Visualizing nanostructures in supramolecular hydrogels: a correlative study using confocal and cryogenic scanning...

Area of Science:

• Materials Science
• Nanotechnology
• Supramolecular Chemistry

Background:

• Solvated supramolecular hydrogels possess fragile fibrous structures and low solid component concentrations, complicating nanoscale morphological characterization.
• Imidazolium-based hydrogels incorporating fluorophores like diketopyrrolopyrrole (DPP) or zinc(II) phthalocyanine (ZnPc) were investigated.

Purpose of the Study:

• To compare the effectiveness of confocal laser scanning microscopy (CLSM) and cryogenic scanning electron microscopy (cryo-SEM) for characterizing supramolecular hydrogels.
• To evaluate imaging techniques for hydrogels with varying fluorescence properties and structural integrity.

Main Methods:

• Confocal laser scanning microscopy (CLSM) was used to image fully solvated gels.
• Cryogenic scanning electron microscopy (cryo-SEM) was employed to observe the corresponding xerogels (dried forms).
• DPP-containing hydrogels (DPP@Gel) and sulfonated ZnPc-containing hydrogels (ZnPc@Gel) were analyzed.

Main Results:

• DPP@Gel systems showed strong fluorescence, enabling effective CLSM imaging with morphologies correlating well with cryo-SEM observations.
• ZnPc@Gel systems exhibited weak fluorescence and sample disruption under CLSM, yielding poor images.
• Cryo-SEM successfully visualized the native fibrous network of ZnPc@Gel, overcoming CLSM limitations.

Conclusions:

• CLSM and cryo-SEM offer complementary insights into hydrogel morphology.
• Cryo-SEM is a valuable tool for imaging soft nanomaterials, especially those with low fluorescence or limited optical contrast.
• The choice of imaging technique depends on the hydrogel's specific properties, such as fluorescence intensity and structural stability.