Читать книгу Magnetic Nanoparticles in Human Health and Medicine - Группа авторов - Страница 38

The use of magnetic nanoparticles has been the subject of great interest for their use in various applications such as the high‐density storage of data (Weller and Doerner 2000), magnetic energy (Zeng et al. 2002), magnetic separations (Hahn et al. 2007), drug delivery (Pulfer et al. 1999), and hyperthermia treatments (Jordan et al. 1999).

The peculiar properties of these nanoparticles have allowed developing remarkable multifunctional systems in nanomedicine. In particular, the possibility to temporarily magnetize the nanomaterial, when an external magnetic field is applied, allows obtaining a device that can be remotely activated and on‐demand. Obviously, even the individual nanoparticles have some limitations, such as the low concentration that is usually achieved at the target site when administrated into the bloodstream. Furthermore, these nanoparticles are perfectly stable from the colloidal point of view, but since the magnetization associated with the single nanoparticle is very low, they behave like a ferrofluid; therefore, it is difficult, or better impossible, to separate them from a suspension or to guide them inside a vessel by the magnetic field. To overcome these and other inherent limitations, one possibility is represented by the clustering of magnetic nanoparticles in colloidal assemblies. When the nanoparticles are inserted into a super‐structure, specific forces are activated or enhanced, which allow arising different properties compared to the single nanoparticles (but limiting, in certain cases, the advantages of the individual ones).

The assembly (Whitesides and Grzybowski 2002; Fialkowski et al. 2006) is undoubtedly a highly exciting process due to the evolution of the individual nanostructure into higher‐ordered nanostructures. The assembling application is realized in several fields, as systems serving as ultrasensitive biosensors (Service 2003), highly conductive nanowires of uniform‐width (Yan et al. 2003), ordered two dimensional (2D) nanoparticle arrays exhibiting unique electronic properties (Dorogi et al. 1995; Murray et al. 2000; Hecht 2005; Shevchenko et al. 2006), and materials of overall macroscopic dimensions and showing unusual bulk properties.

In this chapter, different aspects of nanoparticle clustering, with particular emphasis on magnetic ones and on the possible use in the field of nanomedicine, are discussed. Within this scenario, all the forces that govern at the nanoscale the generation of organized clusters of nanoparticles, and the balance between the different components able to control the formation of regular and functional structures, are initially analyzed. Then, in a more applicative section, some examples of magnetic nanoclusters that have biomedical relevance are highlighted; the shown nanocomposites are classified according to the type of preparation and/or the type of molecule (e.g. polymers, polysaccharides) which has been used to control and stabilize the obtained cluster. Finally, some studies that resulted in the use of magnetic clusters to the animal study, applying a theranostic approach, are commented in more detail. The purpose of this chapter is mainly to provide to the reader the bases for evaluating the advantages deriving from nanoparticle clustering and to report the most recent studies with relevance in the biomedical field, thus trying to illustrate the advantages of single techniques used.