Magnetite (Fe₃O₄) nanoparticles with uniform sizes of 10, 20, and 31 nm were prepared by thermal decomposition of Fe(III) oleate or mandelate in a high-boiling point solvent (>320 °C). To render the particles with hydrophilic and antifouling properties, their surface was coated with a PEG-containing bisphosphonate anchoring group. The PEGylated particles were characterized by a range of physicochemical methods, including dynamic light scattering, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and magnetization measurements. As the particle size increased from 10 to 31 nm, the amount of PEG coating decreased from 28.5 to 9 wt.%. The PEG formed a dense brush-like shell on the particle surface, which prevented particles from aggregating in water and PBS (pH 7.4) and maximized the circulation time in vivo. Magnetic resonance relaxometry confirmed that the PEG-modified Fe₃O₄ nanoparticles had high relaxivity, which increased with increasing particle size. In the in vivo experiments in a mouse model, the particles provided visible contrast enhancement in the magnetic resonance images. Almost 70% of administrated 20-nm magnetic nanoparticles still circulated in the blood stream after four hours; however, their retention in the tumor was rather low, which was likely due to the antifouling properties of PEG.

In this report, monodisperse upconversion NaYF₄:Yb³⁺/Er³⁺ 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 NaYF₄:Yb³⁺/Er³⁺@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 ¹²⁵I 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 upconversion ¹²⁵I-radiolabeled NaYF₄:Yb³⁺/Er³⁺@PEG nanoparticles are prospective for near-infrared (NIR) photothermal/photodynamic and SPECT/CT cancer theranostics.

We show that the cloud point temperature (T_CP) of thermoresponsive polyacrylamides is considerably lower in physiologically relevant solvents (phosphate-buffered saline, serum) than in pure water. This decrease of T_CP may be critical for some biomedical applications.

In this study, water-dispersed thermo-responsive boron nitride nanotubes (BNNTs) were prepared in a simple two-step process, where on the first step oligoperoxide was grafted via the interaction of amino groups (defects) of BNNTs with pyromellitic chloroanhydride fragments in oligoperoxide molecules. The second step involves N-isopropylacrylamide (NIPAM) graft polymerization ‘from the surface’ of oligoperoxide-functionalized BNNTs resulting in poly(N-isopropylacrylamide) (PNIPAM) coating. The pristine and functionalized BNNTs were characterized by thermogravimetric analysis, Fourier transform infrared spectroscopy, ultraviolet–visible spectrophotometry, dynamic light scattering, scanning electron microscopy and atomic force microscopy. PNIPAM-functionalized BNNTs exhibit excellent dispersibility in water and possess thermo-responsive properties. The water-dispersion of thermo-responsive PNIPAM-functionalized BNNTs can help their potential use in biomedical applications as ‘smart’ surfaces, nanotransducers and nanocarriers.