HMSNs characterization

The morphology and structure of HMSNs were determined by using scanning electron microscope (SEM; Sirion 200) and transmission electron microscope (TEM; Tecnai, G220). For SEM sample preparation, a dilute aqueous solution of the nanoparticles (2.5 mg/mL) was suspended adequately and then dropped on a clean silicon wafer and dried thoroughly. Then, a layer of gold was sprayed on the surface of nanoparticles for observation. Before TEM observation, the samples were dispersed in very dilute water (0.5 mg/mL) by sonication and then deposited on copper grids. Then, the as-prepared grids were dried completely at room temperature.

The diameter and zeta potential of the HMSNs and Tf-HMSNs were measured using a dynamic light scattering (DLS) apparatus. All the samples were prepared by ultrasonic dispersing.

Surface area and pore size of HMSNs were measured using surface area and porosity analyzer (NOVA 3200e). The nitrogen adsorption–desorption isotherm was detected at −196°C. The surface areas were calculated by Brunauer–Emmett– Teller (BET) method at the pressure range of 0.05–0.2. Adsorption data were collected for pore size distribution calculate by Barrett–Joyner–Halenda (BJH) method.