A Lanthanide‐Complex‐Based Ratiometric Luminescent Probe Specific for Peroxynitrite

A lanthanide‐complex‐based ratiometric luminescence probe specific for peroxynitrite (ONOO^?), 4′‐(2,4‐dimethoxyphenyl)‐2,2′:6′,2′′‐terpyridine‐6,6′′‐diyl]bis(methylenenitrilo)tetrakis(acetate)‐Eu³⁺/Tb³⁺ ([Eu³⁺/Tb³⁺(DTTA)]), has been designed and synthesized. Both [Eu³⁺(DTTA)] and [Tb³⁺(DTTA)] are highly water soluble with large stability constants at ≈10²⁰, and strongly luminescent with luminescence quantum yields of 10.0 and 9.9 %, respectively, and long luminescence lifetimes of 1.38 and 0.26 ms, respectively. It was found that the luminescence of [Tb³⁺(DTTA)] could be quenched by ONOO^? rapidly and specifically in aqueous buffers, while that of [Eu³⁺(DTTA)] did not respond to the addition of ONOO^?. Thus, by simply mixing [Eu³⁺(DTTA)] and [Tb³⁺(DTTA)] in an aqueous buffer, a ratiometric luminescence probe specific for time‐gated luminescence detection of ONOO^? was obtained. The performance of [Tb³⁺(DTTA)] and [Eu³⁺/Tb³⁺(DTTA)] as the probes for luminescence imaging detection of ONOO^? in living cells was investigated. The results demonstrated the efficacy and advantages of the new ratiometric luminescence probe for highly sensitive luminescence bioimaging application.     

Luminescent properties of Tb3+ and Gd3+ ions doped aluminosilicate oxyfluoride glasses

Tb³⁺ and Gd³⁺ ions doped lithium–barium–aluminosilicate oxyfluoride glasses have been prepared. The transmission, emission and excitation spectra were measured. It has been found that those Tb³⁺-doped lithium–barium–aluminosilicate oxyfluoride glasses exhibit good UV-excited luminescence. The luminescence intensity of Tb³⁺ ion increases for those (Tb³⁺, Gd³⁺)-codoped glasses. Energy transfer process from Gd³⁺ ion to Tb³⁺ ion is indicated.     

Development of a ratiometric time-resolved luminescence sensor for pH based on lanthanide complexes

Time-resolved luminescence bioassay technique using lanthanide complexes as luminescent probes/sensors has shown great utilities in clinical diagnostics and biotechnology discoveries. In this work, a novel terpyridine polyacid derivative that can form highly stable complexes with lanthanide ions in aqueous media, (4′-hydroxy-2,2′:6′,2′′-terpyridine-6,6′′-diyl) bis(methylenenitrilo) tetrakis(acetic acid) (HTTA), was designed and synthesized for developing time-resolved luminescence pH sensors based on its Eu³⁺ and Tb³⁺ complexes. The luminescence characterization results reveal that the luminescence intensity of HTTA–Eu³⁺ is strongly dependent on the pH values in weakly acidic to neutral media (pK_a = 5.8, pH 4.8–7.5), while that of HTTA–Tb³⁺ is pH-independent. This unique luminescence response allows the mixture of HTTA–Eu³⁺ and HTTA–Tb³⁺ (the HTTA–Eu³⁺/Tb³⁺ mixture) to be used as a ratiometric luminescence sensor for the time-resolved luminescence detection of pH with the intensity ratio of its Tb³⁺ emission at 540 nm to its Eu³⁺ emission at 610 nm, I_540 nm/I_610 nm, as a signal. Moreover, the UV absorption spectrum changes of the HTTA–Eu³⁺/Tb³⁺ mixture at different pHs (pH 4.0–7.0) also display a ratiometric response to the pH changes with the ratio of absorbance at 290 nm to that at 325 nm, A_290 nm/A_325 nm, as a signal. This feature enables the HTTA–Eu³⁺/Tb³⁺ mixture to have an additional function for the pH detection with the absorption spectrometry technique. For loading the complexes into the living cells, the acetoxymethyl ester of HTTA was synthesized and used for loading HTTA–Eu³⁺ and HTTA–Tb³⁺ into the cultured HeLa cells. The luminescence imaging results demonstrated the practical utility of the new sensor for the time-resolved luminescence cell imaging application.     

Study of the luminescence properties of a novel rare earth complex Tb(DPC)22H2O

Rare earth complex Tb(DPC)₂2H₂O was synthesized by introducing Pyridine-2,6-dicarboxylic acid(H₂DPC) as the ligand and characterized by UV, fluorescent and infrared spectra as well as elemental analysis. The complex exhibited ligand-sensitized green emission, and it has the higher sensitized luminescent efficiency and longer lifetime. The effect and mechanism of the ligand (H₂DPC) on the luminescence properties of terbium complex was discussed. In device ITO/PVK/Tb(DPC)₂2H₂O/Al, Tb³⁺ may be excited by intramolecular energy transfer from ligand as observed by electroluminescence. The main emitting peak at 545 nm can be attributed to the transition of ⁵D₄→⁷F₅ of Tb³⁺ ion and this process results in the enhancement of green emission from electroluminescence device.     

Exceptionally Long‐Lived Luminescence Emitted from TbIII Ion Caged in an AgI–TbIII–Thiacalix[4]arene Supramolecular Complex in Water

The compositions and photophysical properties of luminescent ternary complexes of thiacalix[4]arene‐p‐sulfonate (TCAS), Tb^III, and Ag^I ions were determined. At pH 6, Ag^I₂?Tb^III₂?TCAS₂ formed. Moreover, at pH 10, in the presence of a 20‐fold excess of Ag^I and a 50‐fold excess of TCAS with respect to Tb^III, Ag^I₂?Tb^III?TCAS₂ formed as the main luminescent species. The structure of these complexes was proposed: two TCAS ligands are linked by two S–Ag^I–S linkages to adopt a double‐cone supramolecular structure. Furthermore, each Tb^III ion in the former complex accepts O^?, S, O^? donation, whereas in the latter, the Tb^III center accepts eightfold O^? donation. The luminescence quantum yield (Φ) of Ag^I₂?Tb^III₂?TCAS₂ (0.16) was almost equal to that of Tb^III?TCAS, but the luminescence lifetime τ of the former (=1.09 ms) was larger than that of the latter. For Ag^I₂?Tb^III?TCAS₂, the yield Φ (=0.11) was small, which is attributed to the low efficiency of photosensitization (η=0.11). However, the τ value (4.61 ms) was exceptionally large and almost equal to the natural luminescence lifetime of Tb^III (4.7 ms), which is due to the absence of coordinating water molecules (q=0.1). This is compatible with the proposed structure in which the Tb^III ion is shielded by a supramolecular cage that expels coordinated water molecules responsible for luminescence quenching.     

Spectroscopic studies on the interaction of cilostazole with iodine and 2,3-dichloro-5,6-dicyanobenzoquinone

Lanthanide sensitized luminescence and chemiluminescence (CL) are of great importance because of the unique spectral properties, such as long lifetime, large Stokes shifts, and narrow emission bands characteristic to lanthanide ions (Ln³⁺). With the fluoroquinolone (FQ) compounds including enoxacin (ENX), norfloxacin (NFLX), lomefloxacin (LMFX), fleroxacin (FLRX), ofloxacin (OFLX), rufloxacin (RFX), gatifloxacin (GFLX) and sparfloxacin (SPFX), the luminescence and CL properties of Tb³⁺–FQ and Eu³⁺–FQ complexes have been investigated in this contribution. Ce⁴⁺–SO₃²⁻ in acidic conditions was taken as the CL system and sensitized CL intensities of Tb³⁺–FQ and Eu³⁺–FQ complexes were determined by flow-injection analysis. The luminescence and CL spectra of Tb³⁺–FQ complexes show characteristic peaks of Tb³⁺ at 490 nm, 545 nm, 585 nm and 620 nm. Complexes of Tb³⁺–ENX, Tb³⁺–NFLX, Tb³⁺–LMFX and Tb³⁺–FLRX display relatively strong emission intensity compared with Tb³⁺–OFLX, Tb³⁺–RFX, Tb³⁺–GFLX and Tb³⁺–SPFX. Quite weak peaks with unique characters of Eu³⁺ at 590 nm and 617 nm appear in the luminescence and CL spectra of Eu³⁺–ENX, but no notable sensitized luminescence and CL of Eu³⁺ could be observed when Eu³⁺ is added into other FQ. The distinct differences on emission intensity of Tb³⁺–FQ and Eu³⁺–FQ might originate from the different energy gap between the triplet levels of FQ and the excited levels of the Ln³⁺. The different sensitized luminescence and CL signals among Tb³⁺–FQ complexes could be attributed to different optical properties and substituents of these FQ compounds. The detailed mechanism involved in the luminescence and CL properties of Tb³⁺–FQ and Eu³⁺–FQ complexes has been investigated by analyzing the luminescence and CL spectra, quantum yields, and theoretical calculation results.     

Development of an Organic Dye-Conjugated β-Diketonate-Europium Complex Luminescence Probe for Discrimination and Detection of Intracellular Biothiols

Small molecular biothiols, cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), play important roles in organisms, and their concentration levels are indicative of some human diseases. Herein we report an organic dye-conjugated β-diketonate-Eu³⁺ complex, [Eu(NBD-keto)₃(DPBT)] (NBD-keto: 7-nitro-2,1,3-benzoxadiazole (NBD)-conjugated to 1,1,1,2,2-pentafluoro-5-phenyl-3,5-pentanedionate through a “O” ether bond; DPBT: 2-(N,N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine), which acts as a unique luminescent probe for detecting and discriminating biothiols. [Eu(NBD-keto)₃(DPBT)] itself is not luminescent due to intramolecular interactions between NBD and β-diketonate-Eu³⁺ moieties. Upon reaction with biothiols, the β-diketonate-Eu³⁺ complex [Eu(keto)₃(DPBT)] is generated, which emits long-lived red emission at 610 nm. Meanwhile, three biothiol-substituted NBD derivatives that exhibit different luminescence behaviors, green emissive (short-lived) NBD-NR (R=Cys or Hcy) at 540 nm and non-luminescent NBD-SR (R=GSH), are also generated. These luminescence response behaviors allow time-gated and steady-state luminescence modes to be combined for detecting total biothiols and discriminating GSH and Cys/Hcy. Using this probe, the quantitative detection and discrimination of GSH and Cys/Hcy in lysis solutions of HeLa cells were realized, which revealed the potential of the probe for biomedical applications.     

Hybrid materials of MCM-41 functionalized by lanthanide (Tb, Eu) complexes of modified meta-methylbenzoic acid: Covalently bonded assembly and photoluminescence

Novel organic-inorganic mesoporous hybrid materials were synthesized by linking lanthanide (Tb³⁺, Eu³⁺) complexes to the mesoporous MCM-41 through the modified meta-methylbenzoic acid (MMBA-Si) using co-condensation method in the presence of the cetyltrimethylammonium bromide (CTAB) surfactant as template. The luminescence properties of these resulting materials (denoted as Ln-MMBA-MCM-41, Ln=Tb, Eu) were characterized in detail, and the results reveal that luminescent mesoporous materials have high surface area, uniformity in the ordered mesoporous structure. Moreover, the mesoporous material covalently bonded Tb³⁺ complex (Tb-MMBA-MCM-41) exhibits the stronger characteristic emission of Tb³⁺ and longer lifetime than Eu-MMBA-MCM-41 due to the triplet state energy of organic legend MMBA-Si matches with the emissive energy level of Tb³⁺ very well.     

Effects of gamma radiation on the photoluminescence properties of polycarbonate matrices doped with terbium complex

Luminescent films containing terbium complex [Tb(acac)₃(H₂O)₃] (acac=acetylacetonate) doped into a polycarbonate (PC) matrix were prepared and irradiated at low-dose gamma radiation with ratio of 5 and 10 kGy. The PC polymer was doped with 5% (w/w) of the Tb³⁺ complex. The thermal behavior was investigated by utilization of differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). Changes in thermal stability due to the addition of doping agent into the polycarbonate matrix. Based on the emission spectra of PC:5% Tb(acac)₃ film were observed the characteristic bands arising from the ⁵D₄→⁷F_J transitions of Tb³⁺ ion (J=0–6), indicating the ability to obtain the luminescent films. Doped samples irradiated at low dose of gamma irradiation showed a decrease in luminescence intensity with increasing of the dose.     

Development of a novel terbium(III) chelate-based luminescent probe for highly sensitive time-resolved luminescence detection of hydroxyl radical

Time-resolved (or time-gated) luminescence detection technique using lanthanide chelates as luminescent probes is a widely used and highly sensitive method for the biological applications. The developments of various functional lanthanide probes that can selectively recognize the biological targets are the essential objective of the technique. In this work, a unique Tb³⁺ chelate-based luminescent probe, N,N,N¹,N¹-[2,6-bis(3′-aminomethyl-1′-pyrazolyl)-4-(p-aminophenoxy)methylene-pyridine] tetrakis(acetate)-Tb³⁺(BMPTA-Tb³⁺), has been designed and synthesized for highly selective and sensitive time-resolved luminescence detection of one highly reactive oxygen species (ROS), hydroxyl radical (OH). The probe is almost non-luminescent, and can selectively react with hydroxyl radical to afford a highly luminescent Tb³⁺ chelate, N,N,N¹,N¹-[2,6-bis(3′-aminomethyl-1′-pyrazolyl)-4-hydroxymethyl-pyridine] tetrakis(acetate)-Tb³⁺ (BHTA-Tb³⁺), accompanied by a 49-fold increase in luminescence quantum yield with a long luminescence lifetime (2.76 ms). The luminescence response of the probe to hydroxyl radical is highly selective and insensitive to pH in the physiological pH range. For loading the probe into the living cells, the acetoxymethyl ester of BMPTA-Tb³⁺ was synthesized and used for the HeLa cell loading. Based on this probe, a background-free time-resolved luminescence imaging method for detecting hydroxyl radical in living cells was successfully established.     

Terbium luminescence studies of binding of adriamycin and cisplatin to tumorigenic cells

The luminescent properties of terbium ions are used to investigate the interaction of adriamycin and cisplatin with GH3/B6 pituitary tumor cells. Clinically relevant concentrations of adriamycin were found to quench the intensity (IC₅₀ = 0.6 μM) and excited-state lifetime (τ/τ₀ = 0.73) of the Tb³⁺—GH3/B6 complex. Inspection of the Tb³⁺—GH3/B6 emission spectrum and the visible absorption spectrum of adriamycin strongly strongly suggests that the quenching of Tb³⁺ luminescence by adriamycin is due to dipole-dipole resonant energy transfer; and, according to Forster's theory (R₀ = 33.6 Å), the adriamycin receptor site is located ca. 40 Å away from the bound probe, at the lipid/protein interface. The quenching of Tb³⁺ luminescence by cisplatin is best explained by a static energy-exchange mechanism; in that the cisplatin receptor site is contiguous with the Tb³⁺ binding site at the outer surface of the membrane. The data suggest that, in the plasma membrane of tumorigenic cells, the adriamycin and ciplatin receptor sites are intimately associated with the same calcium-binding protein.     

A Golgi Apparatus-Targetable Probe Based on Lanthanide Complexes for Ratiometric Time-Gated Luminescence Detection of Hydrogen Sulfide

Development of bioanalytical methods for selective and accurate detection of H₂S in living samples is essential for understanding the pathological and physiological functions of this gasotransmitter in biological systems. Here we report a Golgi apparatus-targetable lanthanide complex-based luminescent probe, Golgi-ABTTA-Eu³⁺/Tb³⁺, that can be used for accurately determining H₂S in aqueous solution and living cells via the ratiometric time-gated luminescence (RM-TGL) technique. This probe is composed of 2,2′:6′,2′′-terpyridine-Eu³⁺/Tb³⁺ mixed complexes as the luminophore, 4-azidobenzyl-ether as the responsive moiety, and sulfanilamide as the Golgi apparatus-targeting moiety. Upon reaction with H₂S, accompanied by the cleavage of 4-azidobenzyl group from the probe molecule, the long-lived emission of Tb³⁺ complex at 540 nm is significantly enhanced, while that of Eu³⁺ complex at 610 nm is obviously reduced. It was noted that the I₅₄₀/I₆₁₀ ratio increased by 8.8 times after the probe was exposed to H₂S, which enabled H₂S to be detected with RM-TGL method. After being incubated with living cells, the probe molecules were selectively accumulated in the Golgi apparatus, which allowed H₂S in the Golgi apparatus to be successfully imaged in RM-TGL mode.     

Impedimetric DNA‐Based Biosensor for Silver Ions Detection with Hemin/G‐Quadruplex Nanowire as Enhancer

A DNA‐based biosensor was reported for detection of silver ions (Ag⁺) by electrochemical impedance spectroscopy (EIS) with [Fe(CN)₆]^4?/3? as redox probe and hybridization chain reaction (HCR) induced hemin/G‐quadruplex nanowire as enhanced label. In the present of target Ag⁺, Ag⁺ interacted with cytosine‐cytosine (C? C) mismatch to form the stable C? Ag⁺? C complex with the aim of immobilizing the primer DNA on electrode, which thus triggered the HCR to form inert hemin/G‐quadruplex nanowire with an amplified EIS signal. As a result, the DNA biosensor showed a high sensitivity with the concentration range spanning from 0.1 nM to 100 µM and a detection limit of 0.05 nM.     

Design of a Novel Sort of Luminescent Terbium(III) Hybrid Materials with Potential Molecular Bridge

A kind of precursor molecule (abbreviated as EPDA–APMS) was synthesized by means of the amidation reaction of 5-ethylpyridine-2,3-dicarboxylic acid (EPDA) with a crosslinking molecule (3-aminopropyl)trimethoxysilane (APMS). Then the hybrid materials were obtained by reaction of this kind of monomer (EPDA–APMS), tetraethoxysilane (TEOS) and Tb(NO₃)₃·6H₂O by an in-situ sol-gel process, resulting in a novel molecular hybrid material (named as Tb–EPDA–APMS) with double chemical bonds (Tb–O coordination bond and Si–O covalent bond). Ultraviolet absorption, phosphorescence, and fluorescence spectra were applied to characterize the photophysical properties of the obtained hybrid material. The strong luminescence of Tb³⁺ substantiates optimum energy match and effective intramolecular energy transfer between the triplet state energy of modified ligand bridge and emissive energy level of Tb³⁺.     

Design of a Novel Sort of Luminescent Terbium(III) Hybrid Materials with Potential Molecular Bridge

Summary. A kind of precursor molecule (abbreviated as EPDA–APMS) was synthesized by means of the amidation reaction of 5-ethylpyridine-2,3-dicarboxylic acid (EPDA) with a crosslinking molecule (3-aminopropyl)trimethoxysilane (APMS). Then the hybrid materials were obtained by reaction of this kind of monomer (EPDA–APMS), tetraethoxysilane (TEOS) and Tb(NO₃)₃·6H₂O by an in-situ sol-gel process, resulting in a novel molecular hybrid material (named as Tb–EPDA–APMS) with double chemical bonds (Tb–O coordination bond and Si–O covalent bond). Ultraviolet absorption, phosphorescence, and fluorescence spectra were applied to characterize the photophysical properties of the obtained hybrid material. The strong luminescence of Tb³⁺ substantiates optimum energy match and effective intramolecular energy transfer between the triplet state energy of modified ligand bridge and emissive energy level of Tb³⁺.     

Solvent-dependent turn-on probe for dual monitoring of Ag and Zn in living biological samples

A novel, solvent-dependent “off–on” probe with benzoylthiourea moiety as the functional receptor and fluorescein as the fluorophore was designed for monitoring of Ag⁺ in EtOH–H₂O (2:8, v/v) solution and Zn²⁺ in CH₃CN–H₂O (2:8, v/v) solution at physiological range with sufficient selectivity and sensitivity. The Ag⁺ promoted desulfurization of thiosemicarbazide functionality in formation of the 1,3,4-oxadiazole and the coordination of Zn²⁺ to the O atom and N atom of the spoirolactam moiety and the S atom of the benzoylthiourea moiety were investigated to be the power that promoted the fluorescent enhancement. This probe was tested highly suitable for mapping Ag⁺ and Zn²⁺ in living human osteosarcoma MG-63 cells and microbial cell–EPS–mineral aggregates, thus, providing a wonderful candidate for tracking Ag⁺ and Zn²⁺ in biological organisms and processes.     

Single-fluorophore-based fluorescent probes enable dual-channel detection of Ag and Hg with high selectivity and sensitivity

A new type of fluorescent probe capable of detecting Ag⁺ and Hg²⁺ in two independent channels was developed in the present work. Specifically, in CH₃CN–MOPS mixed solvents with CH₃CN/MOPS ratio (v/v) of 15/85, this type of probe fluoresced weakly, and the addition of Ag⁺ remarkably induced fluorescence enhancement of the probe. In CH₃CN–MOPS mixed solvents with the percentage of CH₃CN increased up to 65%, the probe was highly fluorescent and addition of Hg²⁺ dramatically induced the fluorescence quenching. Thus, using such single-fluorophore-based probe and tuning the polarity of the mixed solvent, Ag⁺, and Hg²⁺ can be detected in independent channels with high selectivity and sensitivity. As a result, the mutual interference usually encountered in most cases of Ag⁺ and Hg²⁺ sensing owing to the similar fluorescence response that these two ions induced, can be effectively circumvented by using the probes developed herein.     

Poly(arginine)‐Selective Coprecipitation Properties of Self‐Assembling Apoferritin and Its Tb3+ Complex: A New Luminescent Biotool for Sensing of Poly(arginine) and Its Protein Conjugates

The apoferritin protein and apoferritin–Tb³⁺ complex were demonstrated to form oligomeric and polymeric self‐assemblies in neutral aqueous solutions, based on characterization by using luminescence and UV/Vis spectroscopy, dynamic light scattering, and transmission electron microscopy. Addition of a 20‐mer or higher poly(arginine) to the solution resulted in coprecipitation through nanoscale interactions, while biological proteins and other poly(amino acids) rarely yielded precipitates under the conditions employed. The apoferritin–Tb³⁺ complex assembly exhibited a particularly long‐lived green luminescence in aqueous solution, and its poly(arginine)‐selective precipitation behavior was followed by monitoring the changes in luminescence. The poly(arginine)‐tagged albumin precipitated selectively and quantitatively, so that the apoferritin–Tb³⁺ complex can function as a new luminescent biotool for the sensing of poly(arginine) and its protein conjugates.     

Lanthanide-centered inorganic/organic hybrids from functionalized 2-pyrrolidinone-5-carboxylic acid bridge: Covalently bonded assembly and luminescence

A series of organic-inorganic hybrid material with chemically bonding have been prepared through the precursor (PDCA-Si) derived from 2-pyrrolidinone-5-carboxylic acid, which exhibits a self-organization cooperation interaction under the coordination to RE³⁺ (Eu³⁺, Tb³⁺). The pure organic silica hybrids (PDCA-Si) without RE³⁺ presents the small particle size and main blue luminescence with maximum peak 462 nm occupying a broad band from 425 to 550 nm. When Eu³⁺ and Tb³⁺ are introduced, the particle size of the hybrids increases, indicating the coordination effect has influence on the microstructure of hybrids. Besides, the corresponding Eu and Tb hybrids (Eu-PDCA-Si, Tb-PDCA-Si) show the characteristic red and green luminescence of Eu³⁺ and Tb³⁺, respectively, which suggests that the efficient intramolecular energy transfer process take place between carboxylic groups and lanthanide ions take place. The luminescence lifetimes and quantum efficiencies of them are determined and energy transfer efficiency between PDCA-Si and Eu³⁺ (Tb³⁺) is calculated.     

Luminescence determination of sodium and potassium using molecular sensors on the basis of terbium(III) complexes of 4-carboxybenzocrown ethers

The spectral luminescent properties of terbium(III) complexes of 4-carboxybenzo-15-crown-5 (L₁) and 4-carboxybenzo-18-crown-6 (L₂) are studied. The quenching of the luminescence of lanthanide by alkali metal ions is discovered, which is referred to as the formation of mixed Tb(III)-L₁-Na⁺ and Tb(III)-L₂-K⁺ complexes. The complexes are useful as molecular sensors for the luminescence determination of Na⁺ and K⁺ with the detection limits 1.5 and 25.0 μg/mL. Using the Tb(III)-L₁ complex, sodium can be determined in the presence of a 1000-fold excess of potassium. The developed procedures are utilized for the determination of KCl in the Kalipoz medication in tablet form and the total sodium salts (NaCl, NaHCO₃) in the Trisol solution for infusions.