Nanoparticles have attracted considerable recent research interest for a variety of applications and can be used to visualize and characterise biological processes at the molecular and cellular level. They can be exploited as contrast agents for imaging and functionalised to incorporate luminescent moieties to a provide multi-modal imaging capability. This thesis presents a detailed series of studies on a luminescently labelled gold and silica nanoparticles, with the use of optical and electron microscopies to examine their applications. Using surfactant and peptide pre-coatings gold nanoparticles were coated with an organic dye developed bind to the nanoparticle surface. The imaging potential of these novel nanoprobes is explored by examining uptake in vitro in cancer cells. Confocal laser scanning and transmission electron microscopies indicate significant cellular uptake. Nuclear uptake is also observed and possible methods of translocation to the nucleus are discussed. Cell cycle dysregulation is also assessed with no statistically significant perturbations observed. The cellular uptake of 13 nm and 100 nm gold nanoparticles coated with a luminescent ruthenium polypyridyl complex was also investigated. Microscopy studies demonstrated the imaging potential of luminescent nanoprobes upon cellular uptake which was not accompanied significant cytotoxicity. Finally an investigation in to the interaction of luminescent silica particles with dentine is presented. Confocal and scanning electron microscopies enable qualitative comparisons of the dentinal tubule occluding ability of particles coated with surfactants. The data indicate surfactant hydrophobicity is important factor in governing interactions with the dentine and illustrate the potential of luminescence imaging in dentistry.