Grids were glow-discharged before use. 5 μL of nanoparticle suspensions were deposited for 30 s on copper grids covered with formvar-carbon film. The excess solution was blotted off using a filter paper. Samples were then stained using uranyl acetate (2 %, w/v) for 1 min at room temperature. Then the excess solution was removed using a filter paper. The grids were then analyzed using a JEOL JEM-1400 operating at 80 kV. Images were acquired using an Orius camera (Gatan Inc, USA). The nanoparticles were analyzed by defining the numberaverage diameter (d n ), the weight-average diameter (d w ), the z-average diameter (d z ) and the polydispersity index (PDI) using the following equations: