(232a) Super-Susceptible Magnetic Nanocrystal Clusters for Medicine and Environment Applications

Magnetic nanoparticles have found extensive applications in the field of medicine and water treatment such as drug delivery, cell targeting, hyperthermia, arsenic removal, etc. While the results from the laboratory study of these technologies were quite exciting, the performance of these technologies in real-world applications are often unsatisfactory. One major reason for the unsatisfactory performance of these technologies in real-world applications is the low magnetic field used. Very high magnetic field is usually used in laboratory study of these technologies to achieve good performance. It is extremely expensive to generate high magnetic field over a large area. In addition, high magnetic field may cause damage to human body in some applications. Therefore, real-world applications usually require a relative low magnetic field. The magnetic nanoparticles cannot be sufficiently magnetized at low magnetic field. Thus, the performances of the nanoparticles are not satisfactory, hindering the application of magnetic nanotechnologies in the real world.

Herein we report the super-susceptible magnetic nanostructures for low field applications (lower than 0.05 Tesla). The new nanostructure is a hierarchical structure composed of dozens to thousands of small nanoparticles and it is called magnetic nanocrystal clusters. The magnetic clusters can display susceptibility over 20 times higher than isolated particles, which enables them to be magnetized at low magnetic field. For example, the clusters can reach more than 60% of their saturation magnetization in fluids at magnetic field as low as 0.005 Tesla. The high susceptibility of the clusters arises from the interactions between primary nanoparticles. While the size of clusters can be as large as 300 nanometers, the clusters show no or little remanence or coercivity.

The susceptibility of magnetic clusters depends on both the characteristics and state of clusters. We generated a large library of clusters with different cluster size and primary particle size by controlling the synthesis chemistry. The diameter of clusters can be tuned from 20 to 300 nanometers and the diameter of primary particles can be tuned from 3 to 30 nanometers. It was found both the cluster size and primary particle size have significant influence on the susceptibility of clusters. We also studied the susceptibility of clusters in the state of solid, solid solution and liquid solution. It was found that the state also has significant influence on the susceptibility. The dependence of susceptibility on clusters state is because of the interactions between clusters and the rotation of clusters in liquid. By changing the characteristic and the state of clusters, the susceptibility of clusters can be tuned over a broad range from 5 to 300.

Due to their enhanced susceptibility, the magnetic clusters display excellent performance at low magnetic field in several medicine and environment applications such as hyperthermia, magnetic targeting of cells, magnetic separation, etc. In magnetic hyperthermia, the nanocrystal clusters display specific adsorption rate over 30 times higher than isolate nanoparticles and they can kill tumor cells more efficiently. In magnetic targeting of cells, the clusters deliver cells to target organ more efficiently than isolated nanoparticles. In magnetic separation, the retention rate of nanocrystal clusters is more than 50 times higher than that of isolate nanoparticles at magnetic field of 0.01 Tesla. The enhanced susceptibility of magnetic nanocrystal clusters could pave the way of moving magnetic nanotechnology out of laboratory.