Novel Method To Investigate the Interaction Force between Etoposide and APTES-Functionalized Fe3O4@nSiO2@mSiO2 Nanocarrier for Drug Loading and Release Processes

We report a 3-aminopropyltriethoxysilane (APTES) functionalized magnetic core–shell structure drug delivery system which is composed of a nonmesporous silica (nSiO 2 ) coated Fe 3 O 4 nanoparticle as the core and mesoporous silica (mSiO 2 ) as the shell (designated Fe 3 O 4 @nSiO 2 @mSiO 2 -APTES). These spheres have superparamagnetism, high magnetization (39.1 emu/g), a large surface area (222.35 m 2 /g), uniform accessible mesopores (2.5 nm), and abundant amino groups on the mesoporous shell. We investigated the thermodynamic and kinetic properties for the drug loading and release processes using microcalorimetry for the first time. The drug loading process was exothermal, and the release process was endothermal. A series of thermodynamics parameters Δ H, Δ S, and Δ G for drug loading and release processes was calculated. For drug loading process, the critical value was determined, the kinetics equation d α /d t = 10 –3.66 (1 – a ) 1.01, and rate constant k = 10 –3.66 s –1 was also obtained. The results show that the interaction between the drug molecule and the nanocarrier is a hydrogen-bond interaction which was derived from the experimental values of the molar enthalpies (Δ H < 0) and molar entropy (Δ S < 0). This method therefore promise to provide a theoretical basis for the interaction between the drug molecule and the nanocarrier, so as to guide an externally controlled drug-delivery system in cancer therapy.