Oxidation and surface modifications boost heat capacity of magnetic iron oxide nanoparticles

Due to their ability to generate heat under alternating magnetic fields, magnetic iron oxide nanoparticles (MIONs) have shown promise for applications ranging from water treatment to cancer thermoablation. In many of these uses, it is crucial to generate a high level of heat with a low dose of MIONs. One new approach looks to substantially increase the amount of heat MIONs can apply.

Jiang et al. demonstrated the effects of controlled oxidation and surface modifications on increasing the specific absorption rate of MIONs. The group synthesized and systematically characterized the physical properties of MIONs, showing that oxidation caused MIONs to transition from magnetite to maghemite, which allowed the heat capacity to double through nanocrystal oxidation or surface modification.

The paper provides a method of how to better engineer MIONs for magnetic heating as well as provides a better understanding of the physiochemical phenomena related to magnetic nanoparticle heating.

“Researchers in the field rely on two approaches to increase heating capacity of MIONs: increasing their size and doping iron oxide nanocrystals with other metal elements,” said author Gang Bao. “Our paper showed that there are new ways to increase the heating capacity of MIONs, which opens new avenues to optimize the design of magnetic nanoparticles.”

The group tested MIONs with different core sizes and coatings, including phospholipids bound to polyethylene glycol and triethylenetetramine. The MION nanocrystals measured less than 20 nanometers, a crucial size to ensure they remain supereparamagnetic and don’t aggregate in aqueous solutions.

Bao next looks to further explore why changing the MION coating has such an impact on heating capacity and to identify optimal coatings.

Source: “Controlled oxidation and surface modification increase heating capacity of magnetic iron oxide nanoparticles,” by Kaiyi Jiang, Qingbo Zhang, Daniel Torres Hinojosa, Linlin Zhang, Zhen Xiao, Yu Yin, Sheng Tong, Vicki L. Colvin, and Gang Bao, Applied Physics Reviews (2021). The article can be accessed at https://doi.org/10.1063/5.0042478 .