The characterisation pipeline used here to study the physicochemical properties of GO flakes allowed the meticulous assessment of their lateral size, thickness, surface chemistry, colloidal stability and endotoxin contamination. A similar strategy has been recently applied to the observation of graphene oxide sheets using similar microscopic techniques to our study . Our proposed systematic approach is expanded to cover the surface chemistry of GO, which will affect many of the desired properties of GBMs in industry and will determine the definition of Health and Safety standards .