Tandem dye acceptor used to enhance upconversion fluorescence resonance energy transfer in homogeneous assays

In fluorescence resonance energy transfer (FRET)-based assays, spectral separation of acceptor emission from donor emission is a common problem affecting the assay sensitivity. The challenge derives from small Stokes shifts characteristic to conventional fluorescent dyes resulting in leakage of donor emission to the measurement window intended only to collect the acceptor emission. We have studied a FRET-based homogeneous bioaffinity assay utilizing a tandem dye acceptor with a large pseudo-Stokes shift (139 nm). The tandem dye was constructed using B-phycoerythrin as an absorber and multiple Alexa Fluor 680 dyes as emitters. As a donor, we employed upconverting phosphor particles, which uniquely emit at visible wavelengths under low-energy infrared excitation enabling the fluorescence measurements free from autofluorescence even without time-resolved detection. With the tandem dye, it was possible to achieve four times higher signal from a single binding event compared to the conventional Alexa Fluor 680 dye alone. Tandem dyes are widely used in cytometry and other multiplex purposes, but their applications can be expanded to fluorescence-based homogeneous assays. Both the optimal excitation and emission wavelengths of tandem dye can be tuned to a desired region by choosing appropriate fluorophores enabling specifically designed acceptor dyes with large Stokes shift.     

Upconversion fluorescence resonance energy transfer in a homogeneous immunoassay for estradiol

We recently described a novel homogeneous assay principle based on upconversion fluorescence resonance energy transfer (UC-FRET), where an upconverting phosphor (UCP) is utilized as a donor. The UC-FRET has now been applied to a competitive homogeneous immunoassay for 17beta-estradiol (E2) in serum, using a small-molecular dye as an acceptor. The assay was constructed by employing an UCP coated with an E2-specific recombinant antibody Fab fragment as a donor and an E2-conjugated small-molecular dye, Oyster-556, as an acceptor. Standard curves for the assay were produced both in buffer and in male serum. Sensitized acceptor emission was measured at 600 nm under continuous laser diode excitation at 980 nm. In buffer, the IC50 value of the assay was 1 nM and in serum 3 nM. The lower limits of detection (mean of zero calibrators, 3 SD) were 0.4 and 0.9 nM, respectively. The measurable concentration range extended up to 3 nM in buffer and 9 nM in serum. Equilibrium in the assay was reached in 30 min. The novel principle of UC-FRET has unique advantages compared to present homogeneous luminescence-based methods and can enable an attractive assay system platform for clinical diagnostics and for high-throughput screening approaches.     

白光LED用红色荧光粉MMoO4:Eu3+（M=Ca,Sr,Ba）的制备与表征

采用高温固相法制备了红色荧光粉MMoO4:Eu3+(M=Ca,Sr,Ba),用XRD和荧光分光光度计对其物相及发光性能进行表征和研究。结果表明,在800℃时可得到MMoO4(M=Ca,Sr,Ba)物相结构。分别以395nm的近紫外光和465nm的可见光激发样品,MMoO4:Eu3+(M=Ca,Sr,Ba)荧光粉发红光,对应于Eu3+的4f-4f跃迁,其中以616nm发光最强。荧光粉在395nm和465nm的吸收分别与紫外光和蓝光LED芯片相匹配。     

Oligonucleotide array-in-well platform for detection and genotyping human adenoviruses by utilizing upconverting phosphor label technology

We have developed a robust array-in-well test platform based on an oligonucleotide array, combining advantages of simple instrumentation and new upconverting phosphor reporter technology. Upconverting inorganic lanthanide phosphors have a unique property of photoluminescence emission at visible wavelengths under near-infrared excitation. No autofluorescence is produced from the sample or support material, enabling a highly sensitive assay. In this study, the assay is performed in standard 96-well microtiter plates, making the technique easily adaptable to high-throughput analysis. The oligonucleotide array-in-well assay is employed to detect a selection of ten common adenovirus genotypes causing human infections. The study provides a demonstration of the advantages and potential of the upconverting phosphor-based reporter technology in multianalyte assays and anti-Stokes photoluminescence detection with an anti-Stokes photoluminescence imaging device.     

Development of a time-resolved fluorometric detection system using diffusion-enhanced energy transfer

A novel detection system using both emission energy transfer and time-resolved fluorometry (TRF) was developed, with a europium chelate as the energy donor and a novel fluorophore SNR1, excitable with long-wavelength light corresponding to europium emission, as the energy acceptor. When the donor and acceptor molecules were mixed in solution, energy transfer was observed without direct attachment of the donor and the acceptor, via a diffusion-enhanced energy-transfer mechanism. Thus, the acceptor emission can be detected as a long-lifetime fluorescence in TRF. When the fluorescence properties of the acceptor molecule are changed by interaction with an enzyme or other bioactive molecule, the change can be detected as a long-lived sensitized emission. If we develop or select suitable acceptor molecules, this simple and convenient system should be applicable to a wide variety of bioactive molecules. Since it is based on TRF, it can be used for high-resolution assay.     

Infrared up-converting phosphors for bioassays

The development of up-converting phosphor reporter particles has added a powerful tool to modern detection technologies. Carefully constructed phosphor reporters have core-shell structures with surface functional groups suitable for standard bio-conjugations. These reporters are chemically stable, possess the unique property of infrared up-conversion, and are readily detected. In contrast to conventional fluorescent reporters, up-converting phosphor particles do not bleach and allow permanent excitation with simultaneous signal integration. A large anti-Stokes shift (up to 500 nm) separates discrete emission peaks from the infrared excitation source. Along with the unmatched contrast in biological specimens due to the absence of autofluorescence upon infrared excitation, up-converting phosphor technology (UPT) has unique properties for highly-sensitive particle-based assays. The production and characteristics of UPT reporter particles as well as their application in various bioassays is reviewed.     

Fabrication of nano-sized emitting phosphors for photoluminescence films via hydro-thermal synthesis

Nano-sized red and blue emitting phosphors for a photoluminescence film were fabricated via hydrothermal synthesis through the sol-gel process. The nano-sized phosphors had a spherical shape such as the 60-110 nm Y2O2S:Eu3+ phosphor and the 45-90 nm of Y2SiO5:Ce phosphor. Firing at 1000 degrees C for 2 hours resulted in an increase in their size to 90-190 nm for the Y2O2S:Eu3+ phosphor and 70-160 nm for the Y2SiO5:Ce phosphor. Heat treatment of the gel powders of the emitting phosphors above 730 degrees C was recommended because of their crystallization. The maximum excitation and emission intensities of the red and blue phosphors with Y2O2S:Eu3+ and Y2SiO5:Ce were at the wavelengths of 308 nm and 617 nm, and 254 nm and 464 nm, respectively. The photoluminescence of the films increased as increasing the content of the red and blue phosphor powder mixture in the plastic films. The 100 microm-thick PVB film with the nano-sized phosphors showed the maximum photoluminescence of 537 x 1000 counts/sec.     

溶胶-凝胶法和微波辐射法制备Mg2SiO4Mn2＋红色荧光粉制备及发光性质的研究

采用溶胶-凝胶法和微波辐射法制备了Mg2SiO4Mn2＋红色发光材料。研究了以Mg2SiO4为基质,在掺杂Mn2＋的情况下,微波合成时间和Mn2＋的掺杂浓度对发光性能的影响。选择最佳微波合成时间和Mn2＋的掺杂浓度,制备了在410nm激发下,发光中心位于690nm的红色发光材料。     

A novel blue-emitting NaSrPO4:Eu phosphor for near UV based white light-emitting-diodes

A novel blue-emitting phosphor based on a phosphate host matrix, NaSrPO₄:Eu²⁺, was prepared by a conventional solid-state reaction method. The NaSrPO₄:Eu²⁺ phosphor was efficiently excited at wavelengths of 250-450 nm, which is suitable for the emission band of near ultraviolet (n-UV) light-emitting-diode (LED) chips (350-430 nm). The NaSrPO₄:Eu²⁺ phosphor exhibits a strong blue emission peaking at 453 nm and broadly weak green and red emission bands up to 700 nm. The effect of the activated Eu²⁺ concentration on the emission intensity of the NaSrPO₄:Eu²⁺ was also investigated. Here, a phosphor-converted LED (pc-LED) was fabricated and exhibits bright blue emission under a forward bias of 20 mA. All of these characteristics suggest that the NaSrPO₄:Eu²⁺ phosphors could be applicable to n-UV based white LEDs.     

Combustion synthesis of Eu2?+? and Dy3?+? activated Sr3(VO4)2 phosphor for LEDs

Combustion synthesis and photoluminescence (PL) characterization of Sr₃(VO₄)₂:Eu,Dy phosphors are presented in this paper. PL emission of Sr₃(VO₄)₂:Eu phosphor shows green broad emission band centring at 511 nm and a red sharp band at 614 nm by excitation wavelength of 342 nm. The PL emission spectrum of Sr₃(VO₄)₂:Dy phosphor exhibits an intense blue emission peak at 479 nm, yellow broad band centring at 573 nm and red band at 644 nm by the excitation wavelength of 426 nm in near visible blue region. The excitation wavelength of Eu (342 nm) and Dy (426 nm) activated Sr₃(VO₄)₂ phosphor are well matched with the excitation of near UV excited solid state lighting and blue chip excitation of light emitting diodes, respectively. The effect of Eu^2 +and Eu^3 +ions concentration on the emission intensity of Sr₃(VO₄)₂ was also investigated. The Sr₃(VO₄)₂:Eu is a potential green and red emitting phosphor as well as Sr₃(VO₄)₂:Dy is blue and yellow emitting phosphor for solid state lighting i.e. white LEDs. The XRD and SEM characteristics of Sr₃(VO₄)₂ materials was also reported in this paper.     

Ce、Cr∶YAG微晶玻璃的制备及光谱性能研究

目前白光LED在红光波段发射较弱,导致其显色指数偏低,在白光LED用Ce∶YAG微晶玻璃中掺入Cr3+来增强红光波段的发射,从而提高显色指数。通过X射线衍射、荧光光度计、电光源参数测试对样品的晶相、光谱性能及荧光寿命进行了表征。研究了Cr3+对Ce∶YAG微晶玻璃发光性能的影响,并对其增红机理进行了初步的探讨。结果表明基质玻璃在1400℃热处理可析出纯的YAG晶相;Ce∶YAG和Ce、Cr∶YAG微晶玻璃在460nm激发下,在480～650nm产生有效发射,发射光谱中心波长位于530nm;由于Ce3+(2E)-Cr3+(4T)之间的非辐射能量传递,Ce、Cr∶YAG微晶玻璃在688、692和705nm处有红色发射峰,能有效地提高白光LED的显色性能。     

Deep Red Emissive Carbonized Polymer Dots with Unprecedented Narrow Full Width at Half Maximum

Development of high-performance carbon dots (CDs) with emission wavelength longer than 660 nm (deep red emission) is critical in deep-tissue bioimaging, yet it is still a major challenge to obtain CDs with both narrow full width at half maximum (FWHM) and high deep red/near-infrared emission yield. Here, deep red emissive carbonized polymer dots (CPDs) with unprecedented FWHM of 20 nm are synthesized. The purified CPDs in dimethyl sulfoxide (DMSO) solution possess quantum yield (QY) as high as 59% under 413 nm excitation, as well as recorded QY of 31% under 660 nm excitation in the deep red fluorescent window. Detailed characterizations identify that CPDs have unique polymer characteristics, consisting of carbon cores and the shells of polymer chains, and π conjugated system formed with N heterocycles and aromatic rings governs the single photoluminescence (PL) center, which is responsible for high QY in deep red emissive CPDs with narrow FWHM. The CPDs exhibit strong absorption and emission in the deep red light region, low toxicity, and good biocompatibility, making them an efficient probe for both one-photon and two-photon bioimaging. CPDs are rapidly excreted via the kidney system and hepatobiliary system.     

Red and green fluorescence of Mn in NaCl

The fluorescence (emission and excitation) spectrum of Mn²⁺ ion in NaCl has been investigated for freshly quenched samples (diluted Mn²⁺ ions) and as grown samples (Mn²⁺ ions forming aggregates and/or precipitates). Two main emission bands are generally observed in as grown samples, peaking at 505 nm and around 610 nm. Both emission bands are related to different manganese precipitates. Quenched samples show only the red emission but peaking at 605 nm and with a different excitation spectrum to that of the as grown crystals. Thus, this crystal is suitable to operate as a double color (red and green) emitting phosphor where the red and green relative intensities can be controlled by a thermal treatment.     

Template-free Fabrication and Luminescent Characterization of Highly Uniform and Monodisperse Y2O2S:Sm3+ Hollow Submicrospheres

Well dispersed and homogeneous Y2O2S:Sm3+ hollow submicrospheres were successfully achieved by a templatefree solvothermal method combining with a postcalcining process.The crystalstructure and particle morphology were investigated by the X-ray diffraction(XRD),Fourier transform infrared(FT-IR) spectra,scanning and transmission electron microscopy(SEM and TEM),respectively.A possible growth mechanism was proposed to reveal the formation process.Luminescence properties of the Y2O2S:Sm3+ long-lasting phosphor were analyzed by measuring the excitation spectra,emission spectra,afterglow decay curve and thermoluminescence curve.The excitation spectra indicated that the phosphor could be excited effectively by the ultraviolet-light emitting diode(UV-LED) or blue LED,and the emission spectra showed that the phosphor could emit red light from 600 to 650 nm.     

Preparation, characterization and luminescence of a new green-emitting phosphor: Gd2TeO6 doped with Tb

Novel green-emitting Gd_2 − xTb_xTeO₆ powder phosphor has been prepared by the oxidation of corresponding rare-earth oxytellurides. The photoluminescence (PL) properties were reported. Five dominant bands centered at 302 nm, 318 nm, 339 nm, 353 nm and 378 nm characterize the excitation spectrum. Under the excitation of 378 nm UV light, the emission spectrum exhibits an intense peak centered at 543-548 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺. This phosphor can be excited by light with wavelengths of 350-400 nm and therefore can be used as a green phosphor for white lighting devices utilizing near-UV LED as a light source.     

The sol-gel process synthesis of GdAl3(BO3)4:Eu3+ nanophosphors

GdAl3(BO3)4:Eu3+ red phosphors were prepared using citric acid as complex agent by sol-gel technique. The preparation conditions of the precursor synthesis, including crystallization temperature and crystallization time were investigated. Their structure and luminescence properties were characterized by X-ray diffraction (XRD) analysis and fluorescence spectrometry. The results showed that GdAl3(BO3)4:Eu3+ phosphor crystallized at 960 degrees C for 2 h have been synthesized by sol-gel method. The phosphor is distributed into hexagonal system and the lattice parameters are a = 9.2992 nm c = 7.2577 nm. The excitation spectrum of Gd(0.95)Al3(BO3)4:Eu(0.05)3+ samples is complex and the frequency scale is wide. It consists of a number of main excitation transitions namely 8S(7/2) --> 6IJ (270 nm) of Gd3+, and the others 7F0 --> 5L6 (400 nm), 7F0 --> 5D2 (472 nm) and 7F0 --> 5D1 (542 nm) of Eu3+. The main emission peaks are 614 nm and 619 nm, which are the characteristic emission peaks of Eu3+. These emission peaks correspond to the transition from 5D0 to 7F2 of Eu3+. The shape and the wavelength range of the emission spectrum are similar when the sample was excited by different excitation spectrum. Only the relative intensity of the emission peaks is different from each other.     

Cl~-,S~(2-)共掺杂氧化锌荧光粉的制备及发光性能

在空气气氛中,以NH_4Cl为助剂,通过热氧化硫化锌,制备出Cl~-,S~(2-)共掺杂氧化锌荧光粉,激发和发射光谱随氧化温度的变化而变化.在350nm激发下,氧化锌荧光粉的发射光谱只有510nm绿色峰,并有黄色区拖尾现象.绿色峰强度随煅烧温度的变化而变化.绿色峰归因与一价氧空位中的电子和价带中光生空穴的复合.氧化锌荧光粉的光致发光谱的变化是Cl~-,S~(2-)共掺杂的结果.     

Luminescent properties of Eu3+ activated MLa2(MoO4)4 based (M = Ba,Sr and Ca) novel red-emitting phosphors

Eu³⁺-activated novel red phosphors, MLa₂(MoO₄)₄ (M = Ba, Sr and Ca) were synthesized by the conventional solid state method. The excitation and emission spectra indicate that these phosphors can be effectively excited by UV (395 nm) and blue (466 nm) light, and exhibit a satisfactory red performance at 614 nm. Upon excitation with a 466 nm light, our synthesized phosphors have stronger emission intensity than the sulfide red phosphors used in white LEDs. Due to high emission intensity and a good excitation profile, the Eu³⁺-doped CaLa₂(MoO₄)₄ phosphor may be a promising candidate in solid-state lighting applications.     

Luminescence properties of a red phosphor europium tungsten oxide Eu2WO6

Eu₂WO₆ was synthesized by the conventional solid state reaction method. Crystal phase was characterized by the X-ray powder diffraction. The excitation and emission spectra indicate that this phosphor can be effectively excited by near UV (395 nm) and blue light (465 nm), and the emission spectra exhibit a satisfactory red performance at 611 nm, which is due to the characteristic ⁵D₀?⁷F₂ transitions of Eu³⁺ ions. The luminescence intensities and color purity were investigated by increasing the fired temperature. The phosphor shows stable luminescence and color purity at high temperature.     

N-B-Al共掺荧光4H-SiC施主受主对发光性能研究

施主受主共掺杂的荧光4H-SiC可以通过复合发出可见光, 影响其发光性能的一个重要因素是施主-受主掺杂的浓度。本研究通过PVT生长方法制备了3英寸N-B-Al共掺的4H-SiC晶体, 采用Raman光谱、SIMS对晶体的结晶类型和掺杂浓度进行了表征; 采用PL发射谱和激发谱、荧光衰减曲线表征和内量子效率对晶体的发光波长、强度、施主-受主对复合发光性能进行了研究。结果发现, 低浓度Al掺杂样品在室温下发出黄绿色荧光。低浓度Al掺杂在晶体中提供较少的受主; 高浓度B、N掺杂形成施主, 从而贡献充足的电子-空穴对。这些电子-空穴的复合提高了施主-受主对复合的内量子效率, 进而增强光致发光强度, 增加平均发光寿命。