Single-Crystalline MFe2O4 Nanotubes/Nanorings Synthesized by Thermal Transformation Process for Biological Applications

We report a general thermal transformation approach to synthesize single-crystal line magnetic transition metal oxides nanotubes/nanorings including magnetite Fe3O4, maghematite gamma-Fe2O3, and ferrites MFe2O4 (M = Co, Mn, Ni, Cu) using hematite alpha-Fe2O3 nanotubes/nanorings template. While the straightforward reduction or reduction-oxides process was employed to produce Fe3O4 and gamma-Fe2O3, the alpha-Fe2O3/M(OH)(2) core/shell nanostructure was used as precursor to prepare MFe2O4 nanotubes via MFe2O4-x, (0 < X < 1) intermediate. The transformed ferrites nanocrystals retain the hollow structure and single-crystalline nature of the original templates. However, the crystallographic orientation-relationships of cubic spinel ferrites and trigonal hematite show strong correlation with their morpologles. The hollow-structured MFe2O4 nanocrystals with tunable size, shape, and composition have exhibited unique magnetic properties. Moreover, they have been demonstrated as a highly effective peroxiclase mimic catalysts for laboratory immunoassays or as a universal nanocapsules hybridized with luminescent QDs for magnetic separation and optical probe of lung cancer cells, suggesting that these biocompatible magnetic nanotubes/nanorings have great potential in biomedicine and biomagnetic applications.