Abstract
Upconverting nanoparticles (UCNPs) are promising, new imaging probes capable of serving as multimodal contrast agents. In this study, monodisperse and ultrasmall core and core–shell UCNPs were synthesized via a thermal decomposition method. Furthermore, it was shown that the epitaxial growth of a NaGdF4 optical inert layer covering the NaGdF4:Yb,Er core effectively minimizes surface quenching due to the spatial isolation of the core from the surroundings. The mean diameter of the synthesized core and core–shell nanoparticles was ≈8 and ≈16 nm, respectively. Hydrophobic UCNPs were converted into hydrophilic ones using a nonionic surfactant Tween 80. The successful coating of the UCNPs by Tween 80 has been confirmed by Fourier transform infrared (FTIR) spectroscopy. Scanning electron microscopy (SEM), powder X-ray diffraction (XRD), photoluminescence (PL) spectra and magnetic resonance (MR) T1 relaxation measurements were used to characterize the size, crystal structure, optical and magnetic properties of the core and core–shell nanoparticles. Moreover, Tween 80-coated core–shell nanoparticles presented enhanced optical and MR signal intensity, good colloidal stability, low cytotoxicity and nonspecific internalization into two different breast cancer cell lines, which indicates that these nanoparticles could be applied as an efficient, dual-modal contrast probe for in vivo bioimaging.
Highlights
Lanthanide-doped multimodal upconverting nanoparticles (UCNPs), which can convert near-infrared (NIR) radiation into visible light, have been extensively investigated due to the advantages associated with their unique optical properties [1]
We focus on studies of multimodal core–shell NaGdF4:Yb,Er coated with NaGdF4 (NaGdF4:Yb,Er@NaGdF4) UCNPs synthesis and demonstrate the effective surface modification method that uses a surfactant polysorbate 80 (Tween 80, polyoxyethylene sorbitan laurate)
That signifies that the Gd3+ ions in the shell of the UCNPs are the major contributors toward the relaxation of water protons, and the UCNP core does not show any significant effect towards relaxivity enhancement. It has been shown in the literature that reduced water access to the Gd3+ ions may yield reduced values for magnetic resonance (MR) signal enhancement [29,30]. These observations indicate that both core and core–shell UCNPs could be applied as efficient magnetic resonance imaging (MRI) contrast agents as they both present enhanced MR signal intensity
Summary
Lanthanide-doped multimodal upconverting nanoparticles (UCNPs), which can convert near-infrared (NIR) radiation into visible light, have been extensively investigated due to the advantages associated with their unique optical properties [1]. The study of Cascales et al showed that ultrasmall Yb:Er:NaGd(WO4)2 UCNPs could be successfully covered with Tween 80 and are internalized by human mesenchymal stem cells without triggering their metabolic activity, but still no information has been presented about uptake of these nanoparticles into different types of cancer cells [22].
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