Ellipsoidal microcavities: electromagnetic properties, fabrication, and use as multispectral MRI agents.

Abstract

Micro- and nanoscale structuring of electromagnetically susceptible materials underpins many recent advances in biomedical imaging, sensing, and treatment.[1,2] From plasmonic nanoparticles[3] and surface plasmon enhanced detectors,[4] to microengineered multispectral magnetic resonance imaging (MRI) agents,[5–7] tailored material geometries enable new functionalities through locally modified fields and amplified signals. This communication introduces a new class of such field-shaping microstructure: the ellipsoidal microcavity. Ellipsoidal particles are already of considerable interest in mathematical packing and granular media studies,[8] and have been shown to self-assemble into anisotropic materials with unique mechanical and optical properties.[9–11] Here we emphasize that there are additional electromagnetic advantages to their use that stem from their unique ability to generate truly uniform local electromagnetic fields. This communication discusses these ellipsoidal field properties and introduces a new microfabrication protocol that produces almost mathematically exact ellipsoids and ellipsoidal cavities. In addition to providing a new route to colloids with well-defined eccentricities that may enable novel self-assembled structure geoemtries, when hollowed out, the remaining ellipsoidal cavities’ uniform fields makes them ideal candidates for a new class of tunable, multispectral MRI agents.