Synthesis of ultrastable eu‐complex/polystyrene composite luminescent nanoparticles using a solvent swelling method

Nanoparticles composed of Eu‐complex, Eu(TTA)₃Phen, and polystyrene (PS) were successfully synthesized through an improved solvent swelling method. The unstable Eu(TTA)₃Phen could be protected by the hydrophobic shell of PS nanoparticles. This method is very appropriate to embed unstable luminescent molecules into polymer nanoparticles. The as‐synthesized luminescent PS nanoparticles have been turned out to be water‐dispersible, strong red luminescent, ultrastable in strong acid and alkali, and luminescence lifetime enhanced. A cell imaging assay was further carried out and strong luminescent signal could be obtained, which showed that the as‐synthesized luminescent Eu‐complex/PS nanoparticles are a good candidate to be used as luminescent nanoparticles in tumor cell detection. This solvent swelling method is simple, easy to scale‐up, and has great potential in the preparation of other luminescent nanoparticles. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Water-soluble NaYF4:Yb/Er upconversion nanophosphors: Synthesis,characteristics and application in bioimaging

Water-soluble and citrate (cit) coated rare-earth upconversion nanophosphors (UCNPs) were prepared by an efficient surface ligand exchange of the oleic acid capped hydrophobic UCNPs in diethylene glycol (DEG) at high temperature. The successful surface ligand exchange of the UCNPs with citrate was confirmed by Fourier-transform infrared (FTIR) spectroscopy. Further characterizations such as TEM and XRD showed that the ligand exchange reaction had no obvious influence on chemical properties of UCNPs, such as morphology and crystallization. Furthermore, bright UC luminescence was observed when UCNPs-labeled cells were excited with 980nm near-infrared (NIR) light proving that Cit-UCNPs can be used as non-specific labels for imaging HeLa cells. These results indicate that the Cit-UCNPs are a promising candidate for use as bioimaging probes.     

上转换发光材料在不同防伪领域的研究进展Q

稀土上转换纳米粒子（UCNPs）能够吸收低能量的红外光并转换为高能量的紫外或可见光,其具有自体发光背景低、发光颜色可调、荧光寿命长和光稳定性好等优异的光学性能,此外,其还具有可加工性高、表面功能化便捷等特点,因而如今已经成为了荧光防伪技术的研究前沿和研究热点,应用前景十分广泛。本文综述了UCNPs的发光机制和一系列制备方法并分析优缺点,阐述了近年来其在标签、图案、编码等荧光防伪领域应用的相关优秀研究成果。进一步地,还探讨了UCNPs在荧光防伪领域应用上所存在的问题和面临的挑战,提出了未来可能的发展方向。     

NIR-Triggered Generation of Reactive Oxygen Species and Photodynamic Therapy Based on Mesoporous Silica-Coated LiYF4 Upconverting Nanoparticles

To date, the increase in reactive oxygen species (ROS) production for effectual photodynamic therapy (PDT) treatment still remains challenging. In this study, a facile and effective approach is utilized to coat mesoporous silica (mSiO₂) shell on the ligand-free upconversion nanoparticles (UCNPs) based on the LiYF₄ host material. Two kinds of mesoporous silica-coated UCNPs (UCNP@mSiO₂) that display green emission (doped with Ho³⁺) and red emission (doped with Er³⁺), respectively, were successfully synthesized and well characterized. Three photosensitizers (PSs), merocyanine 540 (MC 540), rose bengal (RB), and chlorin e6 (Ce6), with the function of absorption of green or red emission, were selected and loaded into the mSiO₂ shell of both UCNP@mSiO₂ nanomaterials. A comprehensive study for the three UCNP@mSiO₂/PS donor/acceptor pairs was performed to investigate the efficacy of fluorescence resonance energy transfer (FRET), ROS generation, and in vitro PDT using a MCF-7 cell line. ROS generation detection showed that as compared to the oleate-capped and ligand-free UCNP/PS pairs, the UCNP@mSiO₂/PS nanocarrier system demonstrated more pronounced ROS generation due to the UCNP@mSiO₂ nanoparticles in close vicinity to PS molecules and a higher loading capacity of the photosensitizer. As a result, the three LiYF₄ UCNP@mSiO₂/PS nanoplatforms displayed more prominent therapeutic efficacies in PDT by using in vitro cytotoxicity tests.     

上转换发光材料在不同防伪领域的研究进展Q

稀土上转换纳米粒子(UCNPs)能够吸收低能量的近红外光并转换为高能量的紫外或可见光,具有自体发光背景低、发光颜色可调、荧光寿命长和光稳定性好等优异的光学性能,还具有可加工性高、表面功能化便捷等特点,已成为荧光防伪技术的研究前沿和研究热点,应用前景广泛.该文综述了UCNPs的发光机制和制备方法,阐述了近年来其在标签、图案、编码等荧光防伪领域应用的相关研究成果.进一步地探讨了UCNPs在荧光防伪领域应用上所存在的问题和面临的挑战,提出了未来可能的发展方向.     

Monodisperse NaYbF4:Tm3+/NaGdF4 core/shell nanocrystals with near-infrared to near-infrared upconversion photoluminescence and magnetic resonance properties

We report core/shell NaYbF(4):Tm(3+)/NaGdF(4) nanocrystals to be used as probes for bimodal near infrared to near infrared (NIR-to-NIR) upconversion photoluminescence (UCPL) and magnetic resonance (MR) imaging. The NaYbF(4):Tm(3+) nanocrystals were previously reported to produce the intense NIR-to-NIR UCPL peaked at ～800 nm under excitation at ～975 nm. We have found that the growth of a NaGdF(4) shell on surface of the NaYbF(4):Tm(3+) nanocrystals results in the increase in the intensity of UCPL of Tm(3+) ions by about 3 times. Unlike biexponential PL decay of NaYbF(4):Tm(3+) nanocrystals, the PL decay of NaYbF(4):Tm(3+)/NaGdF(4) core/shell nanocrystals is single exponential and of longer lifetime due to the suppression of surface quenching effects for Tm(3+) PL. The growth of a NaGdF(4) shell on surface of the NaYbF(4):Tm(3+) nanocrystals also provides high MR relaxivity from paramagnetic Gd(3+) ions contained in the shell. The T1-weighted MR signal of the (NaYbF(4):2% Tm(3+))/NaGdF(4) nanoparticles was measured to be about 2.6 mM(-1)s(-1). Due to the combined presence of efficient optical and MR imaging capabilities, nanoprobes based on NaYbF(4):Tm(3+)/NaGdF(4) fluoride nanophosphors can be considered as a promising platform for simultaneous bimodal PL and MR bioimaging.     

Dual-modal fluorescent/magnetic bioprobes based on small sized upconversion nanoparticles of amine-functionalized BaGdF5:Yb/Er

A new type of BaGdF(5):Yb/Er nanoprobe for dual-modal fluorescent and magnetic resonance imaging (MRI) is demonstrated. Water soluble and amine-functionalized BaGdF(5):Yb/Er nanoparticles (NPs) with average size of about 10 nm were synthesized by a facile one-pot hydrothermal method. The in vitro up-converted emission of BaGdF(5):Yb/Er NPs is observed in HeLa cells with near-infrared excitation at 980 nm and served as a fluorescent label. In addition, the cytotoxicity assay in HeLa cells shows low cell toxicity of the amine-functionalized BaGdF(5):Yb/Er NPs. Moreover, these BaGdF(5) NPs exhibit excellent intrinsic paramagnetic properties and enhanced T(1)-weighted MRI images with increased concentrations of BaGdF(5) NPs. Therefore, these results suggest that the amine-functionalized BaGdF(5) NPs with an optimized size and low cell toxicity are promising dual-modal bioprobes for optical bioimaging and MRI.     

Morphology and phase control of fluorides nanocrystals activated by lanthanides with two-model luminescence properties

The morphology, size and phase control of luminescent fluoride nanocrystals through doping has become a new research hotspot due to their improved properties. In this work, Yb(3+) ions, as one of the most efficient sensitizers for various lanthanide activators, were doped in NaGd(Y)F(4) nanocrystals. The results show that no obvious influence was observed for Yb(3+)-doped NaYF(4) nanocrystals, while the influence of Yb(3+) doping on NaGdF(4) nanocrystals was remarkable. The NaGd(1-x)Yb(x)F(4) nanocrystals were synthesized by a hydrothermal route and had a morphology of rice-like nanorods. By controlling the synthesis parameters, the average size and slenderness of the nanocrystals increased gradually with addition of Yb(3+) ions. In contrast, the NaGd(1-x)Yb(x)F(4) nanocrystals maintained a hexagonal phase, which is more beneficial for application as a luminescent host, until the content of Yb(3+) ions reached x = 0.9. The growth and transformation mechanism of NaGd(1-x)Yb(x)F(4) nanocrystals was proposed to be a result of the competition between ion diffusion and an Oswald ripening process. Photoluminescence (PL) spectra confirm the efficient up-conversion and near-infrared (NIR) two-model luminescence properties of Er(3+) (Tm(3+)) activated NaGd(Y)(1-x)Yb(x)F(4) nanocrystals. Simulated analysis results indicate that a colloidal solution of mixed luminescent nanocrystals is expected to find application as the activated medium of three dimensional displays and a broadband optical amplifier.     

Functionalization of Photosensitized Silica Nanoparticles for Advanced Photodynamic Therapy of Cancer

BODIPY dyes have recently attracted attention as potential photosensitizers. In this work, commercial and novel photosensitizers (PSs) based on BODIPY chromophores (haloBODIPYs and orthogonal dimers strategically designed with intense bands in the blue, green or red region of the visible spectra and high singlet oxygen production) were covalently linked to mesoporous silica nanoparticles (MSNs) further functionalized with PEG and folic acid (FA). MSNs approximately 50 nm in size with different functional groups were synthesized to allow multiple alternatives of PS-PEG-FA decoration of their external surface. Different combinations varying the type of PS (commercial Rose Bengal, Thionine and Chlorine e6 or custom-made BODIPY-based), the linkage design, and the length of PEG are detailed. All the nanosystems were physicochemically characterized (morphology, diameter, size distribution and PS loaded amount) and photophysically studied (absorption capacity, fluorescence efficiency, and singlet oxygen production) in suspension. For the most promising PS-PEG-FA silica nanoplatforms, the biocompatibility in dark conditions and the phototoxicity under suitable irradiation wavelengths (blue, green, or red) at regulated light doses (10–15 J/cm²) were compared with PSs free in solution in HeLa cells in vitro.     

Photodynamic Therapy and Multi-Modality Imaging of Up-Conversion Nanomaterial Doped with AuNPs

Two key concerns exist in contemporary cancer chemotherapy in clinic: limited therapeutic efficiency and substantial side effects in patients. In recent years, researchers have been investigating a revolutionary cancer treatment technique, and photodynamic therapy (PDT) has been proposed by many scholars. A drug for photodynamic cancer treatment was synthesized using the hydrothermal method, which has a high efficiency to release reactive oxygen species (ROS). It may also be utilized as a clear multi-modality bioimaging platform for photoacoustic imaging (PAI) due to its photothermal effect, computed tomography (CT), and magnetic resonance imaging (MRI). When compared to single-modality imaging, multi-modality imaging delivers far more thorough and precise details for cancer diagnosis. Furthermore, Au-doped up-conversion nanoparticles (UCNPs) have an exceptionally high luminous intensity. The Au-doped UCNPs, in particular, are non-toxic to tissues without laser at an 808 nm wavelength, endowing the as-prepared medications with outstanding therapeutic efficacy but exceptionally low side effects. These findings may encourage fresh effective imaging-guided approaches to meet the goal of photodynamic cancer therapy to be created.     

Viscoelasticity of shell-crosslinked core–shell nanoparticles filled polystyrene melt

Shell-crosslinked core–shell nanoparticles (SCCSN) of 63–104 nm in diameter and containing 79.1 wt% crosslinked polystyrene (PS) shell of 16.5–37.0 nm in thickness were prepared by miniemulsion polymerization of styrene in the presence of silane modified nanosilica. The PS shell was crosslinked using divinyl benzene in order to anchor the shell on the nanoparticle surface, to segregate the silica core from the matrix and to avoid entanglement between the shell PS and the matrix macromolecules in SCCSN filled PS composites. Steady and dynamic rheologies of SCCSN filled PS were compared with bare silica filled PS. The SCCSN filled PS composites exhibited exceedingly good rheological stability than silica filled ones during annealing. Both bare silica and SCCSN introduced a non-terminal dynamic rheology while they did not introduce additional mechanism responsible for origination of nonlinear steady flow except for macromolecular disentanglement of the PS matrix. The reinforcement of SCCSN to PS was related to the silica core even though the crosslinked shell could effectively eliminate filler aggregation as the case of silica filled PS.     

Graphene Quantum Dots Modified Upconversion Nanoparticles for Photodynamic Therapy

Photodynamic therapy (PDT), as a novel technique, has been extensively employed in cancer treatment by utilizing reactive oxygen species (ROS) to kill malignant cells. However, most photosensitizers (PSs) are short of ROS yield and affect the therapeutic effect of PDT. Thus, there is a substantial demand for the development of novel PSs for PDT to advance its clinical translation. In this study, we put forward a new strategy for PS synthesis via modifying graphene quantum dots (GQDs) on the surface of rare-earth elements doped upconversion nanoparticles (UCNPs) to produce UCNPs@GQDs with core-shell structure. This new type of PSs combined the merits of UCNPs and GQDs and produced ROS efficiently under near-infrared light excitation to trigger the PDT process. UCNPs@GQDs exhibited high biocompatibility and obvious concentration-dependent PDT efficiency, shedding light on nanomaterials-based PDT development.     

Bio-functionalization of ligand-free upconverting lanthanide doped nanoparticles for bio-imaging and cell targeting

We report on the functionalization of ligand-free NaGdF(4):Er(3+), Yb(3+) upconverting nanoparticles with heparin and basic fibroblast growth factor (bFGF). These upconverting nanoparticles are used to obtain high-contrast images of HeLa cells. These images reveal that the heparin-bFGF functionalized nanoparticles show specific binding to the cell membrane.     

Development of biocompatible NaGdF4: Er3+, Yb3+ upconversion nanoparticles used as contrast agents for bio‐imaging

Upconversion nanoparticles with special fluorescence and magnetic properties have been considered an alternative contrast agent for multiple bio‐imaging techniques. It is important to understand the effects of the surface properties and dosage of upconversion nanoparticles on both the magnetic resonance (MRI) image and the photoluminescence spectrum. Here, NaGdF₄: Er³⁺, Yb³⁺ upconversion nanoparticles (UCNPs) modified with amine functional group were produced through a one‐pot thermal decomposition. The average length of the cubic UCNPs is estimated at 53 ±13 nm. The effect of the dosage of amine modified UCNPs on the MRI image is investigated. The T₁ and T₂ relaxivities of the amine modified UCNPs in agarose gel at 3 T are r₁ = 6.79 ±0.14 and r₂ = 17.0 ±0.18 (mmol/L)^?1 s^?1, which are comparable to the relaxivities of commercially available MRI contrast agents. In addition, the photoluminescence of the amine modified UCNPs at low concentrations < 150 µg/mL are further investigated with the excitation wavelength (λ_ex) at 980 nm. The internalization of the amine modified UCNPs cultured with human umbilical vascular endothelial cells (HUVEC) is observed by the fluorescence imaging. Meanwhile, T₁‐weighted MRI imaging of HUVEC cells treated with amine modified UCNPs at 10 µg/mL can be obtained. No significant toxic effect on cells is found when the concentration of the amine modified UCNPs is < 300 µg/mL. This study indicates that a low concentration of amine‐modified NaGdF₄: Er³⁺, Yb³⁺ UCNPs can be used as the contrast agent for both fluorescence imaging and magnetic resonance imaging.     

Preparation of core–shell poly(acrylic acid)/polystyrene/SiO2 hybrid microspheres

Core–shell poly(acrylic acid)/polystyrene/SiO₂ (PAA/PS/SiO₂) hybrid microspheres were prepared by dispersion polymerization with three stages in ethanol and ethyl acetate mixture medium. Using vinyltriethoxysilane (VTEOS) as silane agent, functional silica particles structured vinyl groups on surfaces were prepared by hydrolysis and polycondensation of tetraethoxysilane and VTEOS in core stage. Then, the silica particles were used as seeds to copolymerize with styrene and acrylic acid sequentially in shell stage I and stage II to form PAA/PS/SiO₂ hybrid microspheres. Transmission electron microscope results show that most PAA/PS/SiO₂ hybrid microspheres are about 40 nm in diameter, and the silica cores are about 15 nm in diameter, which covered with a layer of PS about 7.5‐nm thick and a layer of PAA about 5‐nm thick. This core–shell structure is also conformed by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and differential scanning calorimetry. FTIR results show that silica core, PS shell, and PAA outermost shell are bonded by covalents. In the core–shell PAA/PS/SiO₂ hybrid microsphere, the silica core is rigidity, and the PAA outermost shell is polarity, while the PS layer may work as lubricant owning to its superior processing rheological property in polymer blending. These core–shell PAA/PS/SiO₂ hybrid microspheres have potential as new materials for polar polymer modification. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1729–1733, 2006     

Controlled synthesis and optical spectroscopy of lanthanide-doped KLaF₄ nanocrystals

KLaF(4), as a good host matrix for trivalent lanthanide (Ln(3+)) ions to fabricate upconversion (UC) or downconversion (DC) phosphors, has been rarely reported. Herein, monodisperse (～10 nm) cubic-phase Ln(3+)-doped KLaF(4) nanocrystals (NCs) were synthesized via a facile thermal decomposition method. Upon excitation at 980 nm, UC luminescence properties of KLaF(4):Ln(3+)/Yb(3+) (Ln = Tm, Ho, Er) NCs were comprehensively surveyed. Particularly, after coating an inert KLaF(4) shell, the green and red UC luminescence intensity of KLaF(4):Er(3+)/Yb(3+) NCs was enhanced ～35 times, and the corresponding UC lifetimes of (4)S(3/2) and (4)F(9/2) levels of Er(3+) were observed significantly prolonged from 42 and 68 μs in core-only NCs to 87 and 136 μs in core/shell counterparts. Furthermore, intense DC luminescence was also achieved in Ce(3+)/Tb(3+) and Eu(3+) doped KLaF(4) NCs, with absolute quantum yields of 39.8% (Tb(3+)) and 17.3% (Eu(3+)). The luminescence lifetimes of (5)D(0) (Eu(3+)) and (5)D(4) (Tb(3+)) were determined to be 4.2 and 4.7 ms, respectively. Water-soluble Ln(3+)-doped KLaF(4) NCs featuring excellent monodispersion, long luminescence lifetime, and high UC/DC efficiency may have versatile and promising applications as luminescent nano-biolabels.     

Exploring the Elastic Behavior of Core–shell Organic–Inorganic Spherical Particles by AFM Indentation Experiments

Monodispersed polystyrene (PS)-silica core–shell composite particles were synthesized via the hydrolysis and condensation of tetraethoxysilane (TEOS) on PS colloids at acidic medium. The thickness of silica coating was controlled by the amount of the addition of TEOS during the shell growth process. Transmission electron microscopy results confirmed that a continuous amorphous network of homogenous coating of silica was formed on the PS colloids. After coating by silica, the particle diameter increased from ca. 221 nm for uncoated PS cores to ca. 243–286 nm for PS-silica composite particles observed by scanning electron microscopy, indicating that the silica shell thickness was 11–32 nm. The elastic behavior of the obtained products was investigated by means of atomic force microscopy. The elastic moduli of samples were calculated by fitting the retract curves in force-separation plots based on the Hertzian contact model. The average moduli were 4–8 GPa for the PS-silica composite particles which were much lower than the that of the pure silica (72–75 GPa) and closed to that of the PS cores (2.1 ± 0.5 GPa). The elastic moduli of the PS-silica hybrids increased with increasing of silica shell thickness, suggesting that the elasticity of the PS-silica composite particles might be attributed to the PS cores and the silica shell was stiffening the polymer cores. These results provide a basis for exploring the mechanical properties of core–shell PS-silica hybrids in the application of novel abrasives for chemical mechanical polishing.     

Lanthanide ion-doped GdPO4 nanorods with dual-modal bio-optical and magnetic resonance imaging properties

Here, dual-modal bioprobes for combined optical and magnetic resonance (MR) imaging are reported. Gadolinium orthophosphate (GdPO(4)) nanorods co-doped with light-emitting lanthanide ions have been successfully prepared through a hydrothermal method. An efficient downconversion luminescence from Ce/Tb or Eu doped GdPO(4) nanorods and upconversion luminescence from Yb/Er co-doped GdPO(4) nanorods are observed, respectively, which offers the optical modality for the nanoprobes. Notably, we first report the upconversion phenomenon based on the GdPO(4) matrix under 980 nm near infrared irradiation. The possibility of using these nanoprobes with downconversion and upconversion luminescent emissions for optical cell imaging is also demonstrated. Furthermore, these Gd(3+)-containing nanophosphors show good positive signal-enhancement ability when performed under a 4.7 T MR imaging scanner, indicating they have potential as T(1) MR imaging contrast agents. Thus, nanoprobes based on GdPO(4) nanophosphors are shown to provide the dual modality of optical and MR imaging.     

Effect of Cerenkov Radiation-Induced Photodynamic Therapy with 18F-FDG in an Intraperitoneal Xenograft Mouse Model of Ovarian Cancer

Ovarian cancer (OC) metastases frequently occur through peritoneal dissemination, and they contribute to difficulties in treatment. While photodynamic therapy (PDT) has the potential to treat OC, its use is often limited by tissue penetration depth and tumor selectivity. Herein, we combined Cerenkov radiation (CR) emitted by ¹⁸F-FDG accumulated in tumors as an internal light source and several photosensitizer (PS) candidates with matched absorption bands, including Verteporfin (VP), Chlorin e6 (Ce6) and 5′-Aminolevulinic acid (5′-ALA), to evaluate the anti-tumor efficacy. The in vitro effect of CR-induced PDT (CR-PDT) was evaluated using a cell viability assay, and the efficiency of PS was assessed by measuring the singlet oxygen production. An intraperitoneal ES2 OC mouse model was used for in vivo evaluation of CR-PDT. Positron emission tomography (PET) imaging and bioluminescence-based imaging were performed to monitor the biologic uptake of ¹⁸F-FDG and the therapeutic effect. The in vitro studies demonstrated Ce6 and VP to be more effective PSs for CR-PDT. Moreover, VP was more efficient in the generation of singlet oxygen and continued for a long time when exposed to fluoro-18 (¹⁸F). Combining CR emitted by ¹⁸F-FDG and VP treatment not only significantly suppressed tumor growth, but also prolonged median survival times compared to either monotherapy.     

Synthesis of NaYF4:Yb3+, Er3+ upconversion nanoparticles in normal microemulsions

An interface-controlled reaction in normal microemulsions (water/ethanol/sodium oleate/oleic acid/n-hexane) was designed to prepare NaYF4:Yb3+, Er3+ upconversion nanoparticles. The phase diagram of the system was first studied to obtain the appropriate oil-in-water microemulsions. Transmission electron microscopy and X-ray powder diffractometer measurements revealed that the as-prepared nanoparticles were spherical, monodisperse with a uniform size of 20 nm, and of cubic phase with good crystallinity. Furthermore, these nanoparticles have good dispersibility in nonpolar organic solvents and exhibit visible upconversion luminescence of orange color under continuous excitation at 980 nm. Then, a thermal treatment for the products was found to enhance the luminescence intensity. In addition, because of its inherent merit in high yielding and being economical, this synthetic method could be utilized for preparation of the UCNPs on a large scale.