Single-crystalline MFe2O4 nanotubes/nanorings synthesized by thermal transformation process for biological applications

Abstract

We report a general thermal transformation approach to synthesize single-crystalline magnetic transition metal oxides nanotubes/nanorings including magnetite Fe3O4, maghematite γ-Fe 2O3, and ferrites MFe2O4 (M = Co, Mn, Ni, Cu) using hematite α-Fe2O3 nanotubes/nanorings template. While the straightforward reduction or reduction-oxides process was employed to produce Fe3O4 and γ-Fe2O3, the α-Fe2O3/M(OH)2 core/shell nanostructure was used as precursor to prepare MFe2O 4 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 morpologies. 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 peroxidase 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. © 2009 American Chemical Society.