Nanoparticles are biomedical devices capable of a wide range of applications ranging from drug delivery to molecular sensing and bioimaging agents. Within bioimaging, nanoparticles face numerous obstacles in both in vitro and in vivo applications. Upconversion nanoparticles, capable of absorbing photons and emitting photons at a shorter wavelength, provide a promising modality for addressing many of these in vitro and in vivo obstacles, including low background, comprehensive surface coating options, and applications in multimodal imaging. When considering specific applications however, such as monitoring of nanoparticle endocytosis, simpler, more environmentally friendly, and more cost-effective techniques could improve the rate at which research is conducted by reducing the overhead cost and laboratory expertise required to run such an experiment. To those aims, this thesis serves two primary purposes: first to introduce, evaluate, and direct the current research aimed at developing upconversion nanoparticles as a widely used bioimaging modality, and then to develop a simple technique capable of monitoring living cell nanoparticle uptake rates in a model macrophage system.