluorescence probes, which are designed or have intrinsic characters to change their fluorescence properties, in most case through the nonradiative decay pathways, by the environmental changes.[3,4,5] In some cases, the autofluorescence of biological sample reports the environmental change through such mechanism and is very useful in the actual clinical purpose.[6,7,8]The fluorescence intensity measurements have been widely used in bio- and medical sciences. The intensity-based fluorescence techniques do not yield absolute quantities and always require a reference to quantify the fluorescence. Lifetime measurements either by the time-domain or the frequency-domain technique is an absolute method to measure the fluorescence decay function and can sensitively monitor the fluorophore environment change. This technique is more robust because the artifact due to the contamination, which is generally difficult to eliminate, is more distinguished on the time axis or the phase/amplitude space and many other problems in the intensity measurements do not directly contaminate the data

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