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In this report, monodisperse upconversion NaYF:Yb/Er nanoparticles with superior optical properties were synthesized by the oleic acid-stabilized high-temperature co-precipitation of lanthanide chlorides in octadec-1-ene as a high-boiling organic solvent. To render the particles with biocompatibility and colloidal stability in bioanalytically relevant phosphate buffered saline (PBS), they were modified by using in-house synthesized poly(ethylene glycol)-neridronate (PEG-Ner), a bisphosponate. The NaYF:Yb/Er@PEG nanoparticles showed excellent long-term stability in PBS and/or albumin without any aggregation or morphology transformation. The in vitro cytotoxicity of the nanoparticles was evaluated using primary fibroblasts (HF) and a cell line derived from human cervical carcinoma (HeLa). The particles were subsequently modified by using Bolton-Hunter-hydroxybisphosphonate to enable radiolabeling with I for single-photon emission computed tomography/computed tomography (SPECT/CT) bimodal imaging to monitor the biodistribution of the nanoparticles in non-tumor mice. The bimodal upconversionI-radiolabeled NaYF:Yb/Er@PEG nanoparticles are prospective for near-infrared (NIR) photothermal/photodynamic and SPECT/CT cancer theranostics.

Materials with nano-sized architecture currenly attract a lot of attention for various applications because they possess many unique properties. Several of the currently most studied applications of nanotechnology are in medicine, especially in the delivery of chemical drugs, and also in nuclear medicine, which is the focus of this review. The main areas of interest for nano-sized systems exploitable in nuclear medicine are imaging of reticuloendothelial system by single photon emission tomography, radiosynovectomy with beta-emitter-labeled particles, and diagnostic or therapeutic cancer applications exploiting passive targeting of radionuclides to solid tumors by enhanced permeation and retention (EPR) effect, or by active targeting approaches.

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