The wide bandgap and large exciton binding energy of ZnO may generate new applications in bio-imaging after careful surface modifications. Formation of chemically pure ZnO colloidal nanocrystals with controlled size without unwanted by-products or agglomeration has been the major challenge to fully utilize ZnO's unique properties. In this research, colloidal ZnO nanocrystals were synthesized by a soft chemical method. Particle size and colloidal stability were controlled by capping agents. Influences of the surface modifications on particle size, size distribution and photoluminescence properties were investigated. Pure ZnO showed high intensity UV emission and very low intensity in the visible range, indicating good surface morphology of the ZnO nanoparticles with little surface defects. Transmission electron microscopy (TEM) analysis revealed that the capped crystals were close to spherical shape with single-crystal size about 6 nm. X-ray diffraction (XRD) analyses revealed single-phase ZnO nanoparticles. For bio-imaging, emission in visible wavelength range is preferred. Both TiO 2 and SiO 2 were effective in shifting the emission peak to the visible range with high intensity. Optimum capping thickness is 0.5 nm. ZnO-TiO 2 quantum dots (QDs) showed good bio-imaging capability on plant cells. Quantum yields of the pure ZnO and TiO 2 capped ZnO were measured and compared to commercial fluorescence materials.

Polysilsesquioxane (PSQ) nanoparticles are crosslinked homopolymers formed by condensation of functionalized trialkoxysilanes, and provide an interesting platform for developing biologically and biomedically relevant nanomaterials. In this work, the design and synthesis of biodegradable PSQ particles with extremely high payloads of paramagnetic Gd(III) centers is explored, for use as efficient contrast agents for magnetic resonance imaging (MRI). Two new bis(trialkoxysilyl) derivatives of Gd(III) diethylenetriamine pentaacetate (Gd-DTPA) containing disulfide linkages are synthesized and used to form biodegradable Gd-PSQ particles by base-catalyzed condensation reactions in reverse microemulsions. The Gd-PSQ particles, PSQ-1 and PSQ-2, carry 53.8 wt% and 49.3 wt% of Gd-DTPA derivatives, respectively. In addition, the surface carboxy groups on the PSQ-2 particles can be modified with polyethylene glycol (PEG) and the anisamide (AA) ligand to enhance biocompatibility and cell uptake, respectively. The Gd-PSQ particles are readily degradable to release the constituent Gd(III) chelates in the presence of endogenous reducing agents such as cysteine and glutathione. The MR relaxivities of the Gd-PSQ particles are determined using a 3T MR scanner, with r1 values ranging from 5.9 to 17.8 mMs−1 on a per-Gd basis. Finally, the high sensitivity of the Gd-PSQ particles as T1-weighted MR contrast agents is demonstrated with in vitro MR imaging of human lung and pancreatic cancer cells. The enhanced efficiency of the anisamide-functionalized PSQ-2 particles as a contrast agent is corroborated by both confocal laser scanning microscopy imaging and ICP-MS analysis of Gd content in vitro.

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