Multispectral MRI contrast through cylindrical nanoshell agents

Introduction Recently it was shown that top-down microfabrication could be used to engineer precisely shaped magnetic microparticles that function as MRI contrast agents with tunable NMR spectral signatures [1]. The agents operated similarly to CEST / PARACEST agents [2,3], except with continuously tunable frequency shifts determined by control of the particle geometry, and with a magnetization-transfer signal acquisition scheme driven by diffusional-, rather than by chemical-exchange processes. The original demonstration was based on a design that, while well suited to conventional lithographic microprocessing [4], depended on complex double-disk magnetic microstructures. Non-conventional microprocessing, however, allows also for the possibility of creating cylindrical magnetic nanoshell structures [5]. Via elementary physical transformations, it can be shown that similar NMR tunability can be achieved through the use of such cylindrical nanoshells, which are in some ways simpler than double-disk structures in that they represent single, rather than complex, magnetic structures. Here NMR results from such cylindrical nanoshell agents are presented, with the work also being taken a step further by releasing these nanoshells from their fabrication substrate and demonstrating automatic magnetic self-alignment and signal acquisition from ensembles of such structures randomly distributed in an agarose gel.