Up-Converting Nanoparticles: Promising Markers for Biomedical Applications

Background

In recent years, biomedical imaging applications have greatly expanded since imaging techniques are key elements of research and diagnosis. Fluorescence imaging is one of the most used applications, with the purpose of prevention, diagnosis, and treatment. Fluorescent compounds named fluorophores or fluorochromes are used both in vitro and in vivo assays, providing increased sensitivity, high spatial and temporal resolution (Rao, Dragulescu-Andrasi, & Yao, 2007), and the possibility of simultaneous use of multiple fluorophores with different properties (multiplexing) (Zijlmans, et al., 1999). Traditional fluorophores currently used for the usual techniques can be fluorescent organic molecules (NADH, Flavin, aromatic amino acids, porphyrins, lipopigments, collagen, and elastin), inorganic compounds with trademark (ethidium bromide, acridine orange, Hoechst, DAPI, FITC, Alexa Fluor, Texas red), quantum dots or fluorescent beads. Their action mechanism is based on single-photon excitation, process that follows Stokes law, according to which the wavelength of the light emitted is always longer than that of the excitation light (Lakowicz, 2006). Phenomenon named down conversion is reprezented schematically în Figure 1.

Figure 1.

Down conversion mechanism