Advances in Functional Micro-Nanoimaging Probes by Zhe Liu

Author:Zhe Liu
Language: eng
Format: epub
ISBN: 9789811048043
Publisher: Springer Singapore

Up-Conversion Nanoparticles (UC NPs)

As has been mentioned, most conventional fluorescence techniques for bio-imaging are based in single-photon excitation, which is excited by high-energy light and hence emits low-energy fluorescence. In contrast, up-conversion nanoparticles have attracted significant attention as a result of their unique ability to generate high-energy emissions (shorter wavelength) under low-energy excitations (longer wavelength) [98]. UC NPs exhibit many advantages, such as narrow-bandwidth emission, a long lifetime, tunable emission, high photostability, and high resistance to photo-bleaching. Moreover, less background autofluorescence and light scattering make imaging with deep tissue light penetration possible. All these features make them attractive optical probes in vitro and in vivo [99–102]. To date, the most popular UC NPs are based on lanthanide elements with Er3+, Tm3+, and Ho3+ being the most commonly used emitters [98, 103].

Recent studies on UC NPs focus on their applications in functional bio-imaging. They can be used for lymph imaging, [104, 105] tumor-targeted imaging [106–108] and cell tracking [109–111] Li developed RGD-labeled up-conversion nanophosphors (UC NPs) as luminescent labels for tumor-targeting imaging (Fig. 3.11). The high affinity of the arginine-glycine-aspartic peptide c(RGDFK) to the αvβ3 integrin receptor on human glioblastoma tumor cells U87MG confers UC NPs with great tumor-targeting ability. UC NPs were dispersed with an average diameter of ~25.8 nm with a round shape. Furthermore, they investigated the time course series of in vivo imaging of the tumor-bearing mice injected with UC NP-RGD from 1 to 24 h. Even at 24 h, there was high fluorescence signal in U87MG tumor site while no signal was detected in MCF-7 tumor site due to the UC NPs’ highly specific binding activity toward tumors, which is suitable for tumor targeting and visualization in living mice with high-contrast images [107, 112].

Fig. 3.11High-contrast up-conversion luminescence peptide-labeled nanophosphors (UC NPs) used for tumor-targeting imaging. a Ill Scheme of the synthesis of UCNP-Arginine-Glycine-Asparatic (RGD); b TEM images of UC NP-RGD samples; c Time-dependent in vivo up-conversion luminescence imaging of subcutaneous U87MG (left hind leg, indicated by short arrows) and MCF-7 (Michigan Cancer Foundation-7) tumor (right hind leg, indicated by long arrows) borne by athymic nude mice after intravenous injection of UC NP-RGD over a 24 h.

Note Reprinted with permission from Xiong et al. [107]. Copyright 2009 American Chemical Society

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