Magnetic Nanorings and Nanotubes for Cancer Detection and Therapy

Abstract

The idea of using magnetism for healing and therapy can be traced back to the ancient Greeks and Egyptians, who believed that the magical rock, now known as magnetite, was a “cure” for most common ailments. A similar belief was found in the ancient cultures of India and China, where people also used the power of magnets for healing. Nowadays, nanoscale magnetic materials offer novel size-and shape-dependent chemical and physical properties that can be used as an effective and effi cient contrast and therapeutic agent for cancer cell labelling, cell death, separation and detection (Portney and Ozkan 2006; Goya et al. 2008; Sekhon and Kamboj 2010). Thanks to the rapid development of nanomaterials fabrication, people are now able to perform controllable growth of various magnetic nanoparticles including all kinds of ferrites and some metal alloys (Frey et al. 2009). Most of the nanoparticle based cancer work, however, is focused on the biomedical application of ultra-small superparamagnetic nanoparticles (usually spherical iron oxide nanoparticle), in which the small size results in randomized magnetization fl ip at room temperature, thereby leading to a stable magnetic colloid or ferrofl uid (Xie et al. 2009). Though the superparamagnetic nanoparticles have been shown to have many advantages in biomedical applications and some of them are also commercially available, many drawbacks remain that need improvement. For instance, as a contrast agent for magnetic resonance imaging (MRI) applications, superparamagnetic iron oxide nanoparticles (SPIO) with lowsaturation magnetization as well as low chemical and physical stability induced by its small size lead to poor enhancement in the spin-echo MR effect (Jun et al. 2005). In this chapter, we will focus on novel hollow structure magnetic nanoparticles such as nanorings and nanotubes. Tailoring the size and shape of these nanoparticles together with their unique porous structures enhances tuneability and magnetic properties, thereby leading to high performance practical applications in biomedicine as compared to solid SPIO (Cheng and Sun 2010). The potential use of magnetic nanorings/nanotubes in cancer diagnostics and therapy will be discussed. Because magnetite (Fe3O4)has high biocompatibility, it is the most prevailing candidate in biomedicine and therefore, we will focus primarily on the biomedical applications of iron oxide nanorings/ nanotubes in this chapter; other magnetic hollow materials will not be discussed as they may exhibit similar properties. We will also discuss the various approaches to fabricate such hollow structures and their unique magnetic properties. A few examples on the use of these magnetic nanorings and nanotubes in cancer detection and therapy will be provided. We would like to emphasize that the area of magnetic nanorings and nanotubes on nanomedicine has not been well developed and many novel phenomena that occur in such a system require further investigation. The aim of this chapter is to provide an overview on this rapidly developing area and to explore its potential in cancer detection and therapy.