S1a1-a2, Fig. ). The non-porous SNS has a smooth surface and is spherical with a diameter of ∼200 nm (Fig. ). Dynamic light scattering (DLS) analysis shows that the hydrodynamic diameters of SNS, DFNS-4 and DFNS-20 were 249.4, 468.6 and 242.4 nm, respectively (Table ). The BET surface areas of DFNS-4, DFNS-20 and SNS were 460.6, 783.5 and 16.7 m 2 /g, respectively (Fig. , b3, c3 and Table ). The pore size of DFNS-4, calculated from the desorption isotherm using the BJH method, was 4 nm. The size of the predominant pores in DFNS-20 was found to be 20 nm (Fig. , b4 and Table ). After coating PDA on the surface of the nanoslica for 16 h, the BET surface areas of DFNS-4@DA, DFNS-20@DA and SNS@DA changed to 20.5, 359 and 2.41 m 2 /g, respectively (Fig. , b3, c3 and Table ). The mesopores in DFNS-4@DA was therefore filled up with the PDA polymer, and the predominant mesopores in DFNS-20@DA became smaller (15 nm) after coating with PDA (Fig. , b1 and Table ). As revealed by the SEM and TEM images (Fig. a1-a2 and b1-b2), DFNS-4@DA and DFNS-20@DA have no obvious change in particle sizes after coating with PDA, suggesting that the PDA was coated predominantly on the inner surface of the mesopores. For SNS@DA, the particle surface became rougher due to the attachment of the PDA layer on the core particles (Fig. ). The TGA results reveal that the mass ratio of PDA in SNS@DA, DFNS-4@DA and DFNS-20@DA were 26.7 %, 25.4 % and 23.4 %, respectively (Fig. , b2, c2 and Table ), indicating the successful synthesis of PDA layer on the nanosilica surfaces. The amount of PDA formed on the non-porous silica nanoparticles was slightly higher than on the mesoporous particles. DLS analysis reveals that the hydrodynamic diameters of SNS@DA, DFNS-4@DA and DFNS-20@DA were 262.2, 473.5 and 252.4 nm, respectively (Fig. and Table ).