Linear Extrapolation of the Analyte-Specific Light Scattering and Fluorescence Depolarization in Turbid Samples

Anisotropy and depolarization are two interconvertible parameters in fluorescence and light scattering spectroscopy that describe the polarization distribution of emitted and scattered photons generated with linearly polarized excitation light. Whereas anisotropy is more frequently used in fluorescence literature for studying association/dissociation of fluorophore-bearing reagents, depolarization is more popular in the light-scattering literature for investigating the effect of scatterers' geometries and chemical compositions. Presented herein is a combined computational and experimental study of the scattering and fluorescence depolarization enhancement induced by light scattering in turbid samples. The most important finding is that sample light scattering and fluorescence depolarization increases linearly with sample light-scattering extinction. Therefore, one can extrapolate the analyte-specific scattering and fluorescence depolarization through linear curve fitting of the sample light scattering and fluorescence depolarization as a function of the sample concentration or the path length of the sampling cuvettes. An example application of this linear extrapolation method is demonstrated for quantifying the fluorophore-specific fluorescence depolarization and consequently its anisotropy for an aggregation-induced-emission sample. This work should be important for a wide range of macromolecular, supramolecular, and nanoscale fluorescent materials that are often strong light scatterers due to their large sizes.