Sr2BiF7: A New Bismuth-Based Host Material for Lanthanide Ions Doping: Synthesis, Downshifting, and Upconversion Luminescence Properties for Multimode Anticounterfeiting

A new bismuth-based host material, i.e., Sr2BiF7, is explored in this work. Undoped and lanthanide ion-doped Sr2BiF7 nanomaterials are prepared using a simple coprecipitation technique at 120 °C. The undoped nanomaterials exhibit a blue color under 365 nm excitation. The downshifting and upconversion photoluminescent properties of Er and Yb codoped Sr2BiF7 nanomaterials are investigated. The optimum up-conversion luminescence is produced by nanomaterials doped with 5% Yb3+ and 0.2% Er3+. These nanomaterials show blue and magenta colors upon excitation at 365 and 395 nm wavelengths, respectively. Sr2BiF7 material doped with Er3+ shows green emission, while the codoped Er3+, Yb3+ nanomaterials exhibit an orange-red color under 980 nm light. A specific amount of polyvinyl chloride (PVC) is used for producing luminescent ink with these nanoparticles for multimode anticounterfeiting applications. The letters and patterns written with luminescent ink based on Er3+, Yb3+ doped nanomaterials show blue, magenta, and orange-red colors under 365, 395, and 980 nm light, respectively. These results establish that this material can be effectively used as a multimode photoluminescent covert tag to combat counterfeiting.

Effect of Gd3+, La3+, Lu3+ Co-Doping on the Morphology and Luminescent Properties of NaYF4:Sm3+ Phosphors

The series of luminescent NaYF₄:Sm³⁺ nano- and microcrystalline materials co-doped by La³⁺, Gd³⁺, and Lu³⁺ ions were synthesized by hydrothermal method using rare earth chlorides as the precursors and citric acid as a stabilizing agent. The phase composition of synthesized compounds was studied by PXRD. All synthesized materials except ones with high La³⁺ content (where LaF₃ is formed) have a β-NaYF₄ crystalline phase. SEM images demonstrate that all particles have shape of hexagonal prisms. The type and content of doping REE significantly effect on the particle size. Upon 400 nm excitation, phosphors exhibit distinct emission peaks in visible part of the spectrum attributed to ⁴G_5/2→⁶H_J transitions (J = 5/2-11/2) of Sm³⁺ ion. Increasing the samarium (III) content results in concentration quenching by dipole-dipole interactions, the optimum Sm³⁺concentration is found to be of 2%. Co-doping by non-luminescent La³⁺, Gd³⁺ and Lu³⁺ ions leads to an increase in emission intensity. This effect was explained from the Sm³⁺ local symmetry point of view.

NIR laser scanning microscopy for photophysical characterization of upconversion nanoparticles and nanohybrids

Photophysical characterization of upconversion nanoparticles (UCNPs) and nanohybrids (UCNHs) is more challenging than that of down-conversion nanomaterials. Moreover, it is still difficult to gain knowledge about the homogeneity of the sample and colocalization of emissive chromophores and nanoparticles in nanohybrids. Near infrared laser scanning microscopy (NIR-LSM) is a well-known and useful imaging technique, which enables excitation in the NIR region and has been extensively applied to optical fluorescence imaging of organic fluorophores and nanomaterials, such as quantum dots, which exhibit a short-lived emission. NIR-LSM has recently been used to determine the empirical emission lifetime of UCNPs, thus extending its application range to nanomaterials with a long lifetime emission. Here, we review our previous findings and include new measurements and samples to fully address the potential of this technique. NIR-LSM has proved to be extraordinarily useful not only for photophysical characterization of UCNHs consisting of UCNPs capped with a fluorophore to easily visualize the occurrence of the resonance energy transfer process between the UCNH constituents and their homogeneity, but also to assess the colocalization of the fluorophore and the UCNP in the UCNH; all this information can be acquired on the micro-/nano-meter scale by just taking one image.

A strategy to enhance the up-conversion luminescence of nanospherical, rod-like and tube-like NaYF4: Yb3+, Er3+ (Tm3+) by combining with carbon dots

The luminescence enhanced strategy of combining the material with carbon dots to form CDs@NaYF₄: Yb³⁺, Er³⁺ (Tm³⁺) composites is effective not only for the cubic- and hexagonal-phase materials but also for those with different morphologies.

Construction of Multicolor Upconversion Nanotheranostic Agent for in-situ Cooperative Photodynamic Therapy for Deep-Seated Malignant Tumors

Upconversion nanoparticles (UCNPs)-based photodynamic nanotheranostic agents could address the main drawbacks of photosensitizer molecules (PSs) including instability in aqueous solution and rapid clearance. Due to the relatively weak luminescence intensity of UCNPs and insufficient reactive oxygen species (ROSs), UCNPs-based photodynamic therapy (UCNPs-PDT) was discounted for deep-seated tumors. Thus, we proposed a PSs-modulated sensitizing switch strategy. Indocyanine green (ICG) as an NIR organic dye was proved to effectively enhance the luminescence intensity of UCNPs. Herein, four-color UCNPs were coated with a silica layer which loaded ICG and PSs while the thickness of silica layer was controlled to assist the sensitization function of ICG and activation of PSs. Under the drive of mitochondria-targeting ligand, the prepared nanotheranostic agent would accumulate in the mitochondria where ROSs were in-situ produced and then cell apoptosis was induced. Due to the cooperative PDT and high tissue-penetration depth of NIR laser, the prepared upconversion nanotheranostic agent could achieve significant inhibition on the deep-seated tumors.

Advances in biosensors for the detection of ochratoxin A: Bio-receptors, nanomaterials, and their applications

Ochratoxin A (OTA) is a class of mycotoxin mainly produced by the genera Aspergillus and Penicillium. OTA can cause various forms of kidney, liver and brain diseases in both humans and animals although trace amount of OTA is normally present in food. Therefore, development of fast and sensitive detection technique is essential for accurate diagnosis of OTA. Currently, the most commonly used detection methods are enzyme-linked immune sorbent assays (ELISA) and chromatographic techniques. These techniques are sensitive but time consuming, and require expensive equipment, highly trained operators, as well as extensive preparation steps. These drawbacks limit their wide application in OTA detection. On the contrary, biosensors hold a great potential for OTA detection at for both research and industry because they are less expensive, rapid, sensitive, specific, simple and portable. This paper aims to provide an extensive overview on biosensors for OTA detection by highlighting the main biosensing recognition elements for OTA, the most commonly used nanomaterials for fabricating the sensing interface, and their applications in different read-out types of biosensors. Current challenges and future perspectives are discussed as well.

Advances in nanomaterials for use in photothermal and photodynamic therapeutics (Review)

Nanomaterials play crucial roles in the diagnosis and treatment of diseases. Photothermal and photodynamic therapy, as two minimally invasive therapeutic methods, have promising potential in the diagnosis and prevention of cancer. Recently, many photothermal materials (such as noble metal material, transition metal sulfur oxides, carbon material and upconversion nanomaterial) and photodynamic materials (such as phthalein cyanogen, porphyrins and other dye molecules) have been applied in photothermal therapy (PTT) and photodynamic therapy (PDT). Moreover, as nanomaterials have suitable biocompatibility, these materials have been applied in cancer therapy. In the present review, we summarized the effects of different material types, synthesis methods, material morphologies and surface modifications on the outcomes of cancer therapy. The application of nanomaterials in PTT and PDT was introduced and the advantages and disadvantages of PTT and PDT in the prevention of cancer were discussed. Finally, we discussed the application of nanomaterials in the combination of PTT and PDT in cancer treatment.

Optical and Electrochemical Sensors and Biosensors for the Detection of Quinolones

One major concern associated with food safety is related to residual effects of antibiotics that are widely used to treat animals and result in antimicrobial resistance. Among different groups of antibiotic, the use of quinolones in livestock is of major concern due to the significance of these antimicrobial drugs for the treatment of a range of infectious diseases in humans. Therefore, it is desirable to develop reliable methods for the rapid, sensitive, and on-site detection of quinolone residue levels in animal-derived foods to ensure food safety. Sensors and biosensors are promising future platforms for rapid and on-site monitoring of antibiotic residues. In this review, we focus on recent advancements and modern approaches in quinolone sensors and biosensors.

Heterogeneous growth of palladium nanocrystals on upconversion nanoparticles for multimodal imaging and photothermal therapy

Based on the heterogeneous growth of nano-palladium on UCNPs, a new kind of nanocomposite was developed that can be used for dual-imaging guided photothermal therapy. This smart strategy provides new insights for future development of materials based on the multicomponent nanocomposites.