Figure 1.

Characterization of magnetite and silanized nanoparticles. (A) X-ray diffraction (XRD) patterns of magnetite nanoparticles obtained by (red) coprecipitation and (black) thermal decomposition techniques, and (blue) after silanization. The nanoparticles exhibit and inversed spinel crystalline structured, which is translated into a fd3m spinel-type after silanization with APTES. (B) Fourier Transform infrared (FT-IR) analysis of the reaction steps for the functionalization of the magnetite nanoparticles. (blue) Magnetite nanoparticles, (red) silanized nanoparticles, (black) PEGylated nanoparticles and (yellow) bifunctional nanoparticles. Bands at 3415 cm⁻¹ and 960 cm⁻¹ correspond to the stretching and bending of the O–H bond at the surface of the nanoparticles. Bands at 1633 cm⁻¹ and 580 cm⁻¹ correlate with the bending of the H–O–H and the vibration of the Fe–O bond, respectively. The stretching of the Si–O–Si bond is identified in the 1010 cm⁻¹ band that appears after silanization. The stretching of the amide C = O bond is observed with the appearance of a new peak around 1741 cm⁻¹ after PEGylation. CH stretches of the heteroaromatic ortho-pyridyl ring appear at 2800 cm⁻¹ in the bifunctional nanoparticles. (C) Thermogravimetric analysis (TGA) of silanized nanoparticles. Three weight loss steps are identified in the graph and are attributed as follows: weight loss step at 100 °C to water loss, weight loss step at 200 °C to physically absorbed APTES, and weight loss step at 701 °C to silanized APTES species. (D, E) Hydrodynamic diameter of silanized nanoparticles obtained by (D) dynamic light scattering (DLS) and (E) small-angle X-ray scattering (SAXS) techniques. In (E), the red curve corresponds to experimental data, while the blue curve to a theoretical Gaussian approximation. (F) Raman spectroscopy of the magnetic nanoparticles. Magnetite composition is identified due to the appearance of the four phonon bands at room temperature. T_2g, A_1g and E_g modes are identified in accordance with the quasi-molecular description of the spinel tetrahedron. (G) Chemical structure of the PEGylated conjugate after immobilization of siRNA.