Ultrasensitive and Selective Detection of Uranium by a Luminescent Terbium-Organic Framework

An ultrasensitive D-A fluorescent probe for dual-mode uranyl detection in environmental and biological systems

Given the escalating environmental risks posed by radioactive uranium contamination, there is an urgent demand for rapid and precise assessment of uranium levels in environmental and biological matrices. In this study, an ultrasensitive donor-acceptor fluorescent probe, TPA-BH, was developed for on-site rapid detection of uranium in both environmental samples and living systems. Owing to the synergistic effects of aggregation-induced emission (AIE), twisted intramolecular charge transfer (TICT) and specific coordination reactions, the probe achieved exceptional sensing performance: an ultra-low detection limit (0.0417 ppb, 720-fold below the WHO drinking water threshold), ultra-fast response (<1 min), and large Stokes shift (140 nm) with excellent selectivity across wide pH ranges (2-10). The probe demonstrated remarkable anti-interference capability in complex matrices while maintaining low cytotoxicity, enabling its successful application in real water analysis and live-cell imaging. Systematic investigations including photophysical characterization, real sample analysis, and recognition mechanism studies confirm the probe's potential for early warning of uranium pollution and public health risk assessment.

Green synthesis of fluorescent carbon dots embedded in silanized cellulose nanofibers: A ensitive and ustainable platform for uranium detection and remediation

The rise of uranium ions in groundwater in Northern India has raised serious health concerns, including increased cancer cases. This study introduces a novel solution using a hydrothermal method to synthesize highly fluorescent and stable carbon dots (CDs) from Kalanchoe pinnata. These CDs were embedded in silanized cellulose nanofibers (SCNFs) to create an eco-friendly dual-functional adsorbent and fluorescent probe (SCNFs@CDs) for the remediation of UO22+ ions. Characterization confirmed the successful integration of CDs, preserving the nanofibrous structure necessary for stability and recovery. SCNFs@CDs demonstrated a strong affinity for UO22+ ions, even amid competing ions, evidenced by a linear decline in the fluorescence intensity at 360 nm when increasing the concentration, achieving a low limit of detection of 1.64 nM. Adsorption investigation demonstrated pseudo-second order with a maximal adsorption capacity of 196.07 mg g-1, signifying chemisorption. Remarkably, SCNFs@CDs maintained 87 % adsorption efficiency after five cycles of use. Our findings underscore the potential of SCNFs@CDs as an effective, and sustainable solution which can be used both for UO22+ ions sensing and adsorption from aqueous media, contributing to eco-friendly water purification technologies.

Metal-organic frameworks as advanced platforms for radionuclide detection

The development of nuclear energy has significantly increased the prevalence of artificial radionuclides, mainly generated through nuclear fission processes, alongside naturally occurring radionuclides. These radionuclides, encompassing a wide array of elements, including 3H, 85Kr, 90Sr, 99Tc, 129/131I, 137Cs, 222Rn, 232Th, and 235/238U, exist in diverse chemical forms such as gases, ions, and molecular species, posing substantial risks to human health and environmental safety. Consequently, the precise detection and selective separation of these radionuclides are of paramount importance for the timely identification and mitigation of associated hazards. This review explores the application of metal-organic frameworks (MOFs) as advanced platforms for radionuclide detection, utilizing their structural tunability and versatile functionality. The discussion is systematically organized based on the chemical forms of radionuclides, categorizing them into gaseous, cationic, and anionic species. Key detection mechanisms employed by MOFs, including fluorescence sensing (via quenching, enhancement, and fluorochromism), scintillation techniques, colorimetric sensing, electrochemical sensing, and so on, are thoroughly examined. These approaches are analysed to elucidate their principles, practical implementations, and limitations.

Biplane Ion-Pairing Induced Supramolecular Assembly for High-Performance Uranium Detection

It is still challenging to directly recognize the anionic species [UO2(CO3)3]4-, the dominant species in the environment (82%-93%), using current optical probes because of the adverse effects of its thick hydration shell on binding interactions. In this study, a water-soluble Pt(II) methylated terpyridine complex ([Pt(CH3-tpy)NCO]+) supramolecular probe is designed to directly target [UO2(CO3)3]4- by a new strategy of thick hydration shell overlapping arrangement. The optical response demonstrates excellent selectivity among ≈30 investigated interfering substances, along with rapid response (≈15 s), high sensitivity (64.1 nm) and dual-signals. It is confirmed both experimentally and theoretically that the superior detection performance is attributed to the formation of a unique supramolecular structure featuring biplane-like building block, bicolumnar stacking and water-bridged anionic networks, via the overlap of thick hydration shells of aligned [UO2(CO3)3]4- to boost a superentropic driving force, and the distinguishable dual-signals arises from the emergence of four types of Pt-Pt interactions, generating low-energy metal-to-metal charge transfer adsorption/emission. In addition, a [Pt(CH3-tpy)NCO]+-based hydrogel platform is constructed for detecting both anionic and cationic uranium, with a detection limit of 14.89 fg. This work unlocks not only a way to directly detect [UO2(CO3)3]4-, but also a new idea for sensing ions with extreme thick hydration layers.

Highly Sensitive and Selective Detection of Uranyl Ions Based on a Tb3+-Functionalized MOF via Competitive Host-Guest Coordination

Owing to the rapid development of the nuclear industry, uranium has become a global environmental contaminant due to its radiotoxicity and chemotoxicity, posing significant threats to human health and ecological safety. Although various instrumental and chemical analytical methods have been developed for uranyl ion detection in aquatic environments, searching for new sensors with high stability, sensitivity, and selectivity remains a challenge. In this study, a luminescent Zr-based metal-organic framework (MOF), designated as Tb@UiO-66-(COOH)2, was successfully synthesized utilizing a postsynthetic exchange (PSE) method along with Tb3+ ion doping for uranyl ion detection. Interestingly, the presence of UO22+ ions causes a replacement of guest ions (Tb3+) in the sensor via a competitive host-guest interaction, leading to significant luminescence quenching. The attenuation of the luminescence intensity of Tb@UiO-66-(COOH)2 exhibits an excellent linear relationship with UO22+ ion concentrations within a wide range of 0-2.52 μM. Notably, Tb@UiO-66-(COOH)2 demonstrates an unprecedentedly high detection sensitivity (Ksv = 2.16 × 105 M-1) and an extremely low limit of detection (LOD) down to 8.03 nM (1.91 ppb) in deionized water. More importantly, Tb@UiO-66-(COOH)2 can achieve high selectivity and efficient detection performance, even in the presence of significant excesses of competing ions. The values of Ksv were determined to be 2.10 × 105 M-1 in Xie'ao Lake water and 3.05 × 105 M-1 in seawater; the values of LOD were determined to be 8.26 nM (1.96 ppb) in Xie'ao Lake water and 5.68 nM (1.35 ppb) in seawater. To the best of our knowledge, this is the first instance of introducing a competitive host-guest coordination strategy into a MOF-based chemical sensor to achieve high-performance uranyl ion detection. Hence, the present work offers a novel idea for building functional MOFs for uranyl ion detection in aqueous solutions.

Highly sensitive and specific uranyl ion detection by a fluorescent sensor containing uranyl-specific recognition sites

Uranium pollution has become a serious threat to human health and environmental safety, making the detection of environmental uranium contamination of great importance. The sensitive and specific detection of uranyl ions, which are the dominant form of uranium in the environment, depends on the specific recognition of uranyl ions by chemical groups. In this study, a novel fluorescent sensor containing a highly specific uranyl ion recognition group is synthesized via the reaction of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and 1,1,2,2-tetra(4-carboxylphenyl)ethylene (TPE-(COOH)4). Owing to the effects of aggregation-induced emission (AIE) and intramolecular charge transfer (ICT), the fluorescent sensor, named TPE-EDC, exhibits significant fluorescent properties in aqueous environments. The binding of uranyl ions by specific recognition groups in TPE-EDC leads to a decrease in the ICT effect, thus causing a significant reduction in the emission intensity of TPE-EDC. The attenuation of the fluorescence intensity of TPE-EDC shows an excellent linear relationship with an increase in uranyl ion concentration. TPE-EDC exhibits ultra-sensitive and ultra-selective detection ability for uranyl ions with an ultra-low detection limit of 69 pmol/L and an ultrashort response time of 30 s. These high detection performances render the fluorescent sensor TPE-EDC a promising candidate for early warning of uranium pollution.

Mechanistical Insights into the Ultrasensitive Detection of Radioactive and Chemotoxic UO22+ Ions by a Porous Anionic Co-Metal-Organic Framework

Development of a simple, cost-efficient, and portable UO22+ sensory probe with high selectivity and sensitivity is highly desirable in the context of monitoring radioactive contaminants. Herein, we report a luminescent Co-based metal-organic framework (MOF), {[Me2NH2]0.5[Co(DATRz)0.5(NH2BDC)]·xG}n (1), equipped with abundant amino functionalities for the selective detection of uranyl cations. The ionic structure consists of two types of channels decorated with plentiful Lewis basic amino moieties, which trigger a stronger acid-base interaction with the diffused cationic units and thus can selectively quench the fluorescence intensity in the presence of other interfering ions. Furthermore, the limit of detection for selective UO22+ sensing was achieved to be as low as 0.13 μM (30.94 ppb) with rapid responsiveness and multiple recyclabilities, demonstrating its excellent efficacy. Density functional theory (DFT) calculations further unraveled the preferred binding sites of the UO22+ ions in the tubular channel of the MOF structure. Orbital hybridization between NH2BDC/DATRz and UO22+ together with its significantly large electron-accepting ability is identified as responsible for the luminescence quenching. More importantly, the prepared 1@PVDF {poly(vinylidene difluoride)} mixed-matrix membrane (MMM) displayed good fluorescence activity comparable to 1, which is of great significance for their practical employment as MOF-based luminosensors in real-world sensing application.

Advanced "turn-on" colorimetric uranium platform based on the enhanced nanozyme activity of a donor-acceptor structured covalent organic framework

BACKGROUND

The increasing uranium containing wastes generated during uranium mining and finishing pose a huge threat to the environment and human health, and thus robust strategies for on-site monitoring of uranium pollutant are of great significance for environmental protection around uranium tailings.

RESULTS

Herein, a facile "turn-on" colorimetric platform that can achieve uranium detection by spectrometry and naked eyes was developed based on the uranium-enhanced nanozyme activity of covalent organic framework (JUC-505). Thanks to the extended π-conjugated skeleton and donor-acceptor (D-A) structure, JUC-505 exhibited superior photo-activated nanozyme activity, which would be prohibited when the cyano group in JUC-505 skeleton was transformed to the amidoxime group. Further results elucidated that the coordination of uranium with amidoxime groups led to the electron transfer between uranium and the JUC-505-AO skeleton, and thus significantly restored the nanozymatic activity of JUC-505-AO with the subsequent remarkable color changes. Moreover, the uranium concentrations in uranium tailing wastewater detected by the present "turn-on" colorimetric method were well agreed with those by ICP-MS, demonstrating a high accuracy of the present method in real samples.

SIGNIFICANCE

The D-A structured JUC-505 with superior photocatalytic property and nanozymatic activity was applied to facilitate colorimetric detection of uranium, which displays the advantages of low detection limit, excellent selectivity, fast response and simple operation for uranium detection in real samples, and shows a great potential in on-site monitoring of uranium pollutant around uranium tailings as well as nuclear power plant.

Dual-Color Visual Ratiometric Fluorescence Sensing for H2O and D2O Mixtures Using a Hexanuclear Ln(III) Cluster-Based Metal-Organic Framework

High-purity heavy water (D2O) is a strategic material owing to its important application in the fields of nuclear energy and scientific research. D2O always tends to get contaminated by H2O owing to its strong hygroscopicity. Herein, a bimetallic hexanuclear Ln(III) cluster-based metal-organic framework (Eu0.5Tb0.5-TZB-MOF) has been synthesized for fluorescence sensing of the D2O-H2O binary mixtures. Eu0.5Tb0.5-TZB-MOF can be used to immediately differentiate D2O or H2O via fluorescent color responses that are obvious to the naked eye and allow for quantitative ratiometric analysis using simple spectrophotometry. Fluorescence titration experiments demonstrate that both trace H2O in D2O and trace D2O in H2O can be quantitatively detected. Mechanistic studies demonstrate that the weaker vibrational quenching of the O-D oscillator compared to the O-H oscillator, in addition to the terbium-to-europium energy transfer, triggered the fluorescence signal response.

pH-Dependent Dual-Mode Detection toward Uranium by a Zinc-Tetraphenylethylene Fluorescent Metal-Organic Framework

An interpenetrated tetraphenylethylene-based fluorescent metal-organic framework (ECUT-180) with exceptional sensitivity, excellent selectivity, and fast response (less than 30 s) toward uranium was successfully prepared. Especially, in the prescence of uranyl, ECUT-180 displays significant fluorescence turn-on under pH 2-3, while fluorescence turn-off under pH 4-8. The corresponding detection limits were determined to be 2.92 ppb at pH 2 and 0.86 ppb at pH 8, both of which are lower than the average uranium content (3.3 ppb) in seawater. Mechanism investigation reveals that the fluorescence enhancement on the strong acid condition can be assigned to uranium adsorption, while the quenching is caused by the resonance energy transfer.

Recent advancement in nanomaterials for the detection and removal of uranium: A review

Uranyl ions U(VI), are the common by-product of nuclear power plants and anthropogenic activities like mining, excess utilization of fertilizers, oil industries, etc. Its intake into the body causes serious health concerns such as liver toxicity, brain damage, DNA damage and reproductive issues. Therefore, there is urgent need to develop the detection and remediation strategies. Nanomaterials (NMs), due to their unique physiochemical properties including very high specific area, tiny sizes, quantum effects, high chemical reactivity and selectivity have become emerging materials for the detection and remediation of these radioactive wastes. Therefore, the current study aims to provide a holistic view and investigation of these new emerging NMs that are effective for the detection and removal of Uranium including metal nanoparticles, carbon-based NMs, nanosized metal oxides, metal sulfides, metal-organic frameworks, cellulose NMs, metal carbides/nitrides, and carbon dots (CDs). Along with this, the production status, and its contamination data in food, water, and soil samples all across the world are also complied in this work.

The Fabrication and Mechanism of a Crystalline Organic Fluorescent Probe Based on Photoinduced Electron Transfer

The response performances of the crystalline organic fluorescence probe are highly dependent on the long-range ordered arrangement of crystalline structure. Herein, a novel organic crystalline fluorescent probe with a high quantum yield was established through the rapid self-assembly of 1,2,4,5-Tetrakis (4-carboxyphenyl) benzene (H4TCPB) and DMF molecules. Each H4TCPB, which connects to four DMF molecules through hydrogen bonds, acts as the structural unit. The building units are packed by π-π, lone pair···π, and lone pair···lone pair interactions to form solid-state crystalline materials. H4TCPB·4DMF exhibits distinct blue fluorescent under UV light, while the quantum yield is as high as 89.02% and the fluorescence lifetime is 1.95 ns. The H4TCPB·4DMF nanocrystal exhibits a specific fluorescence quench sensibility to tetracycline (TC), compared with the common chemicals and ions in environmental water. Moreover, the test results can be obtained quickly and are easily visible to the naked eye. The limit of detection for TC is as low as 12 nM in an aqueous solution. Spectral analysis and density functional theory (DFT) theoretical calculations were used to explain the fluorescence quenching mechanism of H4TCPB·4DMF toward TC, which could be attributed to the photoinduced electron transfer occurring from H4TCPB·4DMF to TC. Our work enriches the database of crystalline luminescent materials and provides theoretical support for the design and mechanical studies of organic fluorescent probes.

Synthesis of a Cd-MOF Fluorescence Sensor and Its Detection of Fe3+, Fluazinam, TNP, and Sulfasalazine Enteric-Coated Tablets in Aqueous Solution

A Cd-based metal-organic framework (Cd-MOF), named after {[Cd(ttc)(H₂O)]·H₂O}_n (ttc = 1-imidazole-1-yl-2,4,6-benzene-tricarboxylic acid), was synthesized using the solvothermal reaction. The single-crystal structure was determined by single X-ray diffraction analysis, and crystalline characteristics and composition were confirmed by powder X-ray diffraction (PXRD) and thermogravimetric analysis (TG), respectively. Structural analysis showed that the Cd²⁺ ion is in the seven-coordinated mode, in which ttc^2- ion adopts the μ₄-η¹-η¹-η²-η² coordination mode. It is worth noting that the Cd²⁺ ion is connected to ttc^2- to form a 2D network, and the adjacent 2D network is expanded into a 3D supramolecular network structure through weak hydrogen bonds. The fluorescence sensing experiments indicated that Cd-MOF could not only be used as a fluorescence sensor for Fe³⁺, fluazinam (FLU), and 2,4,6-trinitrophenolol (TNP) but also for sulfasalazine detection in aqueous solution. To verify the sensitivity of the fluorescent probe, we calculated its detection limit: 5.34 × 10^-8 M (Fe³⁺), 7.8 × 10^-8 M (FLU), 1.21 × 10^-7 M (TNP), and 2.67 × 10^-7 M (SECT). In addition, the quenching mechanism was thoroughly studied.

"Two-in-one" dual-function luminescent MOF hydrogel for onsite ultra-sensitive detection and efficient enrichment of radioactive uranium in water

In consideration of the severe hazards of radioactive uranium pollution and the growing demand of uranium resources, the novel sensor/adsorbent composite was creatively developed to integrate the dual functions for on-site detection of uranium contamination and efficient recovery of uranium resources. By hybridizing the luminescent 3D terbium (III) metal-organic framework (Tb-MOF) with sodium alginate (SA) gel using terbium (III) as cross-linker, the Tb-MOF/Tb-AG was fabricated with multi-luminescence centers and sufficient binding sites for uranium. Notably, the ultra-high sensitivity with detection limit as low as 1.2 ppt was achieved, which was 4 orders of magnitude lower than the uranium contamination standard in drinking water (USEPA) and even comparable to the sensitivity of the ICP-MS. Furthermore, the very wide quantification range (1.0 ×10^-9-5.0 ×10^-4 mol/L), remarkable adsorption capacity (549.0 mg/g) and outstanding anti-interference ability have been achieved without sophisticated sample preparation procedures. Applied in complex natural water samples from Uranium Tailings and the Pearl River, this method has shown good detection accuracy. The ultra high sensitivity and great adsorption capacity for uranium could be ascribed to the synergistic coordination, hydrogen bonding and ion exchange between uranium and Tb-MOF/Tb-AG. The mechanisms were explored by infrared spectroscopy, batch experiments, X-ray photoelectron studies and energy dispersive spectroscopic studies. In addition, the Tb-MOF/Tb-AG can be reused for uranium adsorption.

Simultaneous detection and separation of uranium based on a fluorescent amidoxime-functionalized covalent organic polymer

To ensure the long-term sustainable development of nuclear energy as well as the prevention and control of uranium pollution, new materials that can simultaneously detect and separate uranium are still urgently needed. Herein, a new fluorescent covalent organic polymer (COP), namely HT-COP-AO, was synthesized andemployed as both the fluorescent probe and absorbent for simultaneous uranium detection and separationconsidering its excellent fluorescence property and strong uranium coordination ability. The results showed that the fluorescence of HT-COP-AO was quickly quenched by uranium within 2 min, and the limit of detection was 0.23 µM (3σ/K). Further studies implied that uranium was coordinated with the amidoxime groups of HT-COP-AO through U-N and O = U = O bonds, which resulted in electron transfer from uranium to HT-COP-AO and quenching the fluorescence of HT-COP-AO consequently. Meanwhile, HT-COP-AO exhibited excellent absorption ability towards uranium, and the maximum absorption capacity (q_max = 401.3 mg/g) was higher than most reported amidoxime modified materials. The HT-COP-AO also showed high selectivity for both uranium detection and separation which makes it a great promising for uranium monitoring in real water samples.

Mn3O4@polyaniline nanocomposite with multiple active sites to capture uranium(VI) and iodide: synthesis, performance, and mechanism

A major challenge for radioactive wastewater treatment and associated environmental remediation is how to simultaneously remove cationic and anionic radionuclides. Herein, a series of Mn₃O₄@polyaniline (Mn₃O₄@PANI) nanocomposites were successfully prepared and used to remove U(VI) and I^- from aqueous solution, two highly concomitant species in nuclear pollution settings. Batch adsorption experiments reveal that the component Mn₃O₄ is predominantly responsible for U(VI) removal, but PANI for I^-. The nanocomposite with 24.2 wt% Mn₃O₄ possesses high removal percentages (> 85%) either for U(VI) or I^- over a wide pH range, fast removal kinetics, and excellent adsorption selectivity at high concentrations of competing ions. Benefiting from the contributions of the two components and the high adsorption affinities, the nanocomposite achieves the simultaneous removal to coexisting U(VI) and I^-, with a maximum adsorption capacity 102.6 mg/g for U(VI) and 126.1 mg/g for I^-. X-ray photoelectron spectroscopy (XPS) results reveal that the U(VI) adsorption occurs via coordination bonding with Mn-O, -NH- , and =N- groups in the nanocomposite, whereas I^- adsorption proceeds mainly through I anionic species exchange with Cl^- and interactions with π-bonds in PANI, as well as the electrostatic attraction onto Mn₃O₄. Considering the excellent performance and multiple active sites, the Mn₃O₄@PANI nanocomposite is promising to remove practical radioactive U(VI) and I^-.

Constructing an ultrastable imidazole covalent organic framework for concurrent uranium detection and recovery

Uranium is one of the most important strategic resources for the development of the nuclear industry, but its unintended release has created potential environmental and health risks. It is highly desired to explore new methods that enable concurrent uranium monitoring and recovery for environmental protection and sustainable development of the nuclear industry. Here, for the first time, an imidazole fluorescent covalent organic framework (named PyTT-Tp) with ultrastable skeleton and open nanopore channel is synthesized by condensing ammonium acetate, 1,3,5-triformylphloroglucinol and pyrene-4,5,9,10-tetrone. By precisely tailoring complexing ligands, PyTT-Tp shows an excellent uranium recovery capacity of 941.27 mg g^-1 and reached equilibrium within 60 min, which can be attributed to dense selective uranium binding sites on the highly accessible open skeleton. In addition, due to the signal amplification of the pyrene-imidazole skeleton, it has an ultra-low detection limit of 4.92 nM UO₂²⁺ and an ultra-fast response time (2 s) suitable for on-site monitoring the uranium content of the extracted water. By modulating target complexing ligands, this approach can be extended to the monitoring and recovery of other strategic nuclides.

Precise Design and Deliberate Tuning of Turn-On Fluorescence in Tetraphenylpyrazine-Based Metal−Organic Frameworks

The manipulation on turn-on fluorescence in solid state materials attracts increasing interests owing to their widespread applications. Herein we report how the nonradiative pathways of tetraphenylpyrazine (TPP) units in metal−organic frameworks (MOFs) systems could be hindered through a topological design approach. Two MOFs single crystals of different topology were constructed via the solvothermal reaction of a TPP-based 4,4′,4^″,4^‴-(pyrazine-2,3,5,6-tetrayl) tetrabenzoic acid (H₄TCPP) ligand and metal cations, and their mechanisms of formation have been explored. Compared with the innate low-frequency vibrational modes of flu net Tb-TCPP-1, such as phenyl ring torsions and pyrazine twists, Tb-TCPP-2 adopts a shp net, so the dihedral angle of pyrazine ring and phenyl arms is larger, and the center pyrazine ring in TPP unit is coplanar, which hinders the radiationless decay of TPP moieties in Tb-TCPP-2. Thereby Tb-TCPP-2 exhibits a larger blue-shifted fluorescence and a higher fluorescence quantum yield than Tb-TCPP-1, which is consistent with the reduced nonradiative pathways. Furthermore, Density functional theory (DFT) studies also confirmed aforementioned tunable turn-on fluorescence mechanism. Our work constructed TPP-type MOFs based on a deliberately topological design approach, and the precise design of turn-on fluorescence holds promise as a strategy for controlling nonradiative pathways.

Insertion of Hemin into Metal-Organic Frameworks: Mimicking Natural Peroxidase Microenvironment for the Rapid Ultrasensitive Detection of Uranium

Constructing enzyme-like active sites in mimic enzyme systems is critical for achieving catalytic performances comparable to natural enzymes and can shed light on the natural development of enzymes. In this study, we described a specific hemin-based mimetic enzyme, which was facilely synthesized by the assembly of zeolitic imidazolate framework-l (ZIF-l) and hemin. The obtained hemin-based mimetic enzyme (denoted as ZIF-l-hemin) displayed enhanced peroxidase activity compared to free hemin in solution. Such excellent activity originated from the ZIF-l framework mimicking the active site cavity microenvironment of horseradish peroxidase in terms of axially coordinated histidine and distal histidine. Additionally, the constructed peroxidase mimetic was extremely resistant to a variety of severe circumstances that would normally denature natural enzymes. These characteristics made ZIF-l-hemin a potential platform for the colorimetric sensor of uranium (UO₂²⁺) with wide linear ranges (0.25-40 μM) and low limits of detection (0.079 μM). Moreover, the detection mechanism demonstrated that the coordination of uranyl ion with imidazole of ZIF-l-hemin reduced the catalytic efficiency of ZIF-l-hemin. The current work not only proposed a novel approach for fabricating artificial peroxidase but also offered facile colorimetric methods for selective radionuclide detection.

Hydrolytically Stable Zr-Based Metal-Organic Framework as a Highly Sensitive and Selective Luminescent Sensor of Radionuclides

Effective detections of radionuclides including uranium and its predominant fission products, for example, iodine, are highly desired owing to their radiotoxicity and potential threat to human health. However, traditional analytical techniques of radionuclides are instrument-demanding, and chemosensors targeted for sensitization of radionuclides remain limited. In this regard, we report a sensitive and selective sensor of UO₂²⁺ and I^- based on the unique quenching behavior of a luminescent Zr-based metal-organic framework, Zr₆O₄(OH)₄(OH)₆(H₂O)₆(TCPE)_1.5·(H₂O)₂₄(C₃H₇NO)₉ (Zr-TCPE). Immobilization of the luminescent tetrakis(4-carboxyphenyl)ethylene (TCPE^4-) linkers by Zr₆ nodes enhances the photoluminescence quantum yield of Zr-TCPE, which facilitates the effective sensing of radionuclides in a "turn-off" manner. Moreover, Zr-TCPE can sensitively and selectively recognize UO₂²⁺ and I^- ions with the lowest limits of detection of 0.67 and 0.87 μg/kg, respectively, of which the former one is much lower than the permissible value (30 μg/L) defined by the U.S. EPA. In addition, Zr-TCPE features excellent hydrolytic stability and can withstand pH conditions ranging from 3 to 11. To facilitate real-world applications, we have further fabricated polyvinylidene fluoride-integrating Zr-TCPE as luminescence-based sensor membranes for on-site sensing of UO₂²⁺ and I^-.

A multifunctional basic pH indicator probe for distinguishable detection of Co2+, Cu2+ and Zn2+ with its utility in mitotracking and monitoring cytoplasmic viscosity in apoptotic cells

Metal ions such as Co²⁺, Cu²⁺ and Zn²⁺ have extensive applications in biological and industrial realms, but the toxicity caused by these ions poses a serious threat to mankind. However, there is no report in the literature on the development of a chemosensor for distinguishable detection of these toxic ions. Addressing this challenge, a multifunctional probe as a basic pH indicator with both colorimetric and fluorescence turn-on responses has been reported. The probe selectively discriminates Co²⁺, Cu²⁺ and Zn²⁺ ions with brown, dark yellow and greenish yellow colors, respectively, in DMF : water (9 : 1 v/v, HEPES 10 mM). Additionally, a fluorescence turn-on response specific to Zn²⁺ has also been observed. The sensing mechanism has been explored using UV-Vis, fluorescence spectroscopy and ¹H NMR titration and confirmed with computational results. The inhibition of CN isomerization and excited state intramolecular proton transfer (ESIPT) along with chelation enhanced fluorescence emission (CHEF) result in fluorescence enhancement with Zn²⁺. Job's plot and HRMS spectra confirm a 1 : 1 (L : M) stoichiometry between the probe and metal ions. The probe is able to exhibit excellent viscochromism in DMF : glycerol medium. Live cell imaging on SiHa cells has been successfully performed for intra-cellular detection of Zn²⁺ at basic pH. Furthermore, the probe displays its utility in mitotracking and monitoring cytoplasmic viscosity changes in SiHa cells. It is efficiently used to recognize the apoptosis process by displaying an enhancement in fluorescence intensity from cancerous SiHa cells to apoptotic cells.

Monosystem Discriminative Sensor toward Inorganic Anions via Incorporating Three Different Luminescent Channels in Metal-Organic Frameworks

Because there are great demands of distinguishing multiple chemically similar analytes, chemical sensors for multivariate analyses have been developed rapidly in the past few decades. However, designing luminescent discriminative sensors based on a monosystem has been a challenge until now. In this work, we first develop a triemitting luminescent discriminative platform named RGB@TLU-2 with three different emission centers: blue-emitting center (BDC-NH₂), green-emitting (Tb@BDC-SO₃^-), and red-emitting center (rhodamine B, RhB). The different luminescent mechanisms (ligand emission, LMET emission, guest emission) in these emission centers endow RGB@TLU-2 with high cross-reactivity, which is essential for discriminating applications. To balance the three luminescent centers, all variables in the synthesis process are optimized carefully. Surprisingly, the RGB@TLU-2 shows a variety of luminescent response patterns when immersed into 12 inorganic anions. Two unsupervised multidimensional analysis methods, (principal component analysis and hierarchical cluster analysis), are used to explore the relationship between these anions. On the basis of the luminescent response of analytes, 5 response modes are obtained and 12 inorganic anions are classified into 6 groups. The sensing mechanisms are discussed in detail. Detection limits of typical anions Cr₂O₇^2-, PO₄^3-, ClO^-, and NO₂^- are calculated as 2.895 × 10^-8, 6.353 × 10^-6, 1.134 × 10^-5, and 4.56 × 10^-4 mol/L, respectively. Furthermore, the RGB@TLU-2 also shows the ability to distinguish 4 (Fe³⁺, Fe²⁺, Cu²⁺ and Cr³⁺) of 12 metal ions and 3 (Trp, Pro, and Arg) of 11 amino acids.