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,
described in our previous published work [38], were applied. Brief explanations are given in the following paragraph.
Bare silica NPs were synthesized by one-pot/one-step sol-gel method. A solution containing 0.25 mol/L TEOS in 200 ml
EtOH was prepared by vigorously stirring at 65 C under nitrogen atmosphere. After 5 min, NH4OH and H2O were added.
The final solution was centrifuged at 12,000 rpm for 10 min and then rinsed by DI water and ethanol for several times to
ensure the removal of unreacted materials. The particles were dried at 75 C for 24 h to obtain the final NPs.