Magnetic hollow silica nanotubes for bio-applications

In this paper, a novel synthetic route is reported for magnetic silica nanotubes (MSNTS) via a sol-gel method by using nanosized calcium carbonate (CaCO₃) nanoneedle as a sacrificial template, and Fe₃O₄ nanoparticle and tetraethoxysilane (TEOS) as precursors. The samples were investigated by field scanning electron microscope (FESEM) and transmission electron microscope (TEM). Magnetic properties were measured with a Quantum Design MPMS-5S SQUID magnetometer. The diameter of nanoneedles ranges from 50 to 80 nm. The length of the nanoneedles is about micron size. After the sol-gel coating and weak acid etching, silica nanotubes with a shell of 20-40 nm were obtained. Electron energy dispersive X-ray analysis (EDS) indicated that all CaCO₃ nanoneedles were removed during the etching. The nanoparticles were randomly embedded inside the shells of silica nanotubes. Zero-field-cooled (ZFC) and field-cooled (FC) magnetization data in the temperature range of 10 to 300 K were acquired. A field of 100 Oe was applied as the sample was cooled to the lowest temperature and the magnetization was measured as the sample was heated from 5 to 300 K in the field of 100 Oe. The ZFC curve shows a maximum at 291 K, which is the blocking temperature (T_B). MSNTS exhibit superparamagnetism and ferromagnetism above and below the blocking temperature. It is therefore expected that MSNTS can be exploited as delivery vehicles and supports in bioscience applications.