Lanthanide-based Probes Research Articles

Lanthanide-Based Probes for Imaging Detection of Enzyme Activities by NIR Luminescence, T1- and ParaCEST MRI.

Applying a single molecular probe to monitor enzymatic activities in multiple, complementary imaging modalities is highly desirable to ascertain detection and to avoid the complexity associated with the use of agents of different chemical entities. We demonstrate here the versatility of lanthanide (Ln3+) complexes with respect to their optical and magnetic properties and their potential for enzymatic detection in NIR luminescence, CEST and T1 MR imaging, controlled by the nature of the Ln3+ ion, while using a unique chelator. Based on X-ray structural, photophysical, and solution NMR investigations of a family of Ln3+ DO3A-pyridine model complexes, we could rationalize the luminescence (Eu3+, Yb3+), CEST (Yb3+) and relaxation (Gd3+) properties and their variations between carbamate and amine derivatives. This allowed the design of probes which undergo enzyme-mediated changes detectable in NIR luminescence, CEST and T1-weighted MRI, respectively governed by variations in their absorption energy, in their exchanging proton pool and in their size, thus relaxation efficacy. We demonstrate that these properties can be exploited for the visualization of β-galactosidase activity in phantom samples by different imaging modalities: NIR optical imaging, CEST and T1-weighted MRI.

Transmembrane transport of fluoride studied by time-resolved emission spectroscopy.

Here we present a new method to monitor fluoride transmembrane transport into liposomes using a europium(III) complex. We take advantage of the long emission lifetime of this probe to measure the transport activity of a fluorescent transporter. The high sensitivity, selectivity, and versatility of the assay allowed us to study different types of fluoride transporters and unravel their mechanisms of action.

Lanthanide-based probe for imaging and inhibition of LMP1-ralated cancers

Lanthanide-based probe for imaging and inhibition of LMP1-ralated cancers

E3 Ubiquitin Ligase SPL2 Is a Lanthanide-Binding Protein.

The SPL2 protein is an E3 ubiquitin ligase of unknown function. It is one of only three types of E3 ligases found in the outer membrane of plant chloroplasts. In this study, we show that the cytosolic fragment of SPL2 binds lanthanide ions, as evidenced by fluorescence measurements and circular dichroism spectroscopy. We also report that SPL2 undergoes conformational changes upon binding of both Ca2+ and La3+, as evidenced by its partial unfolding. However, these structural rearrangements do not interfere with SPL2 enzymatic activity, as the protein retains its ability to auto-ubiquitinate in vitro. The possible applications of lanthanide-based probes to identify protein interactions in vivo are also discussed. Taken together, the results of this study reveal that the SPL2 protein contains a lanthanide-binding site, showing for the first time that at least some E3 ubiquitin ligases are also capable of binding lanthanide ions.

A ratiometric lanthanide-free fluorescent probe based on two-dimensional metal-organic frameworks and carbon dots for the determination of anthrax biomarker.

Alanthanide-free fluorescent probe has been constructed for the first timebased on two-dimensional metal-organic frameworks (2D MOFs) and carbon dots (CDs) for ratiometric determination of dipicolinic acid (DPA), the biomarker of Bacillus anthracis. The fluorescence intensity at 659nm increased due to the release of organic ligands TCPP resulting from the selective interaction between DPA and Zn2+ of 2D MOFs. CDs provided a reference signal at 445nm which was almost unaffected, realizing self-calibration DPA sensing. F659/F445 versus the concentration of DPA shows good linear relationships in the range 0.01-0.2μM and 0.2-10μM under 390-nm excitation, with adetection limit of 7nM. The ratiometric probe was prepared from 2D lanthanide-free MOFs so that the drawbacks of lanthanide-based probes were overcome. The proposed sensing system was successfully applied to the determination of DPA in spiked biological samples. These results suggest that a novel, simple, and selective strategy of determining DPA with 2D lanthanide-free MOFs is implemented. Graphical abstract Zn-TCPP nanosheets and a blue carbon dots (b-CDs) are synthesized to construct the ratiometric probe, which can exhibit fluorescence at 445and 659nm with 390-nm excitation. Dipicolinic acid (DPA) can deprive the junction ions of Zn-TCPP nanosheets, triggering the collapse ofZn-TCPP nanosheets. The fluorescence at 659nm is enhanced due to the release of TCPP, while the peak of b-CDs at 445nm is almost not affected. Thus, the fluorescence intensity ratio (F659/F445) can serve as the response signal for sensitive DPA sensing.

Time-Resolved Terbium-Based Probe for the Detection of Zinc(II) Ions: Investigation of the Formation of a Luminescent Ternary Complex.

Because of their unique photochemical and photophysical properties, luminescent lanthanide-based complexes have long captivated chemists. In recent years, the number of reports of luminescent lanthanide complex-based probes for monitoring of biological and environmental processes has dramatically increased, namely, because of their selectivity for particular analytes, lower limits of detection, and the fact that they allow monitoring of analytes in real time. Lanthanide-based probes need to be paired with an appropriate antenna/sensitizer to allow maximum energy transfer, with the antenna typically covalently attached to the stable lanthanide chelate. We have recently investigated "dark" lanthanide-based probes where the sensitizer is not covalently linked to the lanthanide chelate. Herein we report the use of a luminescent lanthanide-based probe system for the detection of Zn2+ ions based on the formation of a ternary complex between a "dark" terbium complex, lumazine, and Zn2+. The terbium(III)-based probe incorporates a 1,4,7,10-tetraazacyclododecane-1,4,7,10-triacetic acid macrocyclic chelator covalently attached to a cyclen moiety, which is the Zn2+ ion binding group. In the presence of Zn2+ ions and lumazine (a strongly UV-absorbing sensitizer), a 1:1:1 ternary complex forms. The resulting complex is highly luminescent and selective for Zn2+ ions over other cations of environmental significance. Furthermore, with a limit of detection of 1.2 μM, this probe can detect the level of chronic zinc(II) concentrations denoted by the U.S. Environmental Protection Agency.

Luminescent Lanthanide-Based Probes for the Detection of Nitroaromatic Compounds in Water.

A new mixed pyridyl–carboxylate ligand with two picolinate chromophores and a flexible linear spacer, potassium 2,2′-(butane-1,4-diylbis((pyridin-2-ylmethyl)azanediyl))diacetate (K2bpbd), which is obtained in high yield and spectroscopically characterized, has been utilized to make new lanthanide complexes, namely, [Ln(bpbd) (H2O)2(NO3)]·xH2O, where Ln = Tb (1) and x = 6, Ln = Sm (2) and x = 7, and Ln = Dy (3) and x = 7. These complexes have been extensively characterized by various spectroscopic techniques (UV–vis and Fourier transform infrared spectroscopy), elemental analyses, thermogravimetric analysis, field emission scanning electron microscopy, and powder X-ray diffraction. These show very intense characteristic luminescence features that confirm the antenna effect of the ligand on the metal center. These complexes have been utilized for the detection of various nitroaromatic compounds. Among these three complexes, 1 is found to be the best for the selective sensing of 2,4,6-trinitrophenol in water with a detection limit of (0.35 ± 0.05) ppm. Its Stern–Volmer constant, KSV [(5.48 ± 0.1) × 104 M–1], is one of the highest among similar sensors reported so far.

Time-Gated Luminescence Detection of Enzymatically Produced Hydrogen Sulfide: Design, Synthesis, and Application of a Lanthanide-Based Probe.

Hydrogen sulfide (H2S) is now recognized as an important gaseous transmitter that is involved in a variety of biological processes. Here, we report the design and synthesis of a luminescent lanthanide biosensor for H2S, LP2-Cu(II)-Ln(III), a heterobinuclear metal complex that uses Cu(II) decomplexation to control millisecond-scale-lifetime-Tb(III)- or Eu(III)-emission intensity. LP2-Cu(II)-Ln(III) responded rapidly, selectively, and with high sensitivity to aqueous H2S. The probe's potential for biological applications was verified by measuring the H2S generated by the slow-releasing chemical-sulfide-donor GYY4147, by cystathionine γ-lyase (CSE), and by Na2S-stimulated HeLa cells.

A luminogenic lanthanide-based probe for the highly selective detection of nanomolar sulfide levels in aqueous samples.

A bimetallic terbium(iii)/copper(ii) complex (Tb-1·Cu2+) for the time-gated luminescent detection of hydrogen sulfide in aqueous samples is reported. The probe shows excellent selectivity towards HS- over various anions and cations, including the ions common to natural waterways and waste water samples, displaying a 73-fold increase in luminescence in the presence of sulfide. The probe exhibits extremely fast reaction times and a low limit of detection (130 nM). The probe was used to quantify sulfide in an industrial "sour water" sample, with the result in excellent agreement with those from two independent assay methods (methylene blue and AzMC).

Fluorescence and Electrochemical Sensing of Pesticides Methomyl, Aldicarb and Prometryne by the Luminescent Europium-3-Carboxycoumarin Probe

This work describes the application of time resolved fluorescence in microtiterplates and electrochemical methods on glassy carbon electrode for investigating the interactions of europium-3-carboxycoumarin with pesticides aldicarb, methomyl and prometryne. Stern-volmer studies at different temperatures indicate that static quenching dominates for methomyl, aldicarb and prometryne. By using Lineweaver-Burk equation binding constants were determined at 303 K, 308 K and 313 K. A thermodynamic analysis showed that the reaction is spontaneous with ΔG being negative. The enthalpy ΔH and the entropy ΔS of reactions were all determined. A time-resolved (gated) luminescence-based method for determination of pesticides in microtiterplate format using the long-lived europium-3-carboxycoumarin has been developed. The limit of detection is 4.80, 5.06 and 8.01 μmol L(-1) for methomyl, prometryne and aldicarb, respectively. This is the lowest limit of detection achieved so far for luminescent lanthanide-based probes for pesticides. The interaction of the probe with the pesticides has been investigated using cyclic voltammetry (CV), differential pulse polarography (DPP), square wave voltammetry (SWV) and linear sweep voltammetry (LSV) on a glassy carbon electrode in I = 0.1 mol L(-1) p-toluenesulfonate at 25 °C. The diffusion coefficients of the reduced species are calculated. The main properties of the electrode reaction occurring in a finite diffusion space are the quasireversible maximum and the splitting of the net SWV peak for Eu(III) ions in the ternary complex formed . It was observed that the increase of the cathodic peak currents using LSV is linear with the increase of pesticides concentration in the range 5 × 10(-7) to 1 × 10(-5) mol L(-1). The detection limit (DL) were about 1.01, 2.23 and 1.89 μmol L(-1) for aldicarb, methomyl and prometryne, respectively. In order to assess the analytical applicability of the method, the influence of various potentially interfering species was examined. Influence of interfering species on the recovery of 10 μmol L(-1) pesticides has been investigated.

A long-lived luminescence and EPR bimodal lanthanide-based probe for free radicals

We developed a novel spin-labeled terbium complex Tb(3+)/cs124-DTPA-TEMPO (1) by covalently labeling a nitroxide radical on the terbium complex for monitoring free radicals of various areas. This lanthanide complex probe shows a high EPR signal which resulted from the nitroxide radical moiety, and is weakly luminescent which resulted from the intramolecular quenching effect of the nitroxide radical on sensitised terbium luminescence. The intensity of both the EPR and luminescence can be modulated by eliminating the paramagnetism of the nitroxide radical through recognition of a carbon-centered radical analyte and thus gives a quantification of the analyte. We have preliminarily applied this probe in the luminescent detection of model carbon-centered radicals and hydroxyl radicals (·OH). This probe is water-soluble and contains lanthanide-luminescence properties, favorable for the time-resolved luminescence technique. The investigation of the intramolecular quenching process has showed that the labeled nitroxide radical quenches multiple excited states of the terbium complex, resulting in highly efficient quenching of terbium luminescence. This probe is the first example of intramolecular modulation of lanthanide luminescence by a nitroxide radical.

Microtiterplate phosphate assay based on luminescence quenching of a terbium complex amenable to decay time detection

We describe a terbium-ligand complex (TbL) for a microtiterplate assay for phosphate (P) in the 0.3–100 μmol L −1 range based on luminescence quenching. As the pH optimum is at neutral pH (7.4) the probe is quenched by both, primary (H 2PO 4 −) and secondary phosphate (HPO 4 2−). The LOD is 110 nmol L −1. A Stern–Volmer study revealed that quenching is mostly static. Due to the ms-decay time of TbL, the first luminescence lifetime assay for phosphate could also be developed. The lifetime-based calibration plot is linear between 0.5 and 5 μmol L −1 of P. The effect of various surfactants on assay performance and a study on interferents are presented. The probe was successfully applied to determination of P in commercial plant fertilizers and validated against the molybdenum blue test. The probe is the most sensitive lanthanide-based probe for phosphate.

Detection of nanomolar concentrations of copper(II) with a Tb-quinoline-2-one probe using luminescence quenching or luminescence decay time

We present a time-resolved (gated) luminescence-based method for determination of Cu 2+ ions in microtiterplate format in the nanomolar concentration range using the novel long-lived terbium-[1-methyl-4-hydroxy-3-(N-2-ethyl-5-aminothiadiazolyl-)-carbamoyl-quinoline-2-one] (TbL) complex. The probe works best in Tb:L = 1:2 stoichiometry at neutral pH. The dynamic range is from 10 to 300 nmol L −1 of Cu 2+ and the limit of detection is 4.3 nmol L −1. This is the lowest limit of detection achieved so far for luminescent lanthanide-based probes for copper. It is shown that gating can efficiently suppress intense, short decaying background fluorescence e.g. that of Rhodamine 6G. The assay can be performed by measurement of luminescence decay time, as well. Stern-Volmer studies indicate that static quenching dominates over dynamic quenching. TbL 2 was tested for the effect of some relevant interferents and the assay was applied to the determination of copper in tap water samples. The results achieved were in good agreement with those of a reference method.

Principles of responsive lanthanide-based luminescent probes for cellular imaging

The advent of chemical tools for cellular imaging--from organic dyes to green fluorescent proteins--has revolutionized the fields of molecular biology and biochemistry. Lanthanide-based probes are a new player in this area, as the last decade has seen the emergence of the first responsive luminescent lanthanide probes specifically intended for imaging cellular processes. The potential of these probes is still undervalued by the scientific community. Indeed, this class of probes offers several advantages over organic dyes and fluorescent proteins. Their very long luminescence lifetimes enable quantitative spatial determination of the intracellular concentration of an analyte through time-gating measurements. Their emission bands are very narrow and do not overlap, enabling the simultaneous use of multiple lanthanide probes to quantitatively detect several analytes without cross-interference. Herein we describe the principles behind the development of this class of probes. Sensors for a desired analyte can be designed by rationally manipulating the parameters that influence the luminescence of lanthanide complexes. We will discuss sensors based on varying the number of inner-sphere water molecules, the distance separating the antenna from the lanthanide ion, the energies of excited states of the antenna, and PeT switches.

Lanthanide-based probes for MR-Molecular Imaging investigations

Molecular and cellular imaging is a relatively young field that is rapidly changing our approach towards understanding and solving problems in in vivo diagnoses with innovative solutions.

Principles and biophysical applications of lanthanide-based probes.

Using luminescent lanthanides, instead of conventional fluorophores, as donor molecules in resonance energy transfer measurements offers many technical advantages and opens up a wide range of new applications. Advantages include farther measurable distances ( approximately 100 A) with greater accuracy, insensitivity to incomplete labeling, and the ability to use generic relatively large labels, when necessary. Applications highlighted include the study of ion channels in living cells, protein-protein interaction in cells, DNA-protein complexes, and high-throughput screening assays to measure peptide dimerization associated with DNA transcription factors and ligand-receptor interactions.