The three materials displayed very distinct lateral dimensions, whose distributions span across less than an order of magnitude for each one of them (Figure ). Therefore, in order to cover appropriately the range of expected flake size for each sample, an adequate selection of imaging techniques (e.g. optical microscopy, AFM or TEM) must be made. Because it covered the widest range of flakes in our study (Figure ), we conclude that electron microscopy (i.e. TEM or SEM) should be the technique of choice to assess the structural morphology of GBMs. However, the number of detected flakes must be high enough to provide a powerful statistical comparison of lateral dimensions. Optical microscopy appeared as the most convenient technique to observe large flakes such as in l-GO but lacked the resolution to accurately assess the size of small flakes typically found in s-GO and us-GO due to the Abbe's law diffraction limit. Hence, it can be readily used for the quality control of the impact of sonication on visible micrometre-sized flakes, yielding invisible nanometresized flakes under the optical microscope (Figure ). Although AFM had a more limited detection of larger GO flakes and is characterised by a low throughput, it also provides invaluable information on the thickness of GBMs (Figure ). Here, all three GO materials were made of a majority of flakes with thickness between 1 and 4 nm, corresponding to single-to few-layer flakes . Individual GO sheets have indeed been reported to have a thickness of about 1 nm, which is slightly thicker than pristine graphene due to the presence of oxygen groups and adsorbed water onto the carbon lattice .