A method for the growth of uniform silica shells on different size and morphology upconversion nanoparticles

Silica-coated LiYF4:Yb3+, Tm3+ upconverting nanoparticles are non-toxic and activate minor stress responses in mammalian cells

Lanthanide-doped upconverting nanoparticles (UCNPs) are ideal candidates for use in biomedicine. The interaction of nanomaterials with biological systems determines whether they are suitable for use in living cells. In-depth knowledge of the nano-bio interactions is therefore a pre-requisite for the development of biomedical applications. The current study evaluates fundamental aspects of the NP-cell interface for square bipyramidal UCNPs containing a LiYF4:Yb3+, Tm3+ core and two different silica surface coatings. Given their importance for mammalian physiology, fibroblast and renal proximal tubule epithelial cells were selected as cellular model systems. We have assessed the toxicity of the UCNPs and measured their impact on the homeostasis of living non-malignant cells. Rigorous analyses were conducted to identify possible toxic and sub-lethal effects of the UCNPs. To this end, we examined biomarkers that reveal if UCNPs induce cell killing or stress. Quantitative measurements demonstrate that short-term exposure to the UCNPs had no profound effects on cell viability, cell size or morphology. Indicators of oxidative, endoplasmic reticulum, or nucleolar stress, and the production of molecular chaperones varied with the surface modification of the UCNPs and the cell type analyzed. These differences emphasize the importance of evaluating cells of diverse origin that are relevant to the intended use of the nanomaterials. Taken together, we established that short-term, our square bipyramidal UCNPs are not toxic to non-malignant fibroblast and proximal renal epithelial cells. Compared with established inducers of cellular stress, these UCNPs have minor effects on cellular homeostasis. Our results build the foundation to explore square bipyramidal UCNPs for future in vivo applications.

Recent advances in rare earth ion-doped upconversion nanomaterials: From design to their applications in food safety analysis

The misuse of chemicals in agricultural systems and food production leads to an increase in contaminants in food, which ultimately has adverse effects on human health. This situation has prompted a demand for sophisticated detection technologies with rapid and sensitive features, as concerns over food safety and quality have grown around the globe. The rare earth ion-doped upconversion nanoparticle (UCNP)-based sensor has emerged as an innovative and promising approach for detecting and analyzing food contaminants due to its superior photophysical properties, including low autofluorescence background, deep penetration of light, low toxicity, and minimal photodamage to the biological samples. The aim of this review was to discuss an outline of the applications of UCNPs to detect contaminants in food matrices, with particular attention on the determination of heavy metals, pesticides, pathogenic bacteria, mycotoxins, and antibiotics. The review briefly discusses the mechanism of upconversion (UC) luminescence, the synthesis, modification, functionality of UCNPs, as well as the detection principles for the design of UC biosensors. Furthermore, because current UCNP research on food safety detection is still at an early stage, this review identifies several bottlenecks that must be overcome in UCNPs and discusses the future prospects for its application in the field of food analysis.

Europium-Doped Calcium Silicate Nanoparticles as High-Quantum-Yield Red-Emitting Phosphors

Europium ion-activated calcium silicate phosphors (Ca2SiO4:Eu3+) with sharp red-light emission were fabricated via the hydrothermal method. The size of Ca2SiO4:Eu3+ phosphors was controlled between 20 and 200 nm by precursor silicate particle sizes. Systematic studies to determine morphology, crystal phase, and photoluminescence (PL) were carried out for all the phosphors, and their optical efficiencies were compared. We found that the luminescence intensity and emission wavelength of Ca2SiO4:Eu3+ phosphors depend on their particle sizes. Particularly, the Ca2SiO4:Eu3+ synthesized with 20 nm silica seed contains the most intense red emission, high color purity, and high PL quantum yield. For the 20 nm-sized Ca2SiO4:Eu3+ phosphor, PL quantum yields are measured to be above 87.95% and high color purity of 99.8%. The unusually high intensity of 5D0 → 7F4 emission (712 nm) is explained by structural distortion arising from silicate particle size reductions. We show that the obtained phosphor is a suitable candidate for solid-state lighting as a red component through CIE chromaticity coordinate and color purity measurements. Furthermore, the Ca2SiO4:Eu3+ particles are examined for their validity as promising bio-imaging probes through cell labeling and imaging experiments and biodegradability studies.