Xuejiao Li

UV-Emitting Upconversion-Based TiO2 Photosensitizing Nanoplatform: Near-Infrared Light Mediated in Vivo Photodynamic Therapy via Mitochondria-Involved Apoptosis Pathway

Photodynamic therapy (PDT) is a promising antitumor treatment that is based on the photosensitizers that inhibit cancer cells by yielding reactive oxygen species (ROS) after irradiation of light with specific wavelengths. As a potential photosensitizer, titanium dioxide (TiO2) exhibits minimal dark cytotoxicity and excellent ultraviolet (UV) light triggered cytotoxicity, but is challenged by the limited tissue penetration of UV light. Herein, a novel near-infrared (NIR) light activated photosensitizer for PDT based on TiO2-coated upconversion nanoparticle (UCNP) core/shell nanocomposites (UCNPs@TiO2 NCs) is designed. NaYF4:Yb(3+),Tm(3+)@NaGdF4:Yb(3+) core/shell UCNPs can efficiently convert NIR light to UV emission that matches well with the absorption of TiO2 shells. The UCNPs@TiO2 NCs endocytosed by cancer cells are able to generate intracellular ROS under NIR irradiation, decreasing the mitochondrial membrane potential to release cytochrome c into the cytosol and then activating caspase 3 to induce cancer cell apoptosis. NIR light triggered PDT of tumor-bearing mice with UCNPs@TiO2 as photosensitizers can suppress tumor growth efficiently due to the better tissue penetration than UV irradiation. On the basis of the evidence of in vitro and in vivo results, UCNPs@TiO2 NCs could serve as an effective photosensitizer for NIR light mediated PDT in antitumor therapy.

Host-Sensitized Luminescence Properties in CaNb2O6:Ln3+ (Ln3+ = Eu3+/Tb3+/Dy3+/Sm3+) Phosphors with Abundant Colors

A series of Ln(3+) (Ln(3+) = Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+)) ion doped CaNb2O6 (CNO) phosphors have been prepared via the conventional high-temperature solid-state reaction route. The X-ray diffraction (XRD) and structure refinement, diffuse reflection, photoluminescence (PL), and fluorescent decay curves were used to characterize the as-prepared samples. Under UV radiation, the CNO host present a broad emission band from about 355 to 605 nm centered around 460 nm originating from the NbO6 octahedral groups, which has spectral overlaps with the excitation of f-f transitions of Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+) in CNO:Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+) samples. They show both host emission and respective emission lines derived from the characteristic f-f transitions of activators, which present different emission colors owing to the energy transfer from the NbO6 group in the host to Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+) with increasing activator concentrations. The decreases of decay lifetimes of host emissions in CNO:Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+) demonstrate the energy transfer from the hosts to Eu(3+)/Tb(3+)/Dy(3+)/Sm(3+). The energy transfer mechanisms in CNO:Eu(3+)/Tb(3+)/Dy(3+) phosphors have been determined to be a resonant type via dipole-dipole mechanisms. For CNO:Sm(3+), the metal-metal charge transfer transition (MMCT) might contribute to the different variations of decay lifetimes and emission intensity from CNO:Eu(3+)/Tb(3+)/Dy(3+) samples. The best quantum efficiency is 71.2% for CNO:0.01/0.02Dy(3+). The PL properties of as-prepared materials indicate the promising application in UV-pumped white-emitting lighting diodes field.

Electrospun Upconversion Composite Fibers as Dual Drugs Delivery System with Individual Release Properties

Novel multifunctional poly(ε-caprolactone)-gelatin encapsulating upconversion core/shell silica nanoparticles (NPs) composite fibers as dual drugs delivery system (DDDS), with indomethacin (IMC) and doxorubicin (DOX) releasing in individual release properties, have been designed and fabricated via electrospinning process. Uniform and monodisperse upconversion (UC) luminescent NaYF4:Yb(3+), Er(3+) nanocrystals (UCNCs) were encapsulated with mesoporous silica shells, resulting in the formation of core/shell structured NaYF4:Yb(3+), Er(3+)@mSiO2 (UCNCs@mSiO2) NPs, which can be performed as DOX delivery carriers. These UCNCs@mSiO2 NPs loading DOX then were dispersed into the mixture of poly(ε-caprolactone) (PCL) and gelatin-based electrospinning solution containing IMC, followed by the preparation of dual drug-loaded composite fibers (DDDS) via electrospinning method. The drugs release profiles of the DDDS were measured, and the results indicated that the IMC and DOX released from the electrospun composite fibers showed distinct properties. The IMC in the composite fibers presented a fast release manner, while DOX showed a sustained release behavior. Moreover, the UC luminescent intensity ratios of (2)H(11/2)/(4)S(3/2)-(4)I(15/2) to (4)F(9/2)-(4)I(15/2) from Er(3+) vary with the amounts of DOX in the system, and thus drug release can be tracked and monitored by the luminescence resonance energy transfer (LRET) mechanism.

Crystal-Site Engineering Control for the Reduction of Eu3+ to Eu2+ in CaYAlO4: Structure Refinement and Tunable Emission Properties

In this article, Eu-activated CaYAlO4 aluminate phosphors were synthesized by a solid-state reaction. Under UV light excitation, characteristic red line emission of Eu(3+) was detected in the range of 570-650 nm. In addition, we introduced crystal-site engineering approach into the CaYAlO4 host through incorporation of Si(4+)-Ca(2+) to replace Al(3+)-Y(3+), which would shrink the AlO6 octahedrons, accompanied by the expansion of CaO9 polyhedron, and then enable the partial reduction of Eu(3+) to Eu(2+). The crystal structure and underlying mechanism have been clarified on the basis of the Rietveld refinement analysis. The PL spectra of Ca0.99+xY1-xAl1-xSixO4:Eu0.01 (x = 0-0.30) exhibit both green emission of Eu(2+) (4f(6)5d(1)-4f(7), broadband around 503 nm) and red-orange emission of Eu(3+) ((5)D0-(7)F1,2, 593 and 624 nm) under UV light excitation with a quantum yield of 38.5%. The CIE coordinates of Ca0.99+xY1-xAl1-xSixO4:Eu0.01 (x = 0-0.30) phosphors are regularly shifted from (0.482, 0.341) to (0.223, 0.457) with increasing x, which would expand the application of Eu. Furthermore, this investigation reveals the correlations of structure and property of luminescent materials, which would shed light on the development of novel phosphors suitable for lighting and display applications.

Soft-chemical synthesis and tunable luminescence of Tb3+, Tm3+/Dy3+-doped SrY2O4 phosphors for field emission displays

Tb(3+), Tm(3+), and Dy(3+)-activated SrY2O4 phosphors have been prepared via Pechini-type sol-gel method. X-Ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL) and lifetimes, as well as cathodoluminescence (CL) spectra were used to characterize the samples. Under low-voltage electron beam excitation, the Tb(3+)-doped samples show a green luminescence, with a better CIE coordinates and higher emission intensity than the commercial product ZnO: Zn. Blue and yellow emissions could be obtained by doping with Tm(3+) and Dy(3+), respectively. A color-tunable emission in SrY2O4 phosphors can be realized by co-doping with Tm(3+) and Dy(3+). White cathodoluminescence (CL) has been realized in a single-phase SrY2O4 host by co-doping with Tm(3+) and Dy(3+) for the first time with CIE (0.315, 0.333). Furthermore, the cathodoluminescence (CL) properties of SrY2O4: Tb(3+)/Tm(3+)/Dy(3+) phosphors including the dependence of CL intensity on accelerating voltage and filament current, the decay behaviour of CL intensity under electron bombardment, and the stability of CIE chromaticity coordinate have been investigated in detail. The as-prepared phosphors might be promising for use in field-emission display (FED) devices.

Aptamer-Mediated Up-conversion Core/MOF Shell Nanocomposites for Targeted Drug Delivery and Cell Imaging

Multifunctional nanocarriers for targeted bioimaging and drug delivery have attracted much attention in early diagnosis and therapy of cancer. In this work, we develop a novel aptamer-guided nanocarrier based on the mesoporous metal-organic framework (MOF) shell and up-conversion luminescent NaYF4:Yb3+/Er3+ nanoparticles (UCNPs) core for the first time to achieve these goals. These UCNPs, chosen as optical labels in biological assays and medical imaging, could emit strong green emission under 980 nm laser. The MOF structure based on iron (III) carboxylate materials [MIL-100 (Fe)] possesses high porosity and non-toxicity, which is of great value as nanocarriers for drug storage/delivery. As a unique nanoplatform, the hybrid inorganic-organic drug delivery vehicles show great promising for simultaneous targeted labeling and therapy of cancer cells.

Rapid, Large-Scale, Morphology-Controllable Synthesis of YOF:Ln3+ (Ln = Tb, Eu, Tm, Dy, Ho, Sm) Nano-/Microstructures with Multicolor-Tunable Emission Properties

YOF:Ln(3+) (Ln = Tb, Eu, Tm, Dy, Ho, Sm) nano-/microstructures with a variety of novel and well-defined morphologies, including nanospheres, nanorod bundles, and microspindles, have been prepared through a convenient modified urea-based homogeneous precipitation (UBHP) technique followed by a heat treatment. The sizes and morphologies of the YOF products could be easily modulated by changing the pH values and fluoride sources. XRD, TG-DTA, FT-IR, SEM, and TEM, as well as photoluminescence (PL) and cathodoluminescence (CL) spectra, were used to characterize the prepared samples. The YOF:Ln(3+) nanospheres show the characteristic f-f transitions of Ln(3+) (Ln = Tb, Eu, Tm, Dy, Ho, Sm) ions and give bright green, red, blue, yellow, blue-green, and yellow-orange emission, respectively, under UV light and low-voltage electron beam excitation. Furthermore, YOF:0.03Tb(3+) phosphors exhibit green luminescence with superior properties in comparison with the commercial phosphor ZnO:Zn to a degree, which is advantageous for improving display quality. Because of the simultaneous luminescence of Ln(3+) in the YOF host, the luminescence colors of YOF:Ln(3+) phosphors can be precisely adjusted by changing the doped Ln(3+) ions and corresponding concentrations, which makes these materials hold great promise for applications in field-emission displays.

DNA-Hybrid-Gated Photothermal Mesoporous Silica Nanoparticles for NIR-Responsive and Aptamer-Targeted Drug Delivery

Near-infrared light is an attractive stimulus due to its noninvasive and deep tissue penetration. Particularly, NIR light is utilized for cancer thermotherapy and on-demand release of drugs by the disruption of the delivery carriers. Here we have prepared a novel NIR-responsive DNA-hybrid-gated nanocarrier based on mesoporous silica-coated Cu1.8S nanoparticles. Cu1.8S nanoparticles, possessing high photothermal conversion efficiency under a 980 nm laser, were chosen as photothermal agents. The mesoporous silica structure could be used for drug storage/delivery and modified with aptamer-modified GC-rich DNA-helix as gatekeepers, drug vectors, and targeting ligand. Simultaneously, the as-produced photothermal effect caused denaturation of DNA double strands, which triggered the drug release of the DNA-helix-loaded hydrophilic drug doxorubicin and mesopore-loaded hydrophobic drug curcumin, resulting in a synergistic therapeutic effect. The Cu1.8S@mSiO2 nanocomposites endocytosed by cancer cells through the aptamer-mediated mode are able to generate rational release of doxorubicin/curcumin under NIR irradiation, strongly enhancing the synergistic growth-inhibitory effect of curcumin against doxorubicin in MCF-7 cells, which is associated with a strong mitochondrial-mediated cell apoptosis progression. The underlying mechanism of apoptosis showed a strong synergistic inhibitory effect both on the expression of Bcl-2, Bcl-xL, Mcl-1, and upregulated caspase 3/9 activity and on the expression level of Bak and Bax. Therefore, Cu1.8S@mSiO2 with efficient synergistic therapeutic efficiency is a potential multifunctional cancer therapy nanoplatform.

Highly uniform and monodisperse GdOF:Ln3+ (Ln = Eu, Tb, Tm, Dy, Ho, Sm) microspheres: hydrothermal synthesis and tunable-luminescence properties

GdOF:Ln(3+) (Ln = Eu, Tb, Tm, Dy, Ho and Sm) microspheres (1.5 μm) with high uniformity and monodispersity have been synthesized via a facile hydrothermal method followed by heat treatment (600 °C). X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), as well as photoluminescence (PL) and cathodoluminescence (CL) spectra are used to characterize the resulting samples. A series of controlled experiments indicate that sodium citrate (Cit(3-)) as a shape modifier introduced into the reaction system plays a critical role in the shape evolution of the final products. Furthermore, the shape and size of the products can be further manipulated by adjusting the dosage of Cit(3-) and pH values in the initial solution. The possible formation mechanism for these microspheres has been presented. Under UV light and low-voltage electron beam excitation, GdOF:Ln(3+) microspheres show the characteristic f-f transitions of Ln(3+) (Eu, Tb/Ho, Tm, Dy and Sm) ions and give bright red, green, blue, yellow and yellowish-orange emission, respectively. In addition, multicolored luminescence containing white emission have been successfully confected for co-doped GdOF:Ln(3+) phosphors by changing the doped Ln(3+) ions and adjusting their doping concentrations due to the simultaneous luminescence of Ln(3+) in the GdOF host, making these materials have potential applications in field-emission display devices.

CaGdAlO4:Tb3+/Eu3+ as promising phosphors for full-color field emission displays

Eu3+ and/or Tb3+-doped CaGdAlO4 phosphor samples were synthesized via a conventional high temperature solid-state reaction process. X-Ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) as well as cathodoluminescence (CL) spectra were used to characterize the samples. For CaGdAlO4:Tb3+, the concentration of doped Tb3+ has a significant effect on the 5D3/5D4 emission intensity due to the dipole–dipole cross-relaxation mechanism from 5D3 to 5D4. Under the 4f8 → 4f75d excitation of Tb3+ or low-voltage electron beam excitation, the CaGdAlO4:Tb3+ samples show tunable luminescence from blue to cyan and then to green with the variation of the Tb3+-doping concentration. For CaGdAlO4:Eu3+, the samples exhibit a reddish-orange emission corresponding to the 5D0,1 → 7F0,1,2,3 transitions of Eu3+. Energy transfer can take place from Tb3+ to Eu3+ when they are codoped in one host. Furthermore, for CaGdAlO4:Tb3+/Eu3+, a white emission can be realized in the single phase CaGdAlO4 host by reasonably adjusting the doping concentrations of Tb3+ and Eu3+ under low-voltage electron beam excitation. Due to the excellent PL, CL properties and good CIE chromaticity coordinates, the as-prepared Tb3+/Eu3+-doped CaGdAlO4 nanocrystalline phosphors have potential applications in field emission display devices.