ZnO:Er,Yb,Gd Particles Designed for Magnetic-Fluorescent Imaging and Near-Infrared Light Triggered Photodynamic Therapy

In this paper, fluorescent and magnetic bifunctional ZnO:Er,Yb,Gd particles were synthesized via a simple homogeneous precipitation method. The morphology, size, fluorescent properties, and magnetic properties of the particles can be readily modified by doping with Er³⁺, Yb³⁺, and Gd³⁺. The results revealed that the ZnO:Er,Yb,Gd particles have both down-conversion and up-conversion fluorescence after calcination at high temperatures (>700 °C). The products successfully labled the human hepatocellular carcinoma (HepG2) cells and presented low toxicity even at a high concentration of 2 mg/mL. Being upconverting nanoparticles (UCNPs), the prepared ZnO:Er,Yb,Gd particles exposed to 980 nm near-infrared (NIR) laser light emitted up-conversion fluorescence which could be absorbed by a photodynamic therapy (PDT) drug, methylene blue (MB), and then killed the HepG2 cells via PDT mechanism. In vitro therapeutic investigation evidenced the prominent PDT effects of MB-loaded ZnO:Er,Yb,Gd UCNPs upon NIR light irradiation. In magnetic resonance imaging (MRI) studies, ZnO:Er,Yb,Gd particles revealed a tunable longitudinal relaxivity rate (<i>r</i>₁) from 23.03 mM^–1s^–1 to 36.84 mM^–1 s^–1, which is much larger than the conventional Gd-DTPA and currently reported Gd-base nanoparticles, suggesting it would be a good candidate as an MRI agent. It is expected that these particles have applications in magnetic-fluorescent bimodal imaging and NIR light triggered photodynamic therapy

Designing a Novel Photothermal Material of Hierarchical Microstructured Copper Phosphate for Solar Evaporation Enhancement

Hierarchical microstructured copper phosphate (HCuPO), which could accelerate water evaporation was well designed based on d–d transition of 3d electrons in Cu²⁺ and fabricated via a solvothermal method. A very strong vis–NIR absorption with the maximum at 808 nm was observed for the HCuPO. Upon irradiation of 808 nm NIR laser light, the HCuPO generated heat with a light-to-heat converting efficiency of 41.8%. The reason for this high efficiency was investigated and assigned to a high probability of nonradiative relaxation, which released the energy in form of heat, happened to the excited 3d electrons of Cu²⁺. The proposed photothermal mechanism was quite different from the surface–plasmon mechanism of other Cu-based photothermal materials. By adding HCuPO into polydimethylsiloxane (PDMS), HCuPO–PDMS composite sheets were fabricated. Due to the intrinsic hydrophobicity of PDMS matrix, the sheets were floatable on water surface and the heat generated by HCuPO was confined within water–air interface region. A much sharper temperature gradient and more rapid increase of surface temperature were observed compared with the HCuPO–water dispersion in which the HCuPO particles were dispersed in water. Porous HCuPO–PDMS sheets were fabricated in order to further accelerate water evaporation. Under 808 nm laser irradiation with power density of 1000–2000 W·m^–2, water evaporation rate of salt water (3.5 wt %) was measured to be 1.13–1.85 kg·m^–2·h^–1 for porous floating HCuPO–PDMS, which was 2.2–3.6 times of that measured for ordinary salt water without HCuPO. By using a solar simulator as a light source, a very high solar thermal conversion efficiency of 63.6% was obtained with a power density of 1000 W·m^–2, indicating that solar evaporation of salt water could be greatly enhanced by the well-designed HCuPO

Stable and Biocompatible Colloidal Dispersions of Superparamagnetic Iron Oxide Nanoparticles with Minimum Aggregation for Biomedical Applications

In this article, a simple and scalable method for preparing well-defined and highly stable colloidal dispersions of superparamagnetic iron oxide nanoparticles (IONPs) is reported. The IONPs with narrow size distribution were synthesized by polyol process. Nonhazardous sodium tripolyphosphate (STPP) was immobilized on the surface of IONPs via effective ligand exchange in aqueous phase. Then the STPP-capped IONPs were purified by tangential flow ultrafitration. The polyanionic nature of STPP and its strong coordination capability to iron oxide warrant the IONPs long-term colloidal stability even in phosphate-buffer saline. Because the ligand exchange and purification process did not involve repeated precipitation by organic solvents, the unwanted irreversible aggregation and organic impurities were avoided to the utmost extent. The absence of aggregation renders the IONPs well-defined magnetic behaviors and optimized relaxometric properties for <i>T</i>₁-weighted magnetic resonance imaging. The in vitro cytotoxicity test suggests that the STPP-capped IONPs possess little toxicity. In vivo MRI experiment carried out with a mouse model demonstrates the excellent <i>T</i>₁-weighted MR contrast enhancement capability of the IONPs. This new kind of IONPs is expected to be applicable in various biomedical applications

Porous TiO₂ Nanoparticles Derived from Titanium Metal–Organic Framework and Its Improved Electrorheological Performance

A simple method for synthesis of porous TiO₂ nanoparticles was developed via a two-step route using titanium metal–organic framework (MOF) as a precursor, in which MOFs were first prepared by a cetyltrimethylammonium bromide (CTAB) assisted solvothermal method and then calcined in air at 500 °C. After pyrolysis of precursor MOFs, the anatase TiO₂ inherited the porosity of precursor MOF and possessed a large surface area and uniform pore distribution, which was subsequently adopted as an electrorheological (ER) material by dispersing in silicone oil. ER activities of MOFs and porous TiO₂ based suspensions under the applied electric fields were investigated in a controlled shear rate (CSR) mode. In contrast to MOFs based ER fluids, the suspension of porous TiO₂ exhibited a higher ER efficiency and lower leakage current. Furthermore, the improvement of dielectric properties was found to be responsible for the enhanced ER activity through an investigation of dielectric spectrum