Luminescent Ink Based on Upconversion of NaYF4:Er,Yb@MA Nanoparticles: Environmental Friendly Synthesis and Structural and Spectroscopic Assessment.

NaYF4:Er,Yb upconversion luminescent nanoparticles (UCNPs) were prepared by hydrothermal methods at 180 °C for 24 h. The X-ray diffraction (XRD) and TEM (transmission electron microscopy) images show that the resulting 60 nm UCNPs possess a hexagonal structure. In this work, maleic anhydride (MA) was grafted on the surface of UCNPs to induce hydrophilic properties. The photoluminescence spectra (PL) show upconversion emissions centered around 545 nm and 660 nm under excitation at 980 nm. The luminescent inks, including UCNPs@MA, polyvinyl alcohol (PVA), deionized water (DI), and ethylene glycol (EG), exhibit suitable properties for screen printing, such as high stability, emission intensity, and tunable dynamic viscosity. The printed patterns with a height of 5 mm and a width of 1.5 mm were clearly observed under the irradiation of a 980 nm laser. Our strategy provides a new route for the controlled synthesis of hydrophilic UCNPs, and shows that the UCNPs@MAs have great potential in applications of anti-counterfeiting packing.

Schiff base rare earth metal complexes: Studies on functional, optical and thermal properties and assessment of antibacterial activity.

We used the condensation chemistry with anthracene­9­carbaldehyde and 3,4­diaminopyridine to form Schiff base (SB) ligand, N2,N3­bis (anthracen­9­ylmethylene) pyridine­3,4­diamine incorporating Er, Pr and Yb rare earth metals to form a series of SB complexes. Surface, structure, thermal, and optical properties of the resulting complexes were investigated using a variety of tools. The characteristic luminescence properties were observed after rare earth metal inclusions in SB. Antibacterial studies were performed against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa in terms of zone of inhibition for SB complexes. The SB-Pr complexes showed better immune behavior against all the pathogens than the other SB metal complexes.

Biocompatibility assessment of up-and down-converting nanoparticles: implications of interferences with in vitro assays.

The safety assessment of nanoparticles (NPs) is crucial during their design and development for biomedicine. One of the prerequisite steps during this evaluation is in vitro testing that employs cell-based assays not always validated and well-adapted for NPs. Interferences with in vitro assays may arise due to the nano-related optical, oxidative, fluorescent, surface and catalytic properties of NPs. Thus, proper validation of each assay system has to be performed for each NP type. This study aimed to evaluate the applicability of the most common in vitro cytotoxicity assays for the safety assessment of up- and down-converting lanthanide-doped NPs. Conventional cell viability tests and fluorescence-based assays for oxidative stress response were selected to determine the biological effects of up- and down-converting NPs to human brain cells. Comparison with known silver and iron oxide NPs was made for verification purposes. Both the plate reader and flow cytometric measurements were examined. The obtained results indicated that both types of Ln-doped NPs interfered to a much lesser extent than metallic NPs. In addition, the great potential of both up- and down-converting NPs for biomedicine was manifested due to their biocompatibility and low toxicity.

Opportunities for Low Cost Processing of Erbium 8-Quinolinolates for Active Integrated Photonic Applications.

Erbium-doped organic emitters are promising active materials for Photonic Integrated Circuits (PICs) due to their emission shown at 1550 nm combined to the potential low cost processing. In particular, Erbium Quinoline (ErQ) gained a strong interest in the last decade for the good emission efficiency. This contribution reports the results derived from the application of ErQ as active core material within a buried optical waveguide, following the development of a purposed optical process to control the refractive index of ErQ and then to define a patterned structure from a single thin film deposition step. The reported results show the potential of Er-doped organic materials for low cost processing and application to planar PICs.

NaYF4:Yb3+/Er3+ nanoparticle-based upconversion luminescence resonance energy transfer sensor for mercury(II) quantification.

Upconversion luminescence is an anti-Stokes' emission process by converting long wavelength near-infrared (NIR, 980 nm) irradiation into shorter wavelength visible light emission, which demonstrates many advantages including no autofluorescence, low damage to samples, no photobleaching, and high sensitivity. Based on the Rhodamine B thiolactone (RBT) functionalized NaYF(4):15%Yb(3+),5%Er(3+) (UCNPs@RBT) nanocomposites, an ultrasensitive, selective, and rapid upconversion luminescence resonance energy transfer (UC-LRET) sensor has been developed for the detection of mercury ions (Hg(2+)) in water. Upconverting luminescence resonance energy transfer from the UCNPs to the RBT derivates occurs after the addition of Hg(2+) ions into the UCNPs@RBT colloidal solution. This UC-LRET recognition of Hg(2+) can be finished within 1 min and other cations have no influence on the detection of mercury ions. This newly developed sensor demonstrates high selectivity toward the mercury ions and enables ultrasensitive and rapid detection of mercury ions in water in the range of 5 nM to 10 µM with a 3σ limit of detection of 3.7 nM. This sensor can be used for a naked-eye detection of Hg(2+) ions via its green upconverting luminescence response under the infrared excitation (980 nm) with the merit of no autofluorescence interference and good photostability. In addition, by dipping the hydrogel of UCNPs@RBT nanocomposites onto the filter paper, a highly selective and convenient luminescent paper sensor for Hg(2+) ions was also developed.

Nondestructive assessment of dentin demineralization using polarization-sensitive optical coherence tomography after exposure to fluoride and laser irradiation.

Previous studies have demonstrated that polarization-sensitive optical coherence tomography (PS-OCT) can be used to image natural and artificial caries in dentin. The purpose of this study was to measure nondestructively the severity of artificial caries lesions in dentin and determine the efficacy of intervention with anticaries agents including fluoride and lasers. Although several studies have assessed the utility of PS-OCT to image caries lesions in enamel and to quantify the lesion severity, only a few studies have focused on lesions in dentin. In this study, images of artificial dentin lesions on extracted human teeth were acquired with PS-OCT. Before exposure to an artificial demineralizing solution, three incisions were made on the sample surfaces using either Er:YAG, Nd:YAG (lambda = 355 nm), or TEA CO(2) lasers and selected areas were treated with topical fluoride to create six unique treatment areas for each of the three laser conditions investigated. The integrated reflectivity and depth of demineralization were calculated for each of the six areas on each sample using the PS-OCT images. Polarized light microscopy (PLM) and transverse microradiography (TMR) were used to measure lesion severity on histological thin sections for comparison. PS-OCT successfully measured the inhibition of demineralization by topical fluoride. Laser irradiation was not particularly effective in increasing or decreasing the rate of dentin demineralization. PLM and TMR corroborated those results. This study demonstrates that PS-OCT can be used to measure demineralization on dentin surfaces and determine the degree of inhibition of demineralization by anticaries agents.