Nanoparticles have made significant contributions to the field of biological and biomedical imaging. Quantum dots have been extensively studied for their unique optical and electronic properties, sharp emission band with broad excitation, and strong resistance to photobleaching. In addition to these properties, their dimensional similarities to biomacromolecules (e. g., DNA and protein) and facile bioconjugation make them excellent agents for biological imaging. Similarly, magnetic nanoparticles (MNPs) have also been studied for biomedical applications, including MRI contrast enhancement, magnetic immobilization, and drug targeting. Recently, hybrid materials that contain both magnetic nano-particles and quantum dots (QDs) have been synthesized. These materials, which have been initially explored as multimodal imaging agents, may also allow for direct mechanical manipulation and simultaneous observation of sub-cellular features.

Here, we present the synthesis and characterization of a new nano-composite, CdTe-FeP magnetic quantum dot nanoparticles. These materials, which exhibit a dumbbell shape morphology are further encapsulated with silica to produce a core-shell structure. The magnetic quantum dots, CdTe-FeP, were prepared through a one-pot chemical method based on high temperature precursor decomposition of both materials in trioctyl phosphine oxide (TOPO). The silica shell was formed using a reverse micro-emulsion technique.

To characterize this material, we investigated the effect of the synthesis conditions and CdTe: FeP mole ratios on magnetic and fluorescent properties as measured by TEM, XRD, UV, XPS, fluorescence spectroscopy, and superconducting quantum interference device (SQUID). Results indicate that nano-composites exhibit magnetic and fluorescent properties; however, the magnetism exhibited by FeP appeared to change from ferromagnetic to paramagnetic after conjugation with CdTe. Also, the quantum yield of CdTe decreased after conjugation. These data suggest an interaction between the magnetic and fluorescent features of the individual particles. These core-shell nanocomposites have potential applications in diagnostics, circulating drug-delivery systems, and treating cancer at its earliest stages.