Nose-to-Brain Translocation and Cerebral Biodegradation of Thin Graphene Oxide Nanosheets

The nose-to-brain pathway is a route by which certain materials can gain access to the central nervous system. The extent to which this happens for nanomaterials and their subsequent fate, are still being explored. Graphene oxide (GO)-based nanomaterials are yet to be explored in this context. The need to understand the interactions of GO-based materials with biological systems is critical in light of the extensive research being conducted, regarding potential applications of these materials. Such research is gradually helping to narrow the gap between bench-top research and marketed products. Herein, we characterise the extent to which precision-engineered, extensively characterised GO sheets of different controlled lateral dimensions, translocate from the nose to the brain following intranasal instillation. We explore the tissue location and in vivo biodegradability of the translocated materials. Our results, from mass spectrometry- and confocal Raman-based analysis, indicate that trace amounts of administered GO sheets underwent nose-to-brain translocation in a size-dependent manner. The smallest GO-sheet size category (ultra-small-GO, 30–500 nm) gained greatest access to the brain, in terms of quantity and brain coverage. Based on confocal Raman mapping and immunofluorescence combinations, we identified that once in the brain, us-GO sheets resided in close association with microglia, the resident macrophages of the brain. Trace quantities of us-GO within the brain were maintained over a month, but started to undergo biodegradation-related changes. This study adds to the growing awareness of the interactions and fate of graphene-based materials with biological systems.