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

Abstract

Solvated supramolecular hydrogels present unique challenges in nanoscale morphological characterization because of their fragile</p><p>fibrous nature and low concentration of the solid component. In this study, imidazolium-based hydrogels containing either diketopyrrolopyrrole</p><p>(DPP) or zinc(II) phthalocyanine (ZnPc) fluorophores were imaged using confocal laser scanning microscopy</p><p>(CLSM) of fully solvated gels and cryogenic scanning electron microscopy (cryo-SEM) was used to observe the corresponding</p><p>xerogels. The DPP@Gel systems exhibit strong fluorescence and are effectively imaged using CLSM, with fibre morphologies that</p><p>closely correlate with those seen with cryo-SEM. In contrast, the analogous imidazolium gel system containing a sulfonated zinc</p><p>phthalocyanine (ZnPc@Gel) yields poor CLSM images because of the relatively weak emission and sample disruption during</p><p>compression, whereas cryo-SEM enables clear visualization of the native fibrous network. These results demonstrate the complementary</p><p>nature of CLSM and cryo-SEM and highlight the value of cryo-SEM as a very useful tool for imaging soft nanomaterials</p><p>with low fluorescence or limited optical contrast.