Luminescent Probes Research Articles

Spectral imaging in microscopy aids evaluation of the luminescent probe behaviour of europium complexes

In a series of structurally related cationic Eu(III) triamide complexes, the analysis of variations in emission lifetime and spectral signature as a function of probe environment has elucidated the nature of changes to probe speciation. The cationic complexes exhibit an intrinsic tendency to localise in cellular nucleoli or the lysosomes, providing key information in the design and evaluation of related targeted probes. Each of the three complexes studied possesses a coordinated water molecule in aqueous media, that is absent in organic solvents or is displaced by the addition of protein. The complex observed in cellulo is probably a protein-bound Eu complex.

A pyrazole-functional 3D cobalt-organic framework for fluorescence detection of Cu2+ and Hg2+

A new MOFs luminescent probe with the formula of [Co3(L)2(H2O)6]n (1) was synthesized via a solvothermal reaction with a triangular ligand 1,3,5-(tris(1-(4-carboxyphenyl)-1H-pyrazol-3-yl))benzene (H3L) and Co nitrate. Single-crystal X-ray diffraction analysis revealed compound 1 features a 3D network, which was constructed by 1D Co-O chains and μ5-connected L3− ligands. It is noteworthy that pyrazole N atoms of the ligand were uncoordinated in the framework. Detailed luminescent investigations reveal that compound 1 could sever as a highly selective and sensitive “turn off” luminescent probe toward Cu2+ or Hg2+ in DMA solution. The possible luminescent quenching mechanism of compound 1 by Cu2+ or Hg2+ can be attributed to the weak Lewis acid-base interaction between Cu2+ or Hg2+ and pyrazole N atoms.

Specific and Long-Term Luminescent Monitoring of Hydrogen Peroxide in Tumor Metastasis.

Luminescent monitoring of endogenous hydrogen peroxide (H2 O2 ) in tumors is conducive to understanding metastasis and developing novel therapeutics. The clinical transformation is obstructed by the limited light penetration depth, toxicity of nano-probes, and lack of long-term monitoring modes of up to days or months. New monitoring modes are introduced via specific probes and implantable devices, which can achieve real-time monitoring with a readout frequency of 0.01 s or long-term monitoring for months to years. Near-infrared dye-sensitized upconversion nanoparticles (UCNPs) are fabricated as the luminescent probes, and the specificity to reactive oxygen species is subtly regulated by the self-assembled monolayers on the surfaces of UCNPs. Combined with the passive implanted system, a 20-day monitoring of H2 O2 in the rat model of ovarian cancer with peritoneal metastasis is achieved, in which the limited light penetration depth and toxicity of nano-probes are circumvented. The developed monitoring modes show great potential in accelerating the clinical transformation of nano-probes and biochemical detection methods.

Luminescent Sensor with High Sensitivity and Selectivity for Amikacin Detection in a Serum using a Unique Gallium-Organic Framework.

Amikacin is a widely used antibiotic in the treatment of Gram-negative bacteria, but high concentrations of amikacin can cause cochlear nerve damage. Therefore, accurate and quick detection of the concentration of amikacin is desired and important. In this work, we have synthesized a new gallium-organic framework {[(CH3)2(NH2)Ga(PPTA)]·0.5DMF}n (1) (H4PPTA = 4,4',4″,4″'-(1-4-phenlene-bis(pyridine-4,2,6-triyl)) with good solvent and pH stabilities. A structure analysis reveals that 1 is a twofold interpenetrated framework exhibiting a large 1D square aperture with a size of 10.8 Å × 14 Å. The experimental results show that 1 can be used as a stable, fast, and recyclable luminescent probe for the detection of amikacin in aqueous solution and serum. The limit of detection is 2.9 × 10-7 mol/L, which is lower than the harmful concentration of amikacin in human serum. This is the first example of a metal-organic framework used for luminescence sensing of amikacin.

CsPbBr3 nanocrystals as luminescent probe for in situ detection of chloride and iodide ions in water

All-inorganic cesium lead halide (CsPbX3, X = Cl, Br, I) Perovskite nanocrystals (PNCs) are promising new luminescent nanomaterials. However, PNCs are less stable in ambient environments. The fully encapsulated protective layer greatly improves the stability but limits direct contact with substances in the environment, leading to great challenges for luminescent probe applications. We developed a simple approach that hydrogen-bond cross-linking reinforcement to deal with the challenge. Target ACD-PNCs, which use β-CD (β- cyclodextrin) as the ligand with addition of Arginine, were prepared by adding arginine to an ethanol solution of CsPbBr3 stabilized by β-CD. The ACD-PNCs have a luminescence efficiency of 82% and show good stability in external environments including high temperature, humidity, and ethanol–water mixed solvents. It is worth noting that neither arginine nor cyclodextrin alone could have allowed PNCs to perform so well. More interestingly, the hydrogen-bond network permits the passage of chloride and iodide ions. Through the response of luminescence color upon ion exchange, the ACD-PNCs can detect aqueous Cl− and I− with good selectivity and sensitivity. Under optimum conditions, the LOD and % RSD were determined as 3.2*10−6 M and 5.7% for Cl−, 9.0*10−6 M and 6.7% for I−, respectively. To identify halide ions in samples like sweat, saliva, and kelp, conveniently prepared ACD-PNCs test strips were employed. This work provides insights into the design and development of perovskite probes capable of detection in aqueous solution, and also demonstrates the importance of rapidly forming hydrogen-bonding networks when studying such sensing systems.

Novel near-infrared frequency up-conversion luminescence probe for monitoring biothiols in vitro and in vivo

Biothiols including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) play important roles in the antioxidant activity of cells, and a variety of diseases could be linked to their abnormal levels. Frequency up-conversion luminescence (FUCL) probes have low background fluorescence and cause low tissue damage; thus it is less harmful than Stokes shift luminescence probes, the traditional fluorescence probes. However, the utilization of FUCL probes for detection of biothiols has rarely been reported. In this work, we designed and synthesized a near-infrared (NIR) xanthene derivative IFU-1 and used as a frequency up-conversion luminescence probe to detect biothiols. The probe IFU-1 had high selectivity for biothiols and exhibited enhanced FUCL signals in response to them. In addition, it has extremely low limit of detection with regards to different biothiols: 4.8 nM for Cys; 6.2 nM for Hcy, and 9.5 nM for GSH, which are about 10 times lower than the detection limit of traditional excitation methods (63 nM for Cys, 31 nM for Hcy, and 76 nM for GSH). This work presents a novel approach for constructing FUCL biosensors.

Thermally activated upconversion luminescence and ratiometric temperature sensing under 1064 nm/808 nm excitation

In this research, a thermally activated upconversion luminescence (UCL) probe with ratiometric temperature sensing under 1064 nm and 808 nm excitation was designed. Especially, Nd3+, Tm3+ and Ce3+ were doped in rare earth nanoparticles (RENPs) as UCL modulators. By optimizing the elements and ratios, the excitation wavelength is successfully modulated to 1064 nm excitation with UCL intensity enhanced. Additionally, the prepared RENPs have a significant temperature response at 1064 nm excitation and can be used for thermochromic coatings. The intensity ratio of three-photon UCL (1064 nm excitation) to two-photon UCL (808 nm excitation) as an exponential function of temperature can be used as a ratiometric temperature detector. Therefore, this designed thermochromic coatings may enable new applications in optoelectronic device and industrial sensor.

Glutathione-Activated Emission of Ultrasmall Gold Nanoparticles in the Second Near-Infrared Window for Imaging of Early Kidney Injury.

Biomarker-activatable luminescent probes with high sensitivity and specificity show great promise in advanced bioimaging applications. However, the lack of stable biomarkers at an early stage is currently a major obstacle for sensitive early disease imaging. Herein, we develop a facile in vivo ligand exchange strategy to achieve renal-clearable activatable luminescent gold nanoparticles (AuNPs), which are independent of biomarkers for sensitive and long-time imaging of early kidney injury. Significantly activated emission in the second near-infrared region (∼1026 nm) is realized from the ligand exchange of triphenylphosphine-3,3',3″-trisulfonic acid (TPPTS)-coated AuNPs (∼1.4 nm, TPPTS-AuNPs) with quantitative amounts of glutathione (GSH). The abundant GSH in cells, particularly in liver sinusoids, is then demonstrated successfully to activate the emission of TPPTS-AuNPs with an extremely low background for both cell imaging and in vivo visualization of visceral organs (e.g., liver and kidneys). In addition, the in vivo GSH-exchanged TPPTS-AuNPs show enhanced interactions with acidic renal tubular epithelial cells, resulting in sensitive (contrast index, ∼3.9) and long-time (>6.5 h) noninvasive monitoring of acidosis-induced early kidney injury. This facile ligand exchange strategy opens new possibilities for designing activatable luminescent probes independent of biomarkers for earlier disease diagnosis and treatment.

Development of a sensitive luminescent probe to uncover new BRD4 inhibitors in living cells

Bromodomain-containing protein 4 (BRD4) is a reader of acetylated histones that regulates the invasion, metastasis and proliferation of cancer. Inhibition of BRD4 activity is an emerging strategy for anticancer. In this study, an iridium based-luminescent probe for screening BRD4 inhibitors in cellulo was developed. The K293 probe was designed by linking a BRD4 nuclear translocation inhibitor as a “binding unit” to an iridium complex as a luminescent “signal unit”. K293 selectively binds to BRD4 in living cancer cells. Candidate compounds compete with K293 for BRD4, resulting in a decrease in luminescence signal. The long luminescence lifetime of K293 allows its luminescence signal to be distinguished from interfering fluorescence using time-resolved techniques in order to improve sensitivity. Hence, even potential BRD4 inhibitors that are undetectable by conventional fluorescence methods can be identified. As a proof-of-concept, Azelastine, an FDA-approved histamine 1 (H1)antagonist was identified to be a potential BRD4 inhibitor using the K293 probe. Azelastine binds to BRD4 protein in the cytoplasm to prevent its translocation into the nucleus, and suppresses cancer cell growth and migration. The results demonstrated that the probe could be useful for the future drug repurposing.

Localization and chemical speciation of europium(III) in Brassica napus plants

For the reliable safety assessment of repositories of highly radioactive waste, further development of the modelling of radionuclide migration and transfer in the environment is necessary, which requires a deeper process understanding at the molecular level. Eu(III) is a non-radioactive analogue for trivalent actinides, which contribute heavily to radiotoxicity in a repository. For in-depth study of the interaction of plants with trivalent f elements, we investigated the uptake, speciation, and localization of Eu(III) in Brassica napus plants at two concentrations, 30 and 200 µM, as a function of the incubation time up to 72 h. Eu(III) was used as luminescence probe for combined microscopy and chemical speciation analyses of it in Brassica napus plants. The localization of bioassociated Eu(III) in plant parts was explored by spatially resolved chemical microscopy. Three Eu(III) species were identified in the root tissue. Moreover, different luminescence spectroscopic techniques were applied for an improved Eu(III) species determination in solution. In addition, transmission electron microscopy combined with energy-dispersive X-ray spectroscopy was used to localize Eu(III) in the plant tissue, showing Eu-containing aggregates. By using this multi-method setup, a profound knowledge on the behavior of Eu(III) within plants and changes in its speciation could be obtained, showing that different Eu(III) species occur simultaneously within the root tissue and in solution.

Tb-MOF-based luminescent recovery probe for rapid and facile detection of an anthrax biomarker

Rapidly detecting 2, 6-dipicolinic acid (DPA, an anthrax biomarker) in a highly sensitive manner is vital due to DPA being highly lethal to human beings and animals. However, most reported DPA probes are ‘‘turn-on’ type, while luminescent recovery probes (LRPs) are still rare. Herein, a unique Tb-MOF (1) LRP was tailor-made, and its function is achieved via an energy transfer regulation strategy. In 1, the characteristic luminescence from Tb3+ is not sensitized due to the lack of energy transfer from the carefully chosen ligand that also induces steric effects to allow solvent molecules to be coordinated to Tb3+. During detection, DPA replaces the solvent molecules and thus effectively sensitizes the emission from Tb3+, achieving recovery response. 1 exhibits highly selective sensing of DPA down to 1.7 μM, and displays an obvious luminescence color change visible to naked eyes. Furthermore, a regular smartphone platform installed with a Color Recognizer App can achieve sensitive, real-time, and on-site detection of DPA. The probe can also be used for the effective detection of DPA in tap water, rainwater, and human serum. The work not only provides a route to the preparation of recovery probes but also proves the potential of such probes.

Orientational Control of Circularly Polarized Luminescence from Pyrene Clusters by Using a DNA Scaffold.

We have investigated the chiroptical activities of pyrene clusters incorporated within a DNA duplex. Three pyrene derivatives were prepared on d-threoninol linkers to allow incorporation within a DNA strand. DNA scaffolds containing dimers, tetramers, and hexamers of the pyrene derivatives were prepared. The homodimers of 1- and of 4-pyrenecarboxylic acid, but not 2-pyrenecarboxylic acid, emitted intense circularly polarized luminescence signals. Although increasing the number of pyrene units weakened the signal, insertion of natural base pairs between two dimers enhanced its intensity. Interestingly, circularly polarized luminescence intensities varied non-monotonically depending on the number of intervening base pairs, thus indicating the importance of orientation between pyrene dimers. The results presented here could lead to the development of bright circularly polarized luminescence materials and probes.

Detecting phosphate using lysine-sensitized terbium coordination polymer nanoparticles as ratiometric luminescence probes.

Probes for detecting phosphate ions (Pi) are required for environmental monitoring and to protect human health. Here, novel ratiometric luminescent lanthanide coordination polymer nanoparticles (CPNs) were successfully prepared and used to selectively and sensitively detect Pi. The nanoparticles were prepared from adenosine monophosphate (AMP) and Tb3+, and lysine (Lys) was used as a sensitizer (through the antenna effect) to switch on Tb3+ luminescence at 488 and 544nm while Lys luminescence at 375nm was quenched because of energy transfer from Lys to Tb3+. The complex involved is here labeled AMP-Tb/Lys. Pi destroyed the AMP-Tb/Lys CPNs and therefore decreased the AMP-Tb/Lys luminescence intensity at 544nm and increased the luminescence intensity at 375nm at an excitation wavelength of 290nm, meaning ratiometric luminescence detection was possible. The ratio between the luminescence intensities at 544 and 375nm (I544/I375) was strongly associated with the Pi concentration between 0.1 and 6.0μM, and the detection limit was 0.08μM. The dual-emission reverse-change ratio luminescence sensing method can exclude environmental effects, so the proposed assay was found to be very selective. The method was successfully used to detect Pi in real water samples, and acceptable recoveries were found, suggesting that the method could be used in practice to detect Pi in water samples.

Development of a molecularly imprinted electrochemiluminescence sensor based on bifunctional bilayer structured ZIF-8-based magnetic particles for dopamine sensing

A bilayer-structured ZIF-8 composite with dual functions of sensing and recognition was synthesized, with ZIF-8 serving as an electrochemiluminescence (ECL) probe carrier and molecularly imprinted membrane to construct a molecularly imprinted electrochemiluminescence sensor. The inner layer was a ZIF-8 layer loaded with a luminescent probe, which was obtained by the reaction of zinc ions with 2-methylimidazole on the magnetic [email protected]2O4 surface in the presence of Ru(bpy)32+, the composite magnetic particle is marked as ZIF(Ru)/[email protected]2O4. The outer layer was a layer with recognition function using ZIF-8 as an imprinted membrane, which was obtained by a layer-by-layer self-assembly method on the surface of ZIF(Ru)/[email protected]2O4 with dopamine (DA) as a template molecule, which was marked as ZIF(MIP)/ZIF(Ru)/[email protected]2O4. After eluting the template molecules, the composite particle was immobilized on the surface of a magnetically controlled glassy carbon electrode (MGCE) to obtain a molecular imprinting (MIP) modified electrode. When dopamine molecules were re-adsorbed by the MIP, a charge/energy transfer between dopamine and Ru(bpy)32+ occurred. It subsequently led to the quenching of electrochemiluminescence, which was used as the basis for the detection of dopamine by a molecularly imprinted electrochemiluminescence sensor. When the dopamine concentration was in the range of 1.0 × 10−14 ∼ 5.0 × 10−10 mol/L, the ECL intensity change of the sensor and the dopamine concentration had a good linear relationship, and the detection limit was 4.8 × 10−15 mol/L. The molecularly imprinted electrochemiluminescence sensor was successfully applied to the detection of dopamine in human serum samples.

Bright and Photostable TADF‐Emitting Zirconium(IV) Pyridinedipyrrolide Complexes: Efficient Dyes for Decay Time‐Based Temperature Sensing and Imaging

AbstractLuminescence thermometry represents a technique of choice for measurements in small objects and imaging of temperature distribution. However, most state‐of‐the‐art luminescent probes are limited in spectral characteristics, brightness, photostability, and sensitivity. Molecular thermometers of the new generation utilizing air and moisture‐stable zirconium(IV) pyridinedipyrrolide complexes can address all these limitations. The dyes emit pure thermally activated delayed fluorescence without any prompt fluorescence and show a unique combination of attractive features: a) visible light excitation and emission in the orange/red region, b) high luminescence brightness (quantum yields ≈0.5 in toluene and 0.8–1.0 in polystyrene matrix), c) excellent photostability, d) suitability for two‐photon excitation and e) mono‐exponential decay on the order of tens to hundreds of microseconds with strongly temperature‐dependent lifetimes (between −2.5 and −2.9% K−1 in polystyrene at 25 °C). Immobilization in gas‐blocking polymers yields sensing materials for self‐referenced decay time read‐out that are manufactured in two common formats: planar optodes and water‐dispersible nanoparticles. Positively charged nanoparticles are demonstrated to be suitable for nanothermometry in live cells and multicellular spheroids. Negatively charged nanoparticles represent advanced analytical tools for imaging temperature gradients in samples of small volumes such as microfluidic devices.

Tough, Self-Healing, and UV Light-Switchable Luminescent Hydrogels with Reversible Stimuli-Responsive Properties for Cu2+

Stimuli-responsive luminescent hydrogels (LHs) are of great potential for applications in advanced luminescent sensors; however, structural optimizations and challenges in implementation still remain in their practical applications. Herein, we reported a promising and cooperative strategy to prepare smart LH actuators. Lanthanide(III)-based complexes (LnCs) and sulfur quantum dots (S-QDs) in this contribution are constructed in a cooperative manner; that is, (1) a noncovalent hydrogen bonding model between polyethylene glycol (PEG) in S-QDs and polyurethane (PU) endows LHs with interwoven double networks and improved the mechanical properties and (2) LnCs and S-QDs are two excellent emitting centers with different luminescent excitation properties, leading to the modulating emission colors of LHs by varying the UV irradiation between 254 and 365 nm. Meanwhile, the resultant LHs containing 3.26 wt % of PU possess good mechanical performance and self-healing capability. As a proof of application in stimuli response, our LHs can be served as a ratiometric luminescence probe to electively detect Cu2+ via exponentially correlating the emission intensity ratio of LnCs and S-QDs to the Cu2+ concentration. Remarkably, the obtained LHs also show reversible luminescence “On/Off” switch upon alternate exposure to Cu2+/glutathione (GSH) under 254 nm, while no obvious luminescent variation is observed under 365 nm.

Mitochondria-Targetable Ratiometric Time-Gated Luminescence Probe Activated by Selenocysteine for the Visual Monitoring of Liver Injuries.

Liver injury can result from various risk factors including diabetes, virus, alcohol, drugs, and other toxins, which is mainly responsible for global mortality and morbidity. Selenocysteine (Sec), as the main undertaker of selenium function in the life system, features prominently in a series of hepatic injuries and has close association with the pathological progression of liver injuries. Here, we report a mitochondria-targetable lanthanide complex-based probe, Mito-NPTTA-Tb3+/Eu3+, that can be used for accurately determining Sec in live cells and laboratory animals via the ratiometric time-gated luminescence (TGL) technique. This probe is composed of 2,2':6',2″-terpyridine-Tb3+/Eu3+ mixed complexes as the luminophore, 2,4-dinitrophenyl (DNP) as the responsive moiety and a lipophilic triphenylphosphonium cation (PPh3+) as the mitochondria-targeting moiety. Upon reaction with Sec, accompanied by the cleavage of DNP from the probe molecule, the I540/I690 ratio of the probe increased by 55 times, which enabled Sec to be detected with the ratiometric TGL method. After being incubated with living cells, the probe molecules were selectively accumulated in mitochondria to allow the mitochondrial Sec to be successfully imaged under the ratiometric TGL mode. Importantly, using this probe coupled with the ratiometric TGL imaging technique, the fluctuations of liver Sec in various liver injuries of model mice induced by diabetes, drug, toxin, and alcohol were precisely monitored, revealing that Sec plays an important antioxidant role during the oxidative stress process in liver injury, and the Sec levels have a close interrelationship with the degree of liver injury. All the results suggest that the new probe Mito-NPTTA-Tb3+/Eu3+ could be a potential tool for the accurate diagnosis of liver injury.

Fabrication of Eu3+-dipicolinic acid complex functionalized nanoSiO2 composites and their Langmuir-Blodgett films as visual fluorescence probe for tetracycline and oxytetracycline

Luminescent lanthanide complexes have attracted growing attention in the visual probe for detection of toxic and dangerous materials. Here, we report an interfacial self-assembly of Eu3+-dipicolinic acid complex functionalized nanoSiO2 composites (nanoSiO2PyTAEu) and their Langmuir-Blodgett (LB) films as well as the luminescent probes to tetracycline (TC) and oxytetracycline (OTC). Organic linkers and Eu3+ ions are anchored on the hydrophilic nanoSiO2 particles’ surface via the surface silanization, substitution and coordination reactions, so they exhibit high stability and well distribution in the solutions and LB films. Both the nanocomposites of nanoSiO2PyTAEu and their LB films show strong and enhanced red fluorescence emissions of Eu3+ ions when they are immersed in the aqueous TC solution, with the detection limit to 3.3 and 0.91 nmol/L, respectively. The present nanocomposites and LB films have the advantages of high sensitivity and stability.

Fluorescent Carbon Dots from Food Industry By-Products for Cell Imaging

Herein, following a circular economy approach, we present the synthesis of luminescent carbon dots via the thermal treatment of chestnut and peanut shells, which are abundant carbon-rich food industry by-products. As-synthesized carbon dots have excellent water dispersibility thanks to their negative surface groups, good luminescence, and photo-stability. The excitation-emission behaviour as well as the surface functionalization of these carbon dots can be tuned by changing the carbon source (chestnuts or peanuts) and the dispersing medium (water or ammonium hydroxide solution). Preliminary in vitro biological data proved that the samples are not cytotoxic to fibroblasts and can act as luminescent probes for cellular imaging. In addition, these carbon dots have a pH-dependent luminescence and may, therefore, serve as cellular pH sensors. This work paves the way towards the development of more sustainable carbon dot production for biomedical applications.

Long‐Lived Second Near‐Infrared Luminescent Probes: An Emerging Role in Time‐Resolved Luminescence Bioimaging and Biosensing

Long‐Lived Second Near‐Infrared Luminescent Probes: An Emerging Role in Time‐Resolved Luminescence Bioimaging and Biosensing