Raman spectroscopy as a tool to evaluate brain tissue composition after administration of reduced graphene oxide

Recently, we demonstrated that reduced graphene oxide (rGO) induces transient opening of the blood–brain barrier. When rGO was injected systemically in rats, we observed downregulation in the expression of hippocampal proteins responsible for maintaining paracellular tightness, which suggested weakening of the blood-brain barrier. In addition, analysis of the spatial distribution of rGO by matrix-assisted laser desorption/ionization mass spectrometry imaging and the determination of anatomical, cellular, and molecular parameters suggested that rGO had gained access to the brain. However, it remained unclear whether these events could result in alterations to the molecular homeostasis of the brain. To address this issue, in this study we used Raman spectroscopy and the same rat model and experimental design of the previous study to investigate rGO-provoked molecular changes in the hippocampus. Systemically injected rGO caused a time-dependent reduction in the relative intensity of the Raman bands related to protein and lipid content. Transmission electron microscopy showed alterations in neuronal nuclear membranes and chromatin patterns that could be explained by the Raman spectral alterations. All alterations were reversible and were no longer prominent seven days after rGO administration. We conclude that Raman spectroscopy can be an important complementary technique for monitoring the molecular effects induced by nanomaterials.8380581