Short peptide based hydrogels: incorporation of graphene into the hydrogel

Stable supramolecular hydrogels were obtained from Fmoc (N-fluorenyl-9-methoxycarbonyl) protected synthetic dipeptides, Fmoc-Xaa-Asp-OH (Xaa = Tyr, Phe). These hydrogels were characterized by various methods including transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), fluorescence spectroscopy and rheology. Different microscopic studies showed the presence of an entangled uniform nanofibrillar network structure in the gel state. These gelator molecules containing aromatic moieties in the side chain (Tyr/Phe) and in the N-terminus (fluorenyl group) can be useful in interacting with graphene sheets using p-p stacking interactions. One of these peptide based hydrogels (Fmoc-Tyr-Asp-OH) was utilized for the successful incorporation of reduced graphene oxide (RGO) into the hydrogel to make a well-dispersed RGO containing stable hybrid hydrogel. This study demonstrates that RGO is stabilized within the peptide based hydrogel system without the help of any external stabilizing agent. The RGO containing hybrid hydrogel was characterized using transmission electron microscopy, selected area electron diffraction, atomic force microscopy, Raman spectroscopy, and rheology. Morphological studies reveal the presence of a nano-hybrid system containing graphene (RGO) sheets and gel nanofibrils. The morphology of the peptide hydrogel does not change significantly even after the incorporation of RGO as it is evident from TEM and AFM studies. Rheological studies suggest the formation of a more rigid and 'solid-like' hybrid hydrogel after the incorporation of RGO into the native hydrogel.