Bare and modified silica NPs were synthesized via three different procedures. In all experiments the concentration of
TEOS as the precursor of NPs synthesis, the molar ratio of H2O/TEOS and ammonia concentration were kept constant in
0.25 mol/L, 38 and 0.5 mol/L, respectively. In order to synthesize the bare and PEG grafted silica NPs, similar procedures,