Double Stokes polarimetric microscopy for chiral fibrillar aggregates

Area of Science:

• Biophysics
• Optical Imaging
• Materials Science

Background:

• Second harmonic generation (SHG) microscopy visualizes non-centrosymmetric biological structures like collagen.
• Polarimetric SHG measurements offer ultrastructural insights into fibrillar organization within a voxel.
• Existing polarimetric analysis can be complex and time-consuming.

Purpose of the Study:

• To introduce a simplified, rapid method for characterizing chiral symmetry fibers using SHG microscopy.
• To develop a reduced nonlinear polarimetry technique named double Stokes polarimetry (DSP).
• To enable quick, data-fitting-free analysis of ultrastructural parameters.

Main Methods:

• Developed double Stokes polarimetry (DSP) based on double Stokes-Mueller polarimetry.
• Utilized linear and circular incident and outgoing polarization states.
• Defined analytical expressions for DSP parameters using SHG Stokes vector components and a complex chiral susceptibility (CCS) model.

Main Results:

• Derived ultrastructural parameters (chiral susceptibility ratio magnitude/phase, achiral ratio, fiber orientation) from measurable DSP parameters.
• Validated DSP with rat tail tendon samples oriented at various angles.
• Demonstrated DSP's ability to simplify and accelerate polarimetric analysis.

Conclusions:

• DSP provides a fast and simplified approach for characterizing chiral symmetry fibers without data fitting.
• The method allows for the investigation of collagen's chiral susceptibility and its modifications in disease.
• DSP is suitable for mapping ultrastructural parameters over large areas for histopathology.