Optical scattering depolarization in a biomedium with anisotropic biomolecules

The depolarization property of a biomedium with anisotropic biomolecule optical scattering is investigated theoretically. By using a simple ellipsoid model of a single biomolecule, the scattering fields and Mueller matrices are derived from fundamental electromagnetism theory. The biomedium is modeled as a system of uncorrelated anisotropic molecules. On the basis of a statistical model of anisotropic molecular distribution, the scattering depolarization of the biomedium is investigated. Simulated results of the molecular shape and orientation dependent single scattering depolarization D(1) and the double scattering depolarization D(2) are reported. The D(2) contribution is found to be more important for higher-density scattering media. The depolarizations of the forward single and double scattering of a model cell membrane are simulated and discussed. The fitting to a single tetra-methylrhodamine-labeled lipid molecule's anisotropic imaging experiment has demonstrated that large depolarization arises for the membrane to which the fluorescence emitting molecule is attached. This theory can provide a simulation analysis tool for investigating the scattering polarization/depolarization effect and the photon density wave transport property of a highly scattering biomedium.