Polarimetric second-harmonic generation microscopy of partially oriented fibers I: Digital modeling

Mehdi Alizadeh; Serguei Krouglov; Virginijus Barzda

doi:10.1016/j.bpj.2023.08.016

Polarimetric second-harmonic generation microscopy of partially oriented fibers I: Digital modeling

Biophys J. 2023 Oct 3;122(19):3924-3936. doi: 10.1016/j.bpj.2023.08.016. Epub 2023 Aug 22.

Authors

Mehdi Alizadeh¹, Serguei Krouglov², Virginijus Barzda³

Affiliations

¹ Laser Research Centre, Faculty of Physics, Vilnius University, Vilnius, Lithuania; Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario, Canada; Department of Physics, University of Toronto, Toronto, Ontario, Canada.
² Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario, Canada; Department of Physics, University of Toronto, Toronto, Ontario, Canada.
³ Laser Research Centre, Faculty of Physics, Vilnius University, Vilnius, Lithuania; Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario, Canada; Department of Physics, University of Toronto, Toronto, Ontario, Canada. Electronic address: virgis.barzda@utoronto.ca.

PMID: 37608550
PMCID: PMC10560684 (available on 2024-10-03)
DOI: 10.1016/j.bpj.2023.08.016

Abstract

Second-harmonic generation (SHG) in biological tissues originates predominantly from noncentrosymmetric fibrillar structures partially oriented within a focal volume (voxel) of a multiphoton excitation microscope. This study is aimed to elucidate fibrillar organization factors influencing SHG intensity, as well as achiral, R, and chiral, C, nonlinear susceptibility tensor component ratios. SHG response is calculated for various configurations of fibrils in a voxel using the digital nonlinear microscope. The R and C ratios are calculated using linear incident and outgoing polarization states that simulate polarization-in polarization-out polarimetric measurements. The investigation shows strong SHG intensity dependence on parallel/antiparallel fiber organization. The R and C ratios are strongly influenced by the fiber chirality, tilting of the fibers out of the image plane, and crossing of the fibers. The computational modeling provides the basis for the interpretation of polarimetric SHG microscopy images in terms of the ultrastructural organization of fibers in each voxel of the samples. The modeling results are employed in the accompanying paper to investigate the ultrastructures with parallel/antiparallel fibers and two-dimensional and tree-dimensional crossing fibers in biological and biomimetic structures.