Porous upconversion nanostructures as bimodal biomedical imaging contrast agents

Abstract

Lanthanide ions doped upconversion nanoparticles (UCNPs) hold great promise as the imaging contrast agent for multimodal medical imaging techniques for diagnosis, including fluorescent bioimaging, magnetic resonance imaging, and computed tomography. However, the maximized signal values of fluorescence and MRI cannot be achieved simultaneously from the same upconversion nanoparticles structures because high specific surface areas can benefit the signal gaining of MRI while big size can induce brighter fluorescent imaging. In this work, we designed and fabricated novel core-porous shell structures for UCNPs with much-enhanced signal values for both fluorescent imaging and MRI. The core-porous shell UCNPs were synthesized via a post-treatment process after an inert shell was coated onto the core UCNPs. The formation mechanism was carefully investigated. The fluorescent and magnetic resonance properties have been detailed characterized and compared from core, core-shell and core-porous UCNPs. Large and bright UCNPs in fluorescence and MRI have been achieved and great potential as the dual-modal contrast agent.