Long-term study of physicochemical stability, microbial contamination, and endotoxin levels in UVC-photoreactor sterilized graphene-based materials

The stability of UVC-Photoreactor sterilized nanographene oxide (GOn) and partially reduced graphene oxide (p-rGOn) was studied over 12 months (M), when stored at room temperature (RT), 4 °C, and -20 °C. The photoreactor used, was for the first time reported for GBM sterilization. GOn and p-rGOn dispersions maintained at 4°C and -20°C remained sterile throughout the 12M. In contrast, dispersions of both materials stored at RT exhibited bacterial, fungal, and endotoxin contamination after 12M. GOn water dispersions remained visually stable for 12M in all storage conditions. However, the water stability of p-rGOn kept at RT was visually decreased after 8M, when at 4 °C it decreased after 12M, while at -20 °C no changes were observed. Moreover, materials stored at -20 °C could be defrosted and redispersed by bath ultrasonication (30 min), keeping original properties and sterility. Both materials presented lateral average sizes ranging around 100-130 nm, which remained consistent for 12M in all storage conditions, also their physicochemical properties were stable. For the first time, sterile GBM stability was systematically evaluated for 12M, which provided important insights into long-term storage conditions, relevant for commercialization, shipping, and assurance of sterility for biomedical grade applications, among others.