Xiaojiao Kang

A magnetic, luminescent and mesoporous core–shell structured composite material as drug carrier

In this paper, hydrothermal synthesized Fe3O4 microspheres have been encapsulated with nonporous silica and a further layer of ordered mesoporous silica through a simple sol-gel process. The surface of the outer silica shell was further functionalized by the deposition of YVO4:Eu3+ phosphors, realizing a sandwich structured material with mesoporous, magnetic and luminescent properties. The multifunctional system was used as drug carrier to investigate the storage and release properties using ibuprofen (IBU) as model drug by the surface modification. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption/desorption, photoluminescence (PL) spectra, and superconducting quantum interference device (SQUID) were used to characterized the samples. The results reveal that the material shows typical ordered mesoporous characteristics, and have monodisperse spherical morphology with smooth surface and narrow size distribution. Additionally, the multifunctional system shows the characteristic emission of Eu3+ (5D0-7F(1-4)) even after the loading of drug molecules. Magnetism measurement reveals the superparamagnetic feature of the samples. Drug release test indicates that the multifunctional system shows drug sustained properties. Moreover, the emission intensities of Eu3+ in the drug carrier system increase with the released amount of drug, thus making the drug release be easily tracked and monitored by the change of the luminescence intensity.

Bioactive, luminescent and mesoporous europium-doped hydroxyapatite as a drug carrier

Bioactive, luminescent and mesoporous europium-doped hydroxyapatite (Eu:HAp) was successfully prepared through a simple one-step route using cationic surfactant as template. The obtained multifunctional hydroxyapatite was performed as a drug delivery carrier to investigate the drug storage/release properties using ibuprofen (IBU) as a model drug. The structural, morphological, textural and optical properties were well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), N(2) adsorption/desorption, and photoluminescence (PL) spectra, respectively. The results reveal that the multifunctional hydroxyapatites exhibit the typical ordered characteristics of the hexagonal mesostructure, and have rod-like morphology with the particle size of 20-40 nm in width and 100-200 nm in length. The drug storage/release test indicates that the luminescent HAp shows much similar drug loading amount and cumulative release rate to those of pure HAp. Interestingly, the IBU-loaded samples still show red luminescence of Eu(3+) ((5)D(0)-(7)F(1),(2)) under UV irradiation, and the emission intensities of Eu(3+) in the drug carrier system vary with the released amount of IBU, thus making the drug release be easily tracked and monitored by the change of the luminescence intensity.

Up-Conversion Cell Imaging and pH-Induced Thermally Controlled Drug Release from NaYF4:Yb3+/Er3+@Hydrogel Core–Shell Hybrid Microspheres

In this study, we report a new controlled release system based on up-conversion luminescent microspheres of NaYF(4):Yb(3+)/Er(3+) coated with the smart hydrogel poly[(N-isopropylacrylamide)-co-(methacrylic acid)] (P(NIPAM-co-MAA)) (prepared using 5 mol % of MAA) shell. The hybrid microspheres show bright up-conversion fluorescence under 980 nm laser excitation, and turbidity measurements show that the low critical solution temperature of the polymer shell is thermo- and pH-dependent. We have exploited the hybrid microspheres as carriers for Doxorubicin hydrochloride (DOX) due to its stimuli-responsive property as well as good biocompatibility via MTT assay. It is found that the drug release behavior is pH-triggered thermally sensitive. Changing the pH to mildly acidic condition at physiological temperature deforms the structure of the shell, causing the release of a large number of DOX from the microspheres. The drug-loaded microspheres exhibit an obvious cytotoxic effect on SKOV3 ovarian cancer cells. The endocytosis process of drug-loaded microspheres is observed using confocal laser scanning microscopy and up-conversion luminescence microscopy. Meanwhile, the as-prepared NaYF(4):Yb(3+)/Er(3+)@SiO(2)@P(NIPAM-co-MAA) microspheres can be used as a luminescent probe for cell imaging. In addition, the extent of drug release can be monitored by the change of up-conversion emission intensity. These pH-induced thermally controlled drug release systems have potential to be used for in vivo bioimaging and cancer therapy by the pH of the microenvironment changing from 7.4 (normal physiological environment) to acidic microenvironments (such as endosome and lysosome compartments) owing to endocytosis.

Ln3+ (Ln = Eu, Dy, Sm, and Er) Ion-Doped YVO4 Nano/Microcrystals with Multiform Morphologies: Hydrothermal Synthesis, Growing Mechanism, and Luminescent Properties

YVO(4) nano/microcrystals with multiform morphologies, such as nanoparticles, microdoughnut, micropancake, pillar structure, and microflower, have been synthesized via a facile hydrothermal route. A series of controlled experiments indicate that the shape and size of as-prepared architectures can be tuned effectively by controlling the reaction conditions, such as reaction time, vanadium sources, different organic additives, and the molar ratio of organic additive trisodium citrate (Cit(3-)):Y(3+). It is found that Cit(3-) as a ligand and shape modifier has the dynamic effect by adjusting the growth rate of different facets under different experimental conditions, resulting in the formation of various geometries of the final products. The possible formation mechanisms for products with diverse architectures have been presented in detail. Additionally, we systematically investigate the luminescent properties of the YVO(4):Ln(3+) (Ln = Eu, Dy, Sm, and Er). Because of an efficient energy transfer from vanadate groups to dopants, YVO(4):Ln(3+) (Ln = Eu, Dy, Sm, and Er) phosphors showed their strong characteristic emission under ultraviolet excitation and low-voltage electron beam excitation. The ability to generate YVO(4) nano/microstructures with diverse shapes, multicolor emission, and higher quantum efficiency provides a great opportunity for systematically evaluating their luminescence properties, as well as fully exploring their applications in many types of color display fields.

Colloidal synthesis and remarkable enhancement of the upconversion luminescence of BaGdF5:Yb3+/Er3+ nanoparticles by active-shell modification

BaGdF5:Yb3+/Er3+ colloidal nanoparticles (NPs) with tunable average particle diameters from 3 to 10 nm in different solvents were first prepared by thermal decomposition method. X-Ray diffraction (XRD), transmission electron microscopy (TEM) and upconversion (UC) luminescence spectra were used to characterize the resulting samples. After coating the active shell (containing Yb3+) around the BaGdF5:Yb3+/Er3+ NPs, not only their morphology and monodisperse properties were well maintained but also the relative UC luminescence intensity was enhanced remarkably. In contrast to the pure BaGdF5:Yb3+/Er3+ core, the luminescence intensity of the active-shell coated NPs can be enhanced several hundred times. Unexpectedly, the luminescence intensity of the active-core/active-shell NPs was about four times as high as that of β-NaYF4:Yb3+/Er3+ NPs under the same doping concentration and measurement conditions. Moreover, the luminescence colors of the active-core/active-shell NPs can be tuned from green to yellow by multilayer active-shell coating under 980 nm laser excitation.

Controllable and white upconversion luminescence in BaYF5:Ln3+ (Ln = Yb, Er, Tm) nanocrystals

BaYF5:Yb3+, Er3+, Tm3+ nanocrystals have been successfully synthesized via a hydrothermal process. SEM and TEM images indicate that the size of the nanocrystals is about 20 nm. Under the excitation of a 980 nm single-wavelength diode laser, BaYF5:Er3+ nanocrystals give strong green upconversion (UC) emission centered at 523 and 541 nm, which is assigned to 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+, respectively. When Yb3+ is codoped in BaYF5:Er3+, red emission around 652 nm can be observed in the emission spectrum. This emission can be assigned to the 4F9/2 → 4I15/2 transition of Er3+. The intensity ratio of the green luminescence to the red luminescence decreases with increasing Yb3+ concentration in BaYF5:Yb3+, Er3+ nanocrystals. The blue UC emissions of BaYF5:Yb3+, Tm3+ nanocrystals appeared near 464 and 480 nm and are assigned to the 1D2 → 3F4 and 1G4 → 3H6 transitions of Tm3+, respectively. Based on the generation of red, green, and blue emissions, the BaYF5:Yb3+, Er3+, Tm3+ nanocrystals can produce different colors, including white, by controlling the doping concentration of Yb3+ in the BaYF5 nanocrystals. The BaYF5:40%Yb3+, 0.5%Er3+, 0.5%Tm3+nanocrystals show proper intensities of blue, green, and red emissions, which result in the production of white light (CIE: x = 0.346, y = 0.336).

Tunable Luminescence and Energy Transfer properties of Sr3AlO4F:RE3+ (RE = Tm/Tb, Eu, Ce) Phosphors

Sr(3)AlO(4)F:RE(3+) (RE = Tm/Tb, Eu, Ce) phosphors were prepared by the conventional solid-state reaction. X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), photoluminescence (PL) spectra, as well as lifetimes were utilized to characterize samples. Under the excitation of UV light, Sr(3)AlO(4)F:Tm(3+), Sr(3)AlO(4)F:Tb(3+), and Sr(3)AlO(4)F:Eu(3+) exhibit the characteristic emissions of Tm(3+) ((1)D(2)→(3)F(4), blue), Tb(3+) ((5)D(4)→(7)F(5), green), and Eu(3+) ((5)D(0)→(7)F(2), red), respectively. By adjusting the doping concentration of Eu(3+) ions in Sr(3)AlO(4)F:0.10Tm(3+), 0.10Tb(3+), zEu(3+), a white emission in a single composition was obtained under the excitation of 360 nm, in which an energy transfer from Tb(3+) to Eu(3+) was observed. For Sr(3)AlO(4)F:Ce(3+),Tb(3+) samples, the energy transfer from Ce(3+) to Tb(3+) is efficient and demonstrated to be a resonant type via a dipole-quadrupole interaction by comparing the experimental data and theoretical calculation. Furthermore, the critical distance of the Ce(3+) and Tb(3+) ions has also been calculated to be 9.05 Å. The corresponding luminescence and energy transfer mechanisms have been proposed in detail. These phosphors might be promising for use in near-UV LEDs.

Hydrothermal Derived LaOF:Ln3+ (Ln = Eu, Tb, Sm, Dy, Tm, and/or Ho) Nanocrystals with Multicolor-Tunable Emission Properties

A series of LaOF:Ln(3+) (Ln = Eu, Tb, Sm, Dy, Tm, and/or Ho) nanocrystals with good dispersion have been successfully prepared by the hydrothermal method followed a heat-treatment process. Under ultraviolet radiation and low-voltage electron beam excitation, the LaOF:Ln(3+) nanocrystals show the characteristic f-f emissions of Ln(3+) (Ln = Eu, Tb, Sm, Dy, Tm, or Ho) and give red, blue-green, orange, yellow, blue, and green emission, respectively. Moreover, there exists simultaneous luminescence of Tb(3+), Eu(3+), Sm(3+), Dy(3+), Tm(3+), or Ho(3+) individually when codoping them in the single-phase LaOF host (for example, LaOF:Tb(3+), Eu(3+)/Sm(3+); LaOF:Tm(3+), Dy(3+)/Ho(3+); LaOF:Tm(3+), Ho(3+), Eu(3+) systems), which is beneficial to tune the emission colors. Under low-voltage electron beam excitation, a variety of colors can be efficiently adjusted by varying the doping ions and the doping concentration, making these materials have potential applications in field-emission display devices. More importantly, the energy transfer from Tm(3+) to Ho(3+) in the LaOF:Tm(3+), Ho(3+) samples under UV excitation was first investigated and has been demonstrated to be a resonant type via a quadrupole-quadrupole mechanism. The critical distance (R(Tm-Ho)) is calculated to be 28.4 Å. In addition, the LaOF:Tb(3+) and LaOF:Tm(3+) phosphors exhibit green and blue luminescence with better chromaticity coordinates, color purity, and higher intensity compared with the commercial green phosphor ZnO:Zn and blue phosphor Y(2)SiO(5):Ce(3+) to some extent under low-voltage electron beam excitation.

Tunable luminescence in Ce3+, Mn2+-codoped calcium fluorapatite through combining emissions and modulation of excitation: a novel strategy to white light emission

The Ce3+, Mn2+-codoped calcium fluorapatite [Ca5(PO4)3F, FAP] nanorods were prepared by a simple hydrothermal method. SEM and TEM images indicate that the FAP : Ce3+, Mn2+ sample consists of nanorods with lengths around 30–70 nm and diameters around 20 nm, respectively. The as-obtained FAP nanorods show an intense bright blue emission (centered at 432 nm, lifetime 7.5 ns) arising from CO2˙− radical impurities in the crystal lattice under UV light irradiation. In addition, codoped with Ce3+ and Mn2+, the as-synthesized FAP : Ce3+, Mn2+ sample shows the tunable luminescence from blue to white to yellow by the variation of excitation UV light. The emission spectra of the as-synthesized FAP : Ce3+, Mn2+ sample show three broad bands, which are associated with the CO2˙− radical impurities (blue emission), Ce3+ ions (ultraviolet emission), and Mn2+ ions (yellow emission), respectively. The coexistence of three broad emissions results in the bright white light directly under suitable excitation wavelength. The combination emissions of impurities and metal activator ions may provide a novel strategy to obtain white light and tunable luminescence.

Doxorubicin conjugated NaYF4:Yb3+/Tm3+ nanoparticles for therapy and sensing of drug delivery by luminescence resonance energy transfer

In this study, we report an anticancer drug delivery system based on doxorubicin (DOX)-conjugated NaYF(4):Yb(3+)/Tm(3+) nanoparticles. The as-synthesized nanoparticles consist of uniform spherical nanoparticles with an average diameter of 25 nm. The drug delivery system demonstrates the ability to release DOX by cleavage of the hydrazone bond in mildly acidic environments. The spectra overlap between emission of donor NaYF(4):Yb(3+)/Tm(3+) nanoparticles at 452 nm ((1)D(2)→(3)F(4)) and 477 nm ((1)G(4)→(3)H(6)) and the broad absorbance of acceptor DOX centered at around 480 nm enables energy transfer to occur between the nanoparticles and DOX. The quenching and recovery of the up-conversion luminescence of NaYF(4):Yb(3+)/Tm(3+) by DOX due to luminescence resonance energy transfer (LRET) mechanism are applied as optical probe to confirm the DOX conjunction and monitor the release of DOX. The DOX-conjugated NaYF(4):Yb(3+)/Tm(3+) nanoparticles exhibit an obvious cytotoxic effect on SKOV3 ovarian cancer cells via MTT assay. Meanwhile, the endocytosis process of DOX-conjugated NaYF(4):Yb(3+)/Tm(3+) nanoparticles by SKVO3 cells was demonstrated through confocal laser scanning microscopy (CLSM), flow cytometry and ICP-OES. Such drug delivery system, which combines pH-triggered drug-release and up-converting nanoparticles-based LRET property, has excellent potential applications in cancer therapy and smart imaging.