Lanthanide based dual-emission fluorescent probe for detection of mercury (II) in milk

A simple and stable dual-emission fluorescent system based on R6G/Eu-MOF for the rapid and sensitive determination of orientin

A stable dual-emission fluorescent system, R6G/Eu-MOF, was obtained by simple mixing Eu-MOF with fluorescent rhodamine 6G (R6G). This system not only achieved robust dual luminescence performance at 430 nm (Eu-MOF) and 555 nm (R6G) under single-wavelength excitation, but also endowed it with significantly improved fluorescence stability. Orientin (OT), a bioactive traditional Chinese medicine (TCM) component, was found to efficiently quench the dual fluorescent emissions via the synergistic effect of dynamic quenching, photo-induced electron transfer and molecular interactions. Therefore, a rapid fluorescent assay for OT was developed based on the variations in fluorescence signals at 430 nm and 555 nm, as well as the alterations in the ratio between these two signals. This method can achieve highly sensitive determination of OT in the linear range of 1.1-220 μM, with a LOD of 0.26 μM at 430 nm and 0.16 μM at 555 nm (3σ/N). The R6G/Eu-MOF hybrid exhibits significantly lower detection limits and a broader linear range for OT than either R6G or Eu-MOF alone. This work presents a simple strategy to improve the water stability of Eu-MOF and also provides a rapid analysis of small molecule drugs using a fluorescence approach based on a dual-emission MOF hybrid system.

Captivating nano sensors for mercury detection: a promising approach for monitoring of toxic mercury in environmental samples

Mercury, a widespread highly toxic environmental pollutant, poses significant risks to both human health and ecosystems. It commonly infiltrates the food chain, particularly through fish, and water resources via multiple pathways, leading to adverse impacts on human health and the environment. To monitor and keep track of mercury ion levels various methods traditionally have been employed. However, conventional detection techniques are often hindered by limitations. In response to challenges, nano-sensors, capitalizing on the distinctive properties of nanomaterials, emerge as a promising solution. This comprehensive review provides insight into the extensive spectrum of nano-sensor development for mercury detection. It encompasses various types of nanomaterials such as silver, gold, silica, magnetic, quantum dot, carbon dot, and electrochemical variants, elucidating their sensing mechanisms and fabrication. The aim of this review is to offer an in-depth exploration to researchers, technologists, and the scientific community, and understanding of the evolving landscape in nano-sensor development for mercury sensing. Ultimately, this review aims to encourage innovation in the pursuit of efficient and reliable solutions for mercury detection, thereby contributing to advancements in environmental protection and public health.

A portable test strip fabricated of luminescent lanthanide-functionalized metal-organic frameworks for rapid and visual detection of tetracycline antibiotics

Tetracycline antibiotics (TCs) are commonly used antibiotics in the treatment of infections, but their overuse has a negative impact on human health and ecosystems. Thus, the development of a facile and on-site visualization method for TC detection is necessary. Here, we propose the potential of using lanthanide-functionalized metal-organic framework (MOF) composites (Ag+/Tb3+@UiO-66-(COOH)2, ATUC) as a probe for the rapid detection of tetracycline (TC), chlortetracycline (CTC), oxytetracycline (OTC), and doxycycline (DOX) residues, in which UiO-66-(COOH)2 (UC) could be utilized to provide an interaction microenvironment, Tb3+ as recognition units and Ag+ as a fluorescence enhancer. Upon exposure to TCs, significant luminescence quenching of ATUC excited at 255 nm was observed due to the inner filter effect (IFE) and photo-induced electron transfer (PET), and the established strategy has a detection limit (LOD) of 11.0, 20.1, 9.1, and 22.5 nM for TC, CTC, OTC, and DOX, respectively. More importantly, given its portability and conspicuous luminescence color gradation variation, a portable test strip based on ATUC was manufactured and the results could be distinguished immediately by the naked eye and smartphone analysis, allowing for on-site rapid quantitative assay of TCs, not only in the laboratory but also in a point-of-care setting.

Dual-ligand lanthanide metal-organic framework probe for ratiometric fluorescence detection of mercury ions in wastewater

By serving dipyridylic acid (DPA) and 2,5-dihydroxyterephthalic acid (DHTA) as the biligands, a novel lanthanide (Eu3+) metal-organic framework (MOF) namely Eu-DHTA/DPA was prepared for specific Hg2+ fluorescence determination. The dual-ligand approach can endows the resulting luminescent MOF with dual emission of ratiometric fluorescence and uniform size. Eu3+ produces intense red fluorescence when activated by the ligand DPA, while the other ligand DHTA produces yellow fluorescence. Under 273 nm excitation, the presence of Hg2+ in the monitoring environment causes an increase in the intensity of the DHTA fluorescence peak at 559 nm and a decrease in the intensity of the Eu3+ fluorescence peak at 616 nm. Hg2+ effectively quenches the fluorescence emission of the central metal Eu3+ in Eu-DHTA/DPA at 616 nm through a dynamic quenching effect. This recognition process occurs due to the coordination of Hg2+ with ligands such as benzene rings, carboxyl groups, and pyridine N in three-dimensional space. Hg2+ was detected by measuring the ratio between two fluorescence peaks (I559 nm/I616 nm) within the range 2-20 μM, achieving a remarkably low detection limit of 40 nM. The established ratiometric fluorescence method has been successfully applied to the determination of Hg2+ in industrial wastewater of complex composition. The method plays a crucial role in the rapid and sensitive monitoring of Hg2+ in real environmental samples. The recoveries ranged from 92.82% to 112.67% (n = 3) with relative standard deviations (RSD) below 4.8%. This study offers a convenient and effective method for constructing probes for Hg2+ monitoring, with practical applications in environmental monitoring.

Europium Nanoparticle-Based Lateral Flow Strip Biosensors Combined with Recombinase Polymerase Amplification for Simultaneous Detection of Five Zoonotic Foodborne Pathogens

The five recognized zoonotic foodborne pathogens, namely, Listeria monocytogenes, Staphylococcus aureus, Streptococcus suis, Salmonella enterica and Escherichia coli O157:H7, pose a major threat to global health and social-economic development. These pathogenic bacteria can cause human and animal diseases through foodborne transmission and environmental contamination. Rapid and sensitive detection for pathogens is particularly important for the effective prevention of zoonotic infections. In this study, rapid and visual europium nanoparticle (EuNP)-based lateral flow strip biosensors (LFSBs) combined with recombinase polymerase amplification (RPA) were developed for the simultaneous quantitative detection of five foodborne pathogenic bacteria. Multiple T lines were designed in a single test strip for increasing the detection throughput. After optimizing the key parameters, the single-tube amplified reaction was completed within 15 min at 37 °C. The fluorescent strip reader recorded the intensity signals from the lateral flow strip and converted the data into a T/C value for quantification measurement. The sensitivity of the quintuple RPA-EuNP-LFSBs reached a level of 10¹ CFU/mL. It also exhibited good specificity and there was no cross-reaction with 20 non-target pathogens. In artificial contamination experiments, the recovery rate of the quintuple RPA-EuNP-LFSBs was 90.6-101.6%, and the results were consistent with those of the culture method. In summary, the ultrasensitive bacterial LFSBs described in this study have the potential for widespread application in resource-poor areas. The study also provides insights in respect to multiple detection in the field.

A MOF-on-MOF composite encapsulating sensitized Tb(III) as a built-in self-calibrating fluorescent platform for selective sensing of F ions

The establishment of simple and sensitive detection methods for fluoride ion (F^-) is of great importance for its effective prevention and control, and metal-organic framework (MOF) has attracted much attention for sensing applications due to its high surface areas and tunable structures. Herein, we successfully synthesized a fluorescent probe for ratiometric sensing of F^- by encapsulating sensitized Tb³⁺ in a MOF-on-MOF material (UIO66/MOF801, with the formula of C₄₈H₂₈O₃₂Zr₆ and C₂₄H₂O₃₂Zr₆, respectively). We found that Tb³⁺@UIO66/MOF801 can be used as a built-in fluorescent probe for fluorescence-enhanced sensing of F^-. Interestingly, the two fluorescence emission peaks of Tb³⁺@UIO66/MOF801 at 375 nm and 544 nm exhibit different fluorescence responses to F^- under excitation at 300 nm. The 544 nm peak is sensitive to F^-, while the 375 nm peak is insensitive to it. Photophysical analysis indicated that the photosensitive substance was formed, which promotes the absorption of 300 nm excitation light by the system. Self-calibrating fluorescent detection of F^- was achieved due to the unequal energy transfer toward the two different emission centers. The detection limit of Tb³⁺@UIO66/MOF801 for F^- was 4.029 μM, which is far lower than the WHO guideline for drinking water. Moreover, the ratiometric fluorescence strategy showed a high concentration tolerance of interference, because of its inner-reference effect. This work highlights the high potential of lanthanide ion encapsulated MOF-on-MOF as environmental sensors, and offers a scalable way for construction of the ratiometric fluorescence sensing systems.

Dye-sensitized lanthanide containing nanoparticles for luminescence based applications

Due to their exceptional luminescent properties, lanthanide (Ln) complexes represent a unique palette of probes in the spectroscopic toolkit. Their extremely weak brightness due to forbidden Ln electronic transitions can be overcome by indirect dye-sensitization from the antenna effect brought by organic ligands. Despite the improvement brought by the antenna effect, (bio)analytical applications with discrete Ln complexes as luminescent markers still suffers from low sensitivity as they are limited by the complex brightness. Thus, there is a need to develop nano-objects that cumulate the spectroscopic properties of multiple Ln ions. This review firstly gives a brief introduction of the spectral properties of lanthanides both in complexes and in nanoparticles (NPs). Then, the research progress of the design of Ln-doped inorganic NPs with capping antennas, Ln-complex encapsulated NPs and Ln-complex surface functionalized NPs is presented along with a summary of the various photosensitizing ligands and of the spectroscopic properties (excited-state lifetime, brightness, quantum yield). The review also emphasizes the problems and limitations encountered over the years and the solutions provided to address them. Finally, a comparison of the advantages and drawbacks of the three types of NP is provided as well as a conclusion about the remaining challenges both in the design of brighter NPs and in the luminescence based applications.

A "bottle-around-ship" method to encapsulated carbon nitride and CdTe quantum dots in ZIF-8 as the dual emission fluorescent probe for detection of mercury (II) ion

A facile and efficient "bottle-around-ship" approach for preparing the ratiometric fluorescent probe has been developed by encapsulating the red-colored fluorescence CdTe quantum dots (QDs) and blue-colored fluorescence graphitic carbon nitride quantum dots (g-CNQDs) into the zeolitic imidazolate metal-organic frameworks (ZIF-8) in one step. At a single excitation of 360 nm, the obtained probe ZIF-8@g-CNQD/CdTe shows the dual-emission peaked at 450 and 633 nm, respectively. The red emission of CdTe QDs is selectively quenched by the Hg²⁺, whereas the blue fluorescence of g-CNQDs as an internal reference is insensitive, resulting in an apparent color transformation from pink to blue for special recognition of Hg²⁺. By this approach, the relative fluorescence intensity ratio (F₆₃₃/F₄₅₀) decreased linearly with increasing Hg²⁺ concentration in the 0.2-3.5 μM range with a low limit of detection (LOD) of ~ 46 nM. Therefore, we demonstrate that this "bottle-around-ship" process provides a new strategy for the construction of ratiometric fluorescent Hg²⁺ probes with good simplicity, high efficiency, and excellent stabilities. Moreover, the obtained Hg²⁺ fluorescent probe shows good results in the detection of actual samples.

A cucurbit[6]uril based supramolecular assembly for the detection and removal of dyes and antibiotics from water

A cucurbit[6]uril (CB[6]) based supramolecular assembly CB[6]-[NDS]^2- (1, NDS = 2,6-naphthalenedisulfonic acid anion) was used to detect dyes such as reactive blue 19 (RB19), rhodamine B (RB), methyl orange (MO), methyl red (MR), and methyl violet (MV), and isoquinoline antibiotics such as berberine (BER) and palmatine (PAL) with detection limits of 143, 128, 374, 193, 305, 27 and 34 ppb, respectively. Simultaneously, 1 also displayed high adsorption abilities towards these organic molecules. These results indicate that 1 is a favorable material for the simultaneous selective detection and removal of specific dyes and antibiotics from water, being potentially useful in monitoring water quality and treating wastewater. The possible mechanisms of the detection and adsorption are also proposed.

Test-strip and smartphone-assisted Eu-TCPE-based ratiometric fluorescence sensor for the ultrasensitive detection of tetracycline

A dual-emissive Eu-TCPE-based test-strip sensor was developed for the ultrasensitive ratiometric and visual detection of tetracycline in real samples.

A cucurbit[7]uril-based supramolecular fluorescent probe for the detection of metronidazole with high sensitivity and strong anti-interference capacity

We propose a new method for the selective detection of the antibiotic metronidazole (MNZ) using CB[7]-JAT (cucurbit[7]uril = CB[7] and JAT = jatrorrhizine) as a fluorescent probe, which is based on the competitive reaction between MNZ and JAT for the occupancy of the CB[7] cavity. The proposed method gives a good calibration curve in the concentration range of 0.38–60 μM, and the limit of detection for MNZ is 65 ng mL−1 with those obtained by the standard curve method. Moreover, the proposed method was successfully applied for the determination of MNZ in liquid milk. Most importantly, due to the high binding affinity between CB[7] and MNZ, the proposed method shows great anti-interference capacity to accurately detect MNZ in the presence of other antibiotics.

A portable test strip based on fluorescent europium-based metal-organic framework for rapid and visual detection of tetracycline in food samples

Residual tetracycline (TC) in animal food caused by abuse of antibiotics leads to many chronic diseases in the human body. The development of a simple and on-site visualization method for TC detection is need of the hour. Herein, a fluorescent europium-based metal-organic framework (Eu-MOF) sensor for visual and rapid detection of TC was developed. Eu-MOF displays a red emission being excited at 260 nm. Upon exposure to TC, significant fluorescence quenching was observed due to the inner filter effect and photoinduced electron transfer. Moreover, the developed sensor was applied for the detection of TC in milk and beef samples with recoveries of 96.1% to 106.3%, respectively. More importantly, a portable test strip based on Eu-MOF was manufactured. It is a highly selective and sensitive portable device for TC detection. The results can be distinguished immediately by naked eyes, making it become an excellent choice to detect TC in real-time application.

Ultrastable cucurbit[6]uril-based multifunctional supramolecular assembly for efficient detection of nitroaromatic compounds and antibiotics

A cucurbit[6]uril-based supramolecular assembly was used for rapid and sensitive detection of nitroaromatic compounds and antibiotics through luminescence quenching.

Fluorescent Detection of Methyl Mercury in Aqueous Solution and Live Cells Using Fluorescent Probe and Micelle Systems

It is highly challenging to develop fast and sensitive fluorescent methods for monitoring organic mercury in purely aqueous solutions as well as live cells. Especially, selective fluorescent detection of methylmercury over inorganic mercury ions has not been reported. We developed a fast and sensitive fluorescent detection method for Hg²⁺ ions as well as methylmercury using an amino acid-based fluorescent probe (1) and SDS micelles. The fluorescent probe in SDS micelles detected sensitively and selectively Hg²⁺ ions and methylmercury among 16 metal ions in purely aqueous solution by the enhancement of the red emission at 575 nm, and the detection of methylmercury was completed within 1 min. The probe in SDS micelles with EDTA showed highly sensitive and selective turn on detection for methylmercury over Hg²⁺. The limit of detection was 9.1 nM for Hg²⁺ (1.8 ppb, R² = 0.989) and 206 nM for CH₃Hg⁺ (R² = 0.997). 1 rapidly penetrated live cells and detected intracellular Hg²⁺ ions as well as CH₃Hg⁺ by the enhancement of both red emissions and green emissions. Subsequent treatment of EDTA into the cell confirmed the selective detection of methylmercury in the cells. The present work indicated that the fluorescent probe with micelle systems provided a fast, sensitive, and selective detection method for monitoring inorganic mercury as well as methyl mercury.

Tetracycline Generated Red Luminescence Based on a Novel Lanthanide Functionalized Layered Double Hydroxide Nanoplatform

Considerable interest in using lanthanide complexes in optics have been well-known persisted for a long time. But such molecular-based edifices have been excluded from practical application because of their poor thermal or photo stabilities. Here a novel europium embedded layered double hydroxide (Mg-Al LDH-Eu) has been established and such an inorganic-organic framework demonstrates improved thermal performance due to hydrolysis and poly condensation of the trimethoxysilyl-unit. In addition, the incorporation of a functional building block such as ethylenediamine triacetic acid can significantly minimize the negative effects of hydroxyl groups. In the presence of tetracycline (Tc), the nanoprobe exhibits an "off-on" change in aqueous solution, and the red luminescence can be excited in the visible light range (405 nm). It provides a very sensitive signal response to Tc with an excellent linear relation in the range of 0.1 μM to 5.0 μM, and the detection limit of this probe is measured to be 7.6 nM. This nanoplatform exhibits low cytotoxicity during in vitro experiments and can be employed for the detection of tetracycline in 293T cells.

A novel and ultrasensitive yellow to taupe brown colorimetric sensing and removal method for Hg(ii) based on the thermosensitive poly(N-isopropyl acrylamide) stabilized silver nanoparticles

AgNP/PNIPAm was developed as a dual-functional colorimetric probe and removal system for Hg²⁺.

Time-resolved Fluorescent Detection for Glucose Using a Complex of Luminescent Layered Titanates and Enzymes

Luminescent europium-doped layered titanates (Eu-TiOx) were synthesized and complexed with horseradish peroxidase (HRP) and glucose oxidase (GOx). The emission of a resultant Eu-TiOx/HRP/GOx complex decreased upon the addition of glucose in the presence of guaiacol. The emission decrease was dependent on the concentrations of glucose, and the detection limit for glucose was 3.1 μM. The proposed system would be promising as a new detection method for glucose.

Boric-Acid-Functional Lanthanide Metal-Organic Frameworks for Selective Ratiometric Fluorescence Detection of Fluoride Ions

Here, we report that boric acid is used to tune the optical properties of lanthanide metal-organic frameworks (LMOFs) for dual-fluorescence emission and improves the selectivity of LMOFs for the determination of F^- ions. The LMOFs are prepared with 5-boronoisophthalic acid (5-bop) and Eu³⁺ ions as the precursors. Emission mechanism study indicates that 5-bop is excited with UV photons to produce its triplet state, which then excites Eu³⁺ ions for their red emission. This is the general story of the antenna effect, but electron-deficient boric acid decreases the energy transfer efficiency from the triplet state of 5-bop to Eu³⁺ ions, so dual emission from both 5-bop and Eu³⁺ ions is efficiently excited at the single excitation of 275 nm. Moreover, boric acid is used to identify fluoride specifically as a free accessible site. The ratiometric fluorescent detection of F^- ions is validated with the dual emission at single excitation. The LMOFs are very monodisperse, so the determination of aqueous F^- ions is easily achieved with high selectivity and a low detection limit (2 μM). For the first time, we reveal that rational selection of functional ligands can improve the sensing efficiency of LMOFs through tuning their optical property and enhancing the selectivity toward targets.

Simultaneous realization of Hg(2+) sensing, magnetic resonance imaging and upconversion luminescence in vitro and in vivo bioimaging based on hollow mesoporous silica coated UCNPs and ruthenium complex

We have constructed a multifunctional nanoprobe with sensing and imaging properties by using hollow mesoporous silica coated upconversion nanoparticles (UCNPs) and Hg(2+) responsive ruthenium (Ru) complex. The Ru complex was loaded into the hollow mesoporous silica and the UCNPs acted as an energy donor, transferring luminescence energy to the Ru complex. Furthermore, polyethylenimine (PEI) was assembled on the surface of mesoporous silica to achieve better hydrophilic and bio-compatibility. Upon addition of Hg(2+), a blue shift of the absorption peak of the Ru complex is observed and the energy transfer process between the UCNPs and the Ru complex was blocked, resulting in an increase of the green emission intensity of the UCNPs. The un-changed 801 nm emission of the nanoprobe was used as an internal standard reference and the detection limit of Hg(2+) was determined to be 0.16 μM for this nanoprobe in aqueous solution. In addition, based on the low cytotoxicity as studied by CCK-8 assay, the nanoprobe was successfully applied for cell imaging and small animal imaging. Furthermore, when doped with Gd(3+) ions, the nanoprobe was successfully applied to in vivo magnetic resonance imaging (MRI) of Kunming mice, which demonstrates its potential as a MRI positive-contrast agent. Therefore, the method and results may provide more exciting opportunities to afford nanoprobes with multimodal bioimaging and multifunctional applications.

High-throughput and rapid fluorescent visualization sensor of urinary citrate by CdTe quantum dots

In this paper, we have presented a novel CdTe quantum dots (QDs) based fluorescent sensor for visual and turn-on sensing of citrate in human urine samples. The europium ion (Eu(3+)) can lead to the fluorescence quenching of thioglycollic acid (TGA) modified CdTe QDs due to photoinduced electron transfer accompanied by the change of emission color from yellow to orange. Next, addition of citrate breaks the preformed assembly because citrate can replace the CdTe QDs, based on the fact that the Eu(3+) ion displays higher affinity with citrate than the CdTe QDs. Thus the photoinduced electron transfer is switched off, and the fluorescence emission of CdTe QDs is rapidly (within 5min) recovered, simultaneously, the orange emission color restores to yellow. Such proposed strategy may conveniently discriminate the patient of renal stone from normal person by naked eyes. In addition to visualization detection, the fluorescence responses can be used for well quantifying citrate in the range of 0.67-133μM. So, the present, simple, low-cost and visualized citrate fluorescence sensor has great potential in the applications for earlier screening in clinical detection.

Metal(ii)–organic frameworks with 3,3′-diphenyldicarboxylate and 1,3-bis(4-pyridyl)propane: preparation, crystal structures and luminescence

3D frameworks were constructed from Zn(ii)/Cd(ii)/Cu(ii), 3,3′-diphenyldicarboxylate, and 1,3-bis(4-pyridyl)propane. The Zn-framework was used as a fluorescent probe to sense benzaldehyde.

Highly sensitive SERS sensor for mercury ions based on the catalytic reaction of mercury ion decorated Ag nanoparticles

Schematic diagram of the SERS sensing mechanism for mercury ions by a catalytic oxidation reaction.