Magnetic nanoparticles

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Monodisperse Fe magnetic nanoparticles with a ferrite shell. Each nanoparticle is roughly 16nm in diameter. (a) Electron micrograph of magnetic nanoparticles; (b) High resolution micrograph; (c) x-ray diffractogram showing the spinel structure of this particular set of nanoparticles; and (d) the magnetization as a function of applied field. Note that these particles exhibit superparamagnetism at room temperature.

Magnetic nanoparticles are a class of nanoparticles, which can be manipulated using magnetic fields. They are typically composed of metals such as iron, cobalt, nickel, and their compounds in sizes ranging from 1 to 100nm [1].

Magnetic nanoparticles commonly exhibit superparamagnetism. Similar to paramagnetic objects, superparamagnetic objects will align themselves with an applied magnetic field; typically, they have larger magnetic susceptibility than paramagnetic materials. When no field is applied, the magnetization of the particle is perturbed by fluctuations in temperature, such that the magnetization of a particle flips randomly and time averages to zero.


Magnetic nanoparticles have many applications, a number of which are in the fields of biotechnology and medicine. Magnetic beads can be attached to cells and other objects and used for manipulations at small length scales. By applying force with a magnet, precise control over the amount of force applied is possible.

Magnetic nanoparticles can also serve as contrast enhancement agents for NMR or MRI techniques. The magnetic nanoparticles, shown in the figure on the right, can be used to decrease the spin-spin relaxation time (T2 relaxation time) of protons in water molecules, allowing the concentration of nanoparticles to be determined. The surfaces of nanoparticles can be functionalized with antibodies to allow them to be targeted to specific pathogens [2].


  1. "Magnetic Nanoparticles." Wikipedia.
  1. Hakho Lee, Tae-Jong Yoon, and Ralph Weissleder. "Ultrasensitive detection of bacteria using core-shell nanoparticles and a NMR-filter system" Angewandte Chemie Internation Edition (2009).