Electrophoretic mobility (µ) was measured using a ZetaSizer Nano ZS (Malvern Instruments, UK) after dilution of GO with water to a concentration 20 µg/mL, in disposable ZetaSizer cuvettes (Malvern Instruments, UK). Default settings and automatic analysis were used for all measurements, where the µ value was converted automatically by the equipment software to zeta potential (ζ) values according to Henry's equation. Each measurement was performed in triplicate at room temperature and values were reported as mean ± SD.