Up-Converting Nanoparticles: Promising Markers for Biomedical Applications

Up-Converting Nanoparticles: Promising Markers for Biomedical Applications

Livia Petrescu (University of Bucharest, Romania), Speranta Avram (University of Bucharest, Romania), Maria Mernea (University of Bucharest, Romania) and Dan Florin Mihailescu (University of Bucharest, Romania)
DOI: 10.4018/978-1-5225-3158-6.ch011
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Abstract

Up-converting nanoparticles are dielectric crystalline particles doped with rare-earth ions such as Yb3+, Er3+, Tm3+, Ho3+, Nd3+, etc. When excited in infrared, they emit visible radiation. Used as markers, they present significant advantages in comparison to traditional fluorophores: sharp emission lines, superior photostability, resistence to photobleaching, no blinking and lack of toxicity. Infrared radiation is less harmful to cells avoiding tissue degradation, minimizes auto-fluorescence from endogenous biocomponents offering a good signal-to-background ratio and penetrates tissues deeply. In spite of the great advantages of using up-converting nanoparticles for biomedical applications, there are still some limitations. These refer to identification of optimal size suited for specific samples, prevention of aggregation, water stability/dispersibility, optical efficiency and biocompatibility. This chapter reviews principal characteristics of up-converting nanoparticles and issues related to their use in biomedical applications.
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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

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