aWeight loss, grafting amount and density were calculated for each modification step, not for total modification. b Size were measured by dynamic light scattering as mono-distribution after sonication for 30-60 min. c Size was measured in H2O. d Size was measured in dimethylformamide triethylamine (DMF-TEA) (3:1). e Size was measured in DMF. g Weight loss of water from surface of bare silica particle. h Grafting amount and density of Si-OH available for modification on the surface calculated from water loss.