Magnetic Particles, Sensors, and MRI Contrast Agents

TEM images of sodium alginate and poly-L-lysine coated, silica coated iron nanoeyes

Multifunctional Magnetic Nanoparticles

Multifunctional fluorescent and magnetic nanomaterials have broad application utility for bioimaging, magnetic resonance imaging (MRI), magnetic hyperthermia, and drug delivery. An external magnetic field can be used to heat, guide, orient, and image magnetic particles. Particle fluorescence is useful for sensitive target labeling and subsequent imaging. However, fluorescence measurements are difficult to obtain through deep tissue samples due to scattering, attenuation, and autofluorescence background. Both radioluminescent and rare earth doped upconversion materials are suitable alternatives because X-Ray and near-infrared (NIR) deeply penetrate tissue with minimal background. Radioluminescent materials, such as Gd2O2S:Eu, emit highly penetrating red light when excited by blue light, X-Ray, or alpha/beta radiation. Rare earth doped upconversion materials, such as β-NaGdF4:Yb/Er, emit red/NIR light when excited by NIR light. For this reason, our group develops highly stable, iron oxide core radioluminescent and upconversion particles as multimodal MRI and luminescent contrast agents. Targeted drug delivery, with an understanding of release kinetics and in vivo localization, are also explored for further particle functionalization.

Magnetic Sensors

Our group uses magnetically-modulated optical nanoprobes (MagMOONs) in order to study various biophysical processes in vitro and in vivo. Optically tracking magnetically modulated particles through tissue is a challenge for three reasons: first, tissue attenuates both excitation and probe fluorescence light; second, tissue scatters light which causes image blurring; third, tissue autofluorescence obscures fluorescent probe signal. These limitations can be overcome using MagMOONs. MagMOONs are silica particles containing a fluorescent dye and magnetic material. A metal, such as aluminum, is vapor deposited onto one hemisphere of the fluorescent particles in order to generate an orientation dependent fluorescence response. Free MagMOONs in an oscillating magnetic field will blink as they flip between bright and dim orientations, as the metal coated and un-coated hemispheres alternately face the objective during particle rotation. Our group has used MagMOONs to study the enzyme-catalyzed de-gelation of alginate, a material used for both drug delivery and implanted medical devices. Alginate cleavage was indicated by MagMOON blinking after release from the gel. This concept will be applied to detect biofilm growth on biomedical implants, or de-gelation based drug release.

MagMOONs will also be used to track intracellular transport and associated cytotoxicity. With the increasing application of nanoparticles for chemical sensors, chemotherapy and photodynamic therapy delivery agents, as well as viral and non-viral transfection vectors, there is a need to study how nanoparticles are transported through cells and tissues. In addition, micro- and nanoparticle transport plays an important role in toxicity and accumulation of nanoparticles from smoking, environmental inhalation, and particles produced in prosthetic joints.