Biofunctionalization of Fluorescent Rare-Earth-Doped Lanthanum Phosphate Colloidal Nanoparticles

Optical properties and luminescence dynamics of Eu3+-doped terbium orthophosphate nanophosphors

The development of luminescent inorganic nanocrystals (NCs) doped with rare-earth (RE) ions has attracted increasing interest owing to their distinct optical properties and versatile applications in time-resolved bioassays, multiplex biodetection, DNA hybridization and bioimaging. Hexagonal TbPO4:Eu3+ NCs (10-30 nm) were synthesized via a facile hydrothermal method assisted with oleic acid (OA) surfactants, which exhibit tunable emissions from green to red by varying the concentration of Eu3+. The Tb3+-to-Eu3+ energy transfer efficiency observed reaches up to 94%. Different from their bulk counterparts, a new interface-state band (316 nm) in addition to the commonly observed spin-forbidden 4f-5d transition band (265 nm) of Tb3+ was found to be dominant in the excitation spectrum of NCs due presumably to the formation of surface TbPO4/OA complexes, which provides an additional excitation antenna in practical utilization. Two kinds of luminescence sites of Eu3+ in TbPO4 NCs, with the site symmetry of C2 or C1, were identified based on the emission spectra at 10 K and room temperature. Furthermore, the photoluminescence (PL) dynamics of Tb3+ ions in pure TbPO4 NCs have been revealed. Compared to the exponential PL decay in bulk counterparts induced by very fast energy migration, the non-exponential decay from 5D4 of Tb3+ in TbPO4 NCs is mainly attributed to the diffusion-limited energy migration due to more rapid energy transfer from Tb3+ to defects than the energy migration among Tb3+.

Simultaneous synthesis and functionalization of water-soluble up-conversion nanoparticles for in-vitro cell and nude mouse imaging

Water-solubility and biocompatibility are prerequisites for rare-earth up-converting nanophosphors applied to biological imaging. In this work, we have developed a facile and one-step synthesis technique, through which water-soluble NaYF(4): Yb(3+), Er(3+) nanoparticles (NPs) with functional groups including 3-mercaptopropionic acid, 6-aminocaproic acid and poly(ethylene glycol)methyl ether on their surface can be directly prepared without any further surface treatment. Some inorganic salts will be selected as starting materials, water and some low toxic organic agents have been used as reaction media, which differs from earlier works. Structural and up-converting fluorescence are characterized by a variety of techniques. Cell uptake and in-vitro imaging of the as-synthesized NPs have been investigated using a multiphoton con-focal laser scanning microscope with a near-infrared excitation source. Internalization of the bare and functionalized NPs in human lung carcinoma A549 and human cervical carcinoma HeLa cells are studied at a nanoparticle loading of 10 µg mL(-1) over an exposure period from 30 min to 24 h. The cytotoxicity of modified NPs in HeLa cells is found to be low. In addition, the feasibility of the NPs in animal imaging has been demonstrated by subcutaneously injecting these NPs into nude mouse. The results indicated that our directly synthesized NPs coated with various functional groups are promising as bio-imaging agents due to their easy uptake, long lasting, low cytotoxicity, emissive in various human carcinoma cell lines and small animals through up-conversion with near-infrared excitation.

Purification of biomimetic apatite-based hybrid colloids intended for biomedical applications: A dialysis study

The field of nanobiotechnology has lately attracted much attention both from therapeutic and diagnosis viewpoints. Of particular relevance is the development of colloidal formulations of biocompatible nanoparticles capable of interacting with selected cells or tissues. In this context, the purification of such nanoparticle suspensions appears as a critical step as residues of unreacted species may jeopardize biological and medical outcomes, and sample purity is thus increasingly taken into account by regulatory committees. In the present work, we have investigated from a physico-chemical point of view the purification by dialysis of recently developed hybrid colloids based on biomimetic nanocrystalline apatites intended for interacting with cells. Both Eu-doped (2mol.% relative to Ca) and Eu-free suspensions were studied. The follow-up of the dialysis process was carried out by way of FTIR, TEM, XRD, pH and conductivity measurements. Mathematical modelling of conductivity data was reported. The effects of a change in temperature (25 and 45°C), dialysis medium, and starting colloid composition were evaluated and discussed. We show that the dialysis method is a well-adapted and cheap technique to purify such mineral-organic hybrid suspensions in view of biomedical applications, and we point out some of the characterization techniques that may prove helpful for following the evolution of the purification process with time.

Aptamer-functionalized magnetic nanoparticle-based bioassay for the detection of ochratoxin A using upconversion nanoparticles as labels

A sensitive luminescent bioassay for the detection of ochratoxin A (OTA), a small molecular mycotoxin, was developed using aptamer-conjugated magnetic nanoparticles (MNPs) as the recognition and concentration element and upconversion nanoparticles (UCNPs) as highly sensitive labels. The bioassay system was fabricated by immobilizing aptamer DNA 1 sequence onto the surface of Fe(3)O(4) MNPs, which were implemented to capture and concentrate OTA from bulk samples. The aptamer DNA 1 sequence then hybridized with UCNPs modified with DNA 2 sequence, which could dissociate from DNA 1 and result in a decreased luminescent signal when aptamer DNA 1 recognized and bound to target OTA. Under the optimal conditions, the decreased luminescent intensity (ΔI) is proportional to the concentration of OTA in the range of 1 × 10(-13) to 1 × 10(-9) g mL(-1) with a detection limit of 1 × 10(-13) g mL(-1). The proposed method then was successfully applied to measure OTA in naturally contaminated maize samples and validated by a commercially available enzyme-linked immunosorbent assay (ELISA) method. Benefiting from the magnetic separation and concentration effect of MNPs, the high sensitivity of UCNPs, as well as the selectivity and stability of the aptamer, the present upconversion luminescent bioassay offers a promising approach for the screening of small molecular mycotoxins because it is simple, rapid, highly sensitive, specific, does not require sample pre-concentration and lacks interference from autofluorescence of other biomolecules.

Photoluminescence, cytotoxicity and in vitro imaging of hexagonal terbium phosphate nanoparticles doped with europium

Luminescent TbPO4 nanoparticles were synthesized via a citric-acid-mediated hydrothermal route. Eu3+ doping of TbPO4 enables an efficient Tb3+-to-Eu3+ energy transfer, leading to a four-fold increase of the absolute emission quantum yield (QY), compared to that of undoped TbPO4. To check the potential of biological use, we conducted in vitro biological experiments on human cervical carcinoma HeLa cells incubated with TbPO4:Eu nanoparticles. TbPO4:Eu nanoparticles can be successfully internalized into the cells, and they show bright intracellular luminescence and very low cytotoxicity. Photoluminescence intensity dependence upon time demonstrates that Eu3+-doped TbPO4 nanoparticles are highly resistant to photobleaching. Our present work represents a demonstration of the use of rare-earth-based nanocrystals as a biological labeling agent because they combine several advantages including high emission quantum yield, long luminescence lifetime, low cytotoxicity and high photostability.

Fluorescent sensing of colloidal CePO4:Tb nanorods for rapid, ultrasensitive and selective detection of vitamin C

Vitamin C is an essential biological molecule for living organisms. The detection of vitamin C is always required due to its wide use in chemical, biological and pharmaceutical engineering. Here, we established a novel sensing system for rapid, ultrasensitive and highly selective detection of vitamin C based on a 'turn-on' fluorescent method. The turn-on fluorescent sensing system was built up of a colloidal CePO(4):Tb nanocrystalline solution with its fluorescence quenched by KMnO(4). The addition of vitamin C leads to a linear increase of fluorescence. The sensing principle of nanocrystalline CePO(4):Tb is based on a redox reaction via simply modulating the surface chemistry of nanocrystals. Our present sensing system for vitamin C exhibits a rapid response rate of less than 2 min, and highly selective and ultrasensitive detection with a detection limit of 108 nM, which is two orders of magnitude lower than that acquired by previously reported methods. The repeated reversibility of fluorescence quenching/recovery with time revealed a high reproducibility and long-term stability of our sensing materials. Furthermore, our developed sensing material overcomes the disadvantages such as complex surface modification/immobilization and serious biotoxicity compared to quantum-dot-based fluorescent sensing systems.

Energy transfer study between Ce3+ and Tb3+ ions in doped and core-shell sodium yttrium fluoride nanocrystals

Here, we report the preparation of Ce(3+) and Tb(3+) co-doped sodium yttrium fluoride nanorods and NaYF(4):Ce(3+)/Tb(3+) core-shell nanoparticles by the emulsion method. The core-shell nanoparticles are confirmed by X-ray diffraction study and transmission electron microscopy (TEM) analysis. The hexagonal crystal phase of Ce(3+)-doped sodium yttrium fluoride nanocrystals is converted to the cubic polymorph after surface coating by TbF(3). Cell volume, cell parameters and lattice strain have been modified due to core-shell structure. The decay times are found to be 8.4 ms and 5.4 ms for doped nanorods and core-shell nanoparticles, respectively, which reveals that non-radiative decay is higher in the case of core-shell nanoparticles than doped nanorods. Energy transfer efficiencies from Ce(3+) to Tb(3+)are 65% and 45% for doped Na(Y(1.5)Na (0.5))F(6):Ce:Tb material and NaYF(4):Ce/Tb core-shell materials, respectively. Quantum yields are found to be 75% and 42% for doped and core-shell samples, respectively.

Enhanced Performance in Vapor O-Methylation of Hydroxybenzene Over a Noval Kind of Mesoporous Rare Earth Phosphate

Mesoporous rare earth phosphates (MREPs) have been prepared by template method. The mesoporous structure of these materials has been characterized by XRD and TEM measurement. The catalytic performance of these materials in vapor O-methylation of hydroxybenzene has been investigated. These MREPs show higher performance in O-methylation of hydroxybenzene than the materials prepared without template. The excellent performance of these MREPs could be ascribed to their porous structure and much more amount of active sites.

Facile ligand-exchange with polyvinylpyrrolidone and subsequent silica coating of hydrophobic upconverting beta-NaYF(4):Yb(3+)/Er(3+) nanoparticles

A facile ligand-exchange strategy with a water-soluble polymer, i.e. polyvinylpyrrolidone (PVP), to replace the surface passivating oleate ligands on the beta-NaYF(4) nanoparticle surface is reported. Highly monodisperse oleate-stabilized beta-NaYF(4) nanoparticles were synthesized and the oleates were exchanged with a commercially available PVP allowing the phase transfer of these nanoparticles. The exchanged nanoparticles are readily dispersible in water and other polar solvents. To show the effectiveness of the exchange reaction we used the affinity of the PVP chains to silica and coated the nanoparticles with a uniform, thin silica shell. The PVP exchanged and silica-coated nanoparticles show longer colloidal stability and no surfactant related problems as compared to the reverse microemulsion-based silica-coated nanoparticles, which show a high tendency to aggregate, when removed from the microemulsion. The optical properties of the ligand-exchanged nanoparticles dispersed in water were compared with that of the oleate-stabilized nanoparticles in organic solvents. A decrease in the upconversion emission intensity and a different relative ratio of the green and red upconverted light were observed for the particles dispersed in water after ligand-exchange. PVP is a highly biocompatible polymer and is reported to have a longer blood circulation time and very low accumulation in vital organs, two highly desired properties for in vivo studies. This ligand-exchange strategy opens a new pathway to study the use of beta-NaYF(4) for biological applications in vivo.

Surface modification, functionalization and bioconjugation of colloidal inorganic nanoparticles

Inorganic colloidal nanoparticles are very small, nanoscale objects with inorganic cores that are dispersed in a solvent. Depending on the material they consist of, nanoparticles can possess a number of different properties such as high electron density and strong optical absorption (e.g. metal particles, in particular Au), photoluminescence in the form of fluorescence (semiconductor quantum dots, e.g. CdSe or CdTe) or phosphorescence (doped oxide materials, e.g. Y(2)O(3)), or magnetic moment (e.g. iron oxide or cobalt nanoparticles). Prerequisite for every possible application is the proper surface functionalization of such nanoparticles, which determines their interaction with the environment. These interactions ultimately affect the colloidal stability of the particles, and may yield to a controlled assembly or to the delivery of nanoparticles to a target, e.g. by appropriate functional molecules on the particle surface. This work aims to review different strategies of surface modification and functionalization of inorganic colloidal nanoparticles with a special focus on the material systems gold and semiconductor nanoparticles, such as CdSe/ZnS. However, the discussed strategies are often of general nature and apply in the same way to nanoparticles of other materials.

Synthesis and luminescence of CePO4:Tb/LaPO4 core/sheath nanowires

CePO(4):Tb/LaPO(4) nanowires with a core/sheath architecture have been successful synthesized by a facile aqueous chemical method mediated by original CePO(4):Tb aggregation seeds. The seed crystals serve as both a luminescence center and a nucleation site for epitaxial growth. The seed nanocrystals have an irregular sphere-like shape with an average size of around 6.8 nm and a narrow size distribution. When the seed crystals are coated with LaPO(4), the resulting core/sheath CePO(4):Tb/LaPO(4) nanowires have mean diameters of about 7.6 nm and lengths up to 331 nm. Both photo- and x-ray luminescence demonstrate that the LaPO(4) coating increases the luminescence efficiency. These core/sheath structured nanowires may find potential applications in solid state lighting, medical imaging and radiation detection.

Ambient large-scale template-mediated synthesis of high-aspect ratio single-crystalline, chemically doped rare-earth phosphate nanowires for bioimaging

A simple and effective template-mediated protocol has been developed for the large-scale, room-temperature preparation of high-aspect-ratio, single-crystalline Tb-doped CePO(4) nanowires, measuring approximately 12 nm in diameter and over 10 mum in length. Moreover, we also isolated sheaf-like bundles of nanostructures. The synthesis mechanism likely involved a crystal splitting step. The resulting nanowires demonstrated an intense redox-sensitive green photoluminescence, which was exploited, in addition to their inherently high biocompatibility and low toxicity, for potential applications in biological imaging and labeling of cells.

One-step synthesis of folic acid protected gold nanoparticles and their receptor-mediated intracellular uptake

We report here a facile method to obtain folic acid (FA)-protected gold nanoparticles (Au NPs) by heating an aqueous solution of HAuCl(4)/FA in which FA acts as both the reducing and stabilizing agent. The successful formation of FA-protected Au NPs is demonstrated by UV/Vis spectroscopy, transmission electron microscopy (TEM), selected-area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The intracellular uptake of these nanoparticles is facilitated by HeLa cells overexpressing the folate reporter, which itself is significantly inhibited by free FA in a competitive assay as quantified by inductively coupled plasma mass spectroscopy (ICP-MS). This simple one-step approach affords a new perspective for creating functional nanomaterials, and the resulting biocompatible, functional Au NPs may find some prospective applications in various biomedical fields.

Functionalized Mesoporous SBA-15 with CeF3: Eu3+ Nanoparticle by Three Different Methods: Synthesis, Characterization, and Photoluminescence

Luminescence functionalization of the ordered mesoporous SBA-15 silica is realized by depositing a CeF3: Eu3+ phosphor layer on its surface (denoted as CeF3: Eu3+/SBA-15/IS, CeF3: Eu3+/SBA-15/SI and CeF3: Eu3+/SBA-15/SS) using three different methods, which are reaction in situ (I-S), solution impregnation (S-I) and solid phase grinding synthesis (S-S), respectively. The structure, morphology, porosity, and optical properties of the materials are well characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, N2 adsorption, and photoluminescence spectra. These materials all have high surface area, uniformity in the mesostructure and crystallinity. As expected, the pore volume, surface area, and pore size of SBA-15 decrease in sequence after deposition of the CeF3: Eu3+ nanophosphors. Furthermore, the efficient energy transfer in mesoporous material mainly occurs between the Ce3+ and the central Eu3+ ion. They show the characteristic emission of Ce3+ 5d → 4f (200-320 nm) and Eu3+5D0 → 7FJ(J = 1-4, with 5D0 → 7F1 orange emission at 588 nm as the strongest one) transitions, respectively. In addition, for comparison, the mesoporous material CeF3: Eu3+/SBA-15/SS exhibits the characteristic emission of Eu3+ ion under UV irradiation with higher luminescence intensity than the other materials.

Multimodal-luminescence core-shell nanocomposites for targeted imaging of tumor cells

Uniform silica-coated NaYF(4): 20 mol % Yb, 2 mol % Er nanocomposites with good dispersibility, containing organic dye incorporated in the silica shell and folic acid conjugated on the surface of the shell, were prepared and characterized. The core-shell nanocomposites are 20-22 nm in size, water soluble, and buffer stable, with good photostability and biocompatibility. Folic acid (FA) offers a means of targeting human cells that greatly overexpress the folate receptor (FR). By the use of confocal microscopy and quantitative flow cytometry analysis, we demonstrate the receptor-mediated delivery of FA-conjugated nanocomposites targeting FR-positive cell lines, such as KB cells. The receptor-mediated targeting was confirmed by a comparison with the uptake of these nanocomposites in FR-negative cell lines, such as MCF-7. These results show that the silica-coated upconverting nanophosphor (UCNP) nanocomposites prepared by our strategy can potentially be useful as multimodal bioimaging agents.

Chloroform- and water-soluble sol-gel derived Eu+++/Y2O3 (red) and Tb+++/Y2O3 (green) nanophosphors: synthesis, characterization, and surface modification

Eu+++ and Tb+++ ions have been incorporated into nanodimensional yttrium oxide host matrices via a sol-gel process using Y5O(OPr(i))13 as precursor (OPr(i) = isopropoxy). The as-synthesized white powders have been annealed at different temperatures. Photoluminescence (PL) spectroscopy and X-ray diffraction (XRD) have been used as tools for documenting the characteristics of these powders. For Eu+++-doped powders, a comparison of the Eu+++, 5D0-->7F1, and 5D0-->7F2 peak intensities in the emission spectra reveals that the dopant ions are occupying unsymmetrical sites in the host yttrium oxide in all the samples. For Tb+++-doped powders, the characteristic terbium 5D3-->7Fn and 5D-->7Fn (n = 2-6) transitions were visible only in the samples that had been annealed above 500 degrees C. Samples of the doped particle powders were suspended in chloroform by fragmenting the powder with and without sonification under the presence of trioctylphosphine oxide, or a mixture of oleic acid and dioctyl ether. The resulting clear colorless (for Eu+++) and light green translucent (for Tb+++) solutions of the suspended particles showed red and green luminescence upon UV excitation, respectively. In addition, suspension in water has been achieved by fragmenting the powder in the presence of dichloroacetic acid. Transmission electron micrograph investigation of the soluble particles shows single dispersed particles along with agglomerates. The changes in the luminescence due to fragmentation of the particle powder and due the influence of the surfactant of the suspended colloidal particles are discussed.

Synthesis and bio-functionalization of multifunctional magnetic Fe(3)O(4)@Y(2)O(3):Eu nanocomposites

A facile homogenous precipitation method has been developed for the synthesis of multifunctional, magnetic, luminescent nanocomposites with Fe(3)O(4) nanoparticles as the core and europium-doped yttrium oxide (Y(2)O(3):Eu) as the shell. The nanocomposites showed both super-paramagnetic behavior and unique europium fluorescence properties with high emission intensity. Their surface has been modified with a bifunctional ligand, p-aminobenzoic acid (PABA), and further biofunctionalized with biotin; the nanocomposites showed specific targeting for avidin-coupled polystyrene beads.

Organic functionalization of luminescent oxide nanoparticles toward their application as biological probes

Luminescent inorganic nanoparticles are now widely studied for their applications as biological probes for in vitro or in vivo experiments. The functionalization of the particles is a key step toward these applications, since it determines the control of the coupling between the particles and the biological species of interest. This paper is devoted to the case of rare earth doped oxide nanoparticles and their functionalization through their surface encapsulation with a functional polysiloxane shell. The first step of the process is the adsorption of silicate ions that will act as a primary layer for the further surface polymerization of the silane, either aminopropyltriethoxysilane (APTES) or glycidoxypropyltrimethoxysilane (GPTMS). The amino- or epoxy- functions born by the silane allow the versatile coupling of the particles with bio-organic species following the chemistry that is commonly used in biochips. Special attention is paid to the careful characterization of each step of the functionalization process, especially concerning the average number of organic functions that are available for the final coupling of the particles with proteins. The surface density of amino or epoxy functions was found to be 0.4 and 1.9 functions per square nanometer for GPTMS and APTES silanized particles, respectively. An example of application of the amino-functionalized particles is given for the coupling with alpha-bungarotoxins. The average number (up to 8) and the distribution of the number of proteins per particle are given, showing the potentialities of the functionalization process for the labeling of biological species.

Luminescent rare earth nanomaterials for bioprobe applications

Inorganic fluorescent nanoparticles (NPs) have initiated an extensive upsurge in biological application research. Just as quantum dots are regarded as a vigorous reinforcement of the organic dye family, rare earth (RE) fluorescent NPs, as another phosphors branch, also possess unique optical characteristics. The advantages of RE NPs in photostability and colorimetric purity make them suitable for bioprobe applications. Since the preparation technologies have been well developed, it is favourable to prompt the research in the interdisciplinary field of biology and material sciences. Herein, we summarize the synthesis and performance, together with bioprobe applications of RE oxide, sulfoxide, vanadate, phosphate, fluoride, and sodium RE fluoride nanomaterials. The prospects of these promising materials as applied in the biological field is described to draw readers' attention and to attract more research interest.

Fabrication of novel luminor Y(2)O(3):Eu(3+)@SiO(2)@YVO(4):Eu(3+) with core/shell heteronanostructure

A novel polychromic phosphor with core-shell heteronanostructure has been prepared to improve the chromatic index of phosphors. As for the first example, Y(2)O(3):Eu(3+)@SiO(2)@YVO(4):Eu(3+), its synthetic route, structure and optical properties are presented in this paper. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), energy-dispersive x-ray spectra (EDS) and photoluminescence (PL) were all employed to characterize the composite core-shell phosphors. The XRD, FE-SEM and HR-TEM results indicate that the SiO(2) and YVO(4):Eu(3+) layers have been successfully coated on Y(2)O(3):Eu(3+) nanoparticles and SiO(2) layer, respectively: these layers were further verified by the EDS. The PL showed that the red-emitting phosphor Y(2)O(3):Eu(3+)@SiO(2)@YVO(4):Eu(3+) possessed the independent luminescent properties of both the core Y(2)O(3):Eu(3+) and the shell YVO(4):Eu(3+). The emissions were dominated by [Formula: see text] or [Formula: see text] transitions of Eu(3+) when excited with different wavelengths. Since this broad-band response to excitation in the range of 225-340 nm gave more red/dark red emissions found at 612, 616 and 620 nm, the novel phosphor Y(2)O(3):Eu(3+)@SiO(2)@YVO(4):Eu(3+) could have potential biological labeling applications with wide flexibility.