[Optical Second-harmonic Observation of Stimulated Sacran Aggregates]

Area of Science:

• Nonlinear Optics
• Materials Science
• Biophysics

Background:

• Sacran is an ampholytic megamolecular polysaccharide with potential applications.
• Understanding the aggregation behavior of sacran is crucial for its material properties.
• Nonlinear optical microscopy offers insights into molecular organization.

Purpose of the Study:

• To investigate the aggregation structures of sacran under various stimuli.
• To characterize the molecular orientation within sacran aggregates.
• To explore the influence of external factors on sacran aggregation.

Main Methods:

• Optical second-harmonic generation (SHG) microscopy was employed.
• SHG imaging was performed on sacran cotton-like lumps and fibers.
• Sacran was studied in a needle-ring electrode setup with applied voltage.
• SHG signals near cast film edges were also analyzed.

Main Results:

• SHG microscopy revealed microspots of organized sacran molecules in concentric multilayers.
• Clear incident polarization dependence was observed in the SHG signals.
• SHG intensity was enhanced near a negatively biased needle electrode.
• SHG signals at cast film edges suggested phase-separation structures.

Conclusions:

• Sacran molecules exhibit diverse aggregation patterns.
• Molecular orientation and organization are stimulus-dependent.
• SHG microscopy is effective for visualizing sacran's supramolecular structures.