By using biocompatible luminescent single wall carbon nanotubes (SWCNTs) in the near-IR emission [2,3], here we show an approach to directly observe local structures and rheology of the extracellular space in a brain tissue using super-resolution imaging. Upon injection in live rat cerebroventricles , individual SWCNTs are followed for tens of minutes in acute slices as they diffuse inside the extracellular space. Because of the interplay between the nanotube geometry and the extracellular space local environment , we can extract information about the extracellular space dimension and local viscosity. We find a striking diversity of extracellular space dimensions down to 40 nm, and as well as of local viscosity values. Moreover, by chemically altering the brain extracellular matrix of the live animals before nanotube injection, we reveal that ECS rheology properties are affected, but that extracellular space alterations are local and inhomogeneous at nanoscale dimensions .
 Godin et al , Biophys. J, (2014).
 Gao, et al, Biomater. Sci.(2016).
 Danné et al submitted
 Varela et al Nat. Comm. (2016).
 Fakhri et al , Science(2010).
 Godin et al Nat. Nanotechnol. (2016).