Magnetic nanoparticles in biological vehicles individually characterized for the first time

Magnetic nanostructures are promising tools for medical applications. Embedded in biological structures, they can be directed via external magnetic fields inside the body to release drugs or destroy cancer cells. However, until now, only average information about the magnetic properties of these nanoparticles could be obtained, thus limiting their successful implementations in therapies. Now, a team from HZB has designed and tested a new method to assess the characteristic parameters of each magnetic nanoparticle.

Imagine a tiny vehicle with a nanomagnetic structure, which can be directed through the human body via external magnetic fields. At its destination, the vehicle can release a drug or heat cancer cells without affecting healthy tissue. Scientists from different disciplines are working on this vision to make it come true. A multidisciplinary research group from the Universidad del País Vasco, Leioa, Spain, is exploring the talents of so-called magnetotactic bacteria, which have the surprising property of forming magnetic iron oxide nanoparticles inside their cells. These particles, with a diameter of approximately 50 nanometers (100 times smaller than blood cells), are organized within the bacteria in a chain. The Spanish team is pursuing the idea of ​​using such “magnetic bacteria” as magnetic hyperthermia agents to treat cancer: directed at the cancer site, the magnetic nanostructures must be heated by external fields in order to burn the cells cancerous.

Now they have cooperated with a team of physicists led by Sergio Valencia at HZB to explore their magnetic properties in detail. The degree of success of all of these applications depends substantially on the magnetic properties of the individual nanomagnets. But since the signals from these tiny magnetic structures are quite weak, it is necessary to average the values ​​over thousands of these structures in order to obtain meaningful data.

Average values ​​are not enough

So far, only these average values ​​can be measured, which imposes certain constraints in the design of custom nanomagnet applications. But that has changed. Spanish physicist Lourdes Marcano developed a new method during her postdoctoral stay in the Valencia team at BESSY II: “We can now obtain precise information on the magnetic properties of several individual nanomagnets simultaneously” she says .

Magnetic anisotropy for each particle

The method makes it possible to measure the magnetic properties of individual magnetic nanostructures, even when they are embedded in biological entities. Magnetic imaging with the BESSY II MAXYMUS scanning transmission X-ray microscope, using theoretical simulations, provides information on the so-called magnetic anisotropy of each nanoparticle in the field of view of the microscope. The method has proven itself by determining the magnetic anisotropy of magnetic nanoparticles inside a bacterium. Magnetic anisotropy is an important parameter for controlling and directing magnetic nanoparticles because it describes how a magnetic nanoparticle responds to external magnetic fields applied in an arbitrary direction.

Future standard laboratory technique

“In fact, magnetic imaging of magnetic nanoparticles inside a biological cell with sufficient spatial resolution requires the use of X-ray microscopes. Unfortunately, this is only possible in large research facilities. scale, like BESSY II, providing sufficiently intense X-ray radiation, however, in the future, with the development of compact plasma X-ray sources, this method could become a standard laboratory technique,” ​​says Sergio Valencia.

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Materials provided by Helmholtz-Zentrum Berlin for Materials and Energy. Note: Content may be edited for style and length.

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