Small GO flakes (s-GO) were produced from reconstituted l-GO dispersion by exposing aliquots that were dispensed to depyrogenated and autoclaved glass vials to a water bath sonicator (VWR, UK) operating at 80 W (45 kHz) for 5 min. The dispersion was then centrifuged at 13000 rpm for 5 min in order to remove the remaining l-GO flakes. Ultrasmall GO flakes (us-GO) were produced from the l-GO dispersion and were processed in a similar manner, adjusting the sonication time to 4 h and the centrifugation time to 1 h. In this latter case, the water level in the sonication bath was regularly adjusted and its temperature carefully monitored so that it did not exceed 40ºC; the water bath was replaced approximately every hour. The concentration of these 2 materials was also determined by comparing the sample weight before and after freeze-drying 20 mL of each dispersion.