The upconversion luminescence and magnetism in Yb³⁺/Ho³⁺ co-doped LaF₃ nanocrystals for potential bimodal imaging

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• 作者：Sasidharanpillai S. Syamchand ; Sony George
• 关键词：Upconversion luminescence ; LaF3 nanocrystals ; MRI ; Bimodal imaging ; Holmium ; T2 contrast ; Biomedical applications
• 刊名：Journal of Nanoparticle Research
• 出版年：2016
• 出版时间：December 2016
• 年：2016
• 卷：18
• 期：12
• 全文大小：
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Nanotechnology; Inorganic Chemistry; Characterization and Evaluation of Materials; Physical Chemistry; Optics, Lasers, Photonics, Optical Devices;
• 出版者：Springer Netherlands
• ISSN：1572-896X
• 卷排序：18

文摘

Biocompatible upconversion nanoparticles with multifunctional properties can serve as potential nanoprobes for multimodal imaging. Herein, we report an upconversion nanocrystal based on lanthanum fluoride which is developed to address the imaging modalities, upconversion luminescence imaging and magnetic resonance imaging (MRI). Lanthanide ions (Yb3+ and Ho3+) doped LaF₃ nanocrystals (LaF₃ Yb3+/Ho3+) are fabricated through a rapid microwave-assisted synthesis. The hexagonal phase LaF₃ nanocrystals exhibit nearly spherical morphology with average diameter of 9.8 nm. The inductively coupled plasma mass spectrometry (ICP-MS) analysis estimated the doping concentration of Yb3+ and Ho3+ as 3.99 and 0.41%, respectively. The nanocrystals show upconversion luminescence when irradiated with near-infrared (NIR) photons of wavelength 980 nm. The emission spectrum consists of bands centred at 542, 645 and 658 nm. The stronger green emission at 542 nm and the weak red emissions at 645 and 658 nm are assigned to 5S₂ → ^{5I₈ and 5F₅ → 5I₈ transitions of Ho3+, respectively. The pump power dependence of luminescence intensity confirmed the two-photon upconversion process. The nanocrystals exhibit paramagnetism due to the presence of lanthanide ion dopant Ho3+ and the magnetization is 19.81 emu/g at room temperature. The nanocrystals exhibit a longitudinal relaxivity (r₁) of 0.12 s−1 mM−1 and transverse relaxivity (r₂) of 28.18 s−1 mM−1, which makes the system suitable for developing T2 MRI contrast agents based on holmium. The LaF₃ Yb3+/Ho3+ nanocrystals are surface modified by PEGylation to improve biocompatibility and enhance further functionalisation. The PEGylated nanocrystals are found to be non-toxic up to 50 μg/mL for 48 h of incubation, which is confirmed by the MTT assay as well as morphological studies in HeLa cells. The upconversion luminescence and magnetism together with biocompatibility enables the adaptability of the present system as a nanoprobe for potential bimodal imaging.}