About Mingliang’s research on Application of Functionalization of Syntheticantiferromagnetic Nanoparticles:

Magnetic nanoparticles are widely used in biology and medicine. In order to produce large signal per single particle or to manipulate these particles under significantly low magnetic field gradients, as in the case of bio-sensing and magnetic sorting, those particles with high moments are often desired. Though commonly used, chemically synthesized superparamagnetic nanoparticles suffer from difficulty in reaching higher moments by simply increasing the size, which will cause the coercivity due to the superparamagnetic limit. Synthetic antiferromagnetic (SAF) particles, on the other hand, do not have the size restriction, and thus they can have much higher magnetic moments, making them promising in biological application. However, before they can be used, two problems must be solved. First, the fabrication process must be modified to increase the efficiency of making these particles and must be amenable to scaling up when large quantities of particles are desired. Second, ways must be found to functionalize these SAF particles through linkage with biomolecules, which is essential for biological application.

The fabrication process can be improved via both reducing the processing time and increasing the throughput. In conventional nanoimprint technique, one layer of Cu is deposited onto the substrate as the release layer, introducing several time-consuming deposition and ion milling processes. In this work, durimide is chosen as the alternative release layer, which can be easily spin-coated onto the substrate in a few minutes. Moreover, owing to the new deposition tool, 24 wafers, rather than one at a time, can be deposited simultaneously, which significantly increases the fabrication efficiency.

In terms of the second problem, surface modification of the particles is required to provide a friendly interface for specific biomolecule attachment. Among those candidates, silanes are the most popular ones, covalently connecting the surface with functional group. In particular, 3-Aminopropyl trimethoxysilane (APTMS) is chosen to graft amino group onto the particles. After that, these particles can be biotinylated, followed by conjugation with streptavidin, enabling further biological experiment.

Finally, these functionalized particles will be used in biological and medical application. Numerous experimental results, including that from biomolecule purifications and cell separations, magnetic resonance imaging (MRI) contrast agents, and biomagnetic sensing, have been reported using commercialized iron oxide nanoparticles. These experiments will be repeated using our new particles and hopefully much better results will be attained over the course of the Ph.D. thesis research.