Ciarán Dolan

Synthesis, tailoring and characterization of silica nanoparticles containing a highly stable ruthenium complex

This paper describes the synthesis and characterization of sol-gel silica nanoparticles (NPs) derived from tetraethoxysilane (TEOS) and from tetraethoxysilane and methyltriethoxysilane (TEOS-MTEOS) in which is encapsulated, an in-house synthesized, stable oxygen-sensitive ruthenium complex, ruthenium (II) (bis-2,2-bipyridyl)-2(4-carboxylphenyl) imidazo[4,5-f][1,10]phenanthroline. These NPs were characterized using dynamic light scattering, transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and Brunauer-Emmett-Teller analysis. The spherical, stable and monodispersed NPs have been prepared using the Stöber method. It was found that the addition of prehydrolyzed MTEOS-based sol prepared in an acidic environment to the reaction mixture containing TEOS NPs synthesized for 6 h produced material with increased porosity when compared to pure silica NPs. Oxygen sensitivity, stability, photobleaching and leaching have been characterized. The hybrid NPs exhibit enhanced O₂ sensitivity but a high degree of leaching when compared to pure silica NPs, which have minimum O₂ sensitivity and no leaching.

Polypyridyl substituted BODIPY derivatives; water switchable imaging probes that exhibit halogen substituent dependent localisation in live cells

The synthesis and photophysical properties of water responsive 1,10-phenanthrolyl and 2,2′-bipyridyl substituted BODIPY derivatives prepared as lipid probes for cell imaging are reported. These compounds exhibit intense emission in non-aqueous media that is reversibly extinguished in aqueous media. Halogen substitution at the BODIPY indacene core decreases the emission quantum yields and causes red spectral shifts of emission maxima of the order H > Br > I. The emission was quenched on binding of the phenanthrolyl or bipyridyl to cations Fe2+, Cu2+ and Zn2+. The origin of the water switching effect and the impact of halogen substitution was investigated by modelling the electronic structure of the fluorophore using DFT methods. All compounds showed excellent permeability to live cells and were found, under imaging conditions, to generally exhibit low cytotoxicity. The absence of emission in the aqueous environment facilitated the collection of high contrast images from membranous regions and lipid droplets in live cells. The staining pattern in HeLa cells was found to depend on halogen substitution. Across both bpy and phen derivatives the halogenated probes showed the strongest targeting of lipid droplets within cells whilst the parent unsubstituted compounds were more widely dispersed in the cytoplasm. Resonance Raman imaging was used to map the distribution of probes within the cell and confirmed that the compounds showed strong co-localisation with lipid rich regions of the cell.

Phase partitioning, solvent-switchable BODIPY probes for high contrast cellular imaging and FCS

Lipophilic BODIPY fluorphores, in which the BODIPY core bears pendant dipyrido[3,2-a:2′,3′-c]phenazine (Dppz) or naphthyridyl and cholesterol substituents were designed and prepared as lipid probes for both liposomes and live cell imaging. The probes are non-emissive in water but permeate both GUV and live cell membranes and provide high contrast fluorescence and lifetime imaging of membranous structures and lipid droplets in cells and are suitable for FCS measurements on lipid membranes.