The Chemistry of Europium(III) Encountering DNA: Sprouting Unique Sequence-Dependent Performances for Multifunctional Time-Resolved Luminescent Assays

Fabrication of a two-dimensional bi-lanthanide metal-organic framework as a ratiometric fluorescent sensor based on energy competition

Bimetallic lanthanide metal-organic frameworks (bi-Ln-MOFs) exhibit great appeal for ratiometric luminescent sensors due to their unique advantages. Specially, the low-lying energy of the empty 4f band of Ce4+ ions benefits Ce-MOFs with robust and broad fluorescent emission. Therefore, constructing ratiometric sensors based on Ce-MOFs is of significance but remains a challenge. Here, a two-dimensional (2D) bi-Ln-MOF is fabricated using Eu3+/Ce4+ and 5-boronoisophthalic acid (5-bop) via a crystal phase transformation strategy to construct a ratiometric luminescent Hg2+ sensor. Due to the lower energy gap of Ce4+ compared to Eu3+ and the corresponding stronger energy-absorption ability, the Ce4+ in bi-Ln-MOF shows a stronger and broader fluorescent emission than that of Eu3+. The substitution of the boric acid group in the bi-Ln-MOF by Hg2+ amplifies the difference between the two lanthanide ions. Therefore, the fluorescence intensity of Ce4+ increases whereas that of Eu3+ decreases accordingly, a behavior distinct from individual Eu-MOF or Ce-MOF performance. This novel bi-Ln-MOF sensor not only achieves a wide linear response range from 0.5 to 120 μM with a low detection limit of 167 nM for Hg2+, but also demonstrates exceptional selectivity and stability. The intriguing sensing mechanism of energy competition and the novel synthesis approach for 2D bi-Ln-MOF are anticipated to broaden the application possibilities of bi-Ln-MOFs for designing ratiometric sensors.

The biological functions of europium-containing biomaterials: A systematic review

The biological functions of rare-earth elements (REEs) have become a focus of intense research. Recent studies have demonstrated that ion doping or alloying of some REEs can optimize the properties of traditional biomaterials. Europium (Eu), which is an REE with low toxicity and good biocompatibility, has promising applications in biomedicine. This article systematically reviews the osteogenic, angiogenic, neuritogenic, antibacterial, and anti-tumor properties of Eu-containing biomaterials, thereby paving the way for biomedical applications of Eu. Data collection for this review was completed in October 2022, and 30 relevant articles were finally included. Most articles indicated that doping of Eu ions or Eu-compound nanoparticles in biomaterials can improve their osteogenic, angiogenic, neuritogenic, antibacterial, and anti-tumor properties. The angiogenic, antibacterial, and potential neuritogenic effects of Eu(OH)₃ nanoparticles have also been demonstrated.

Recent Progress in Sensor Arrays: From Construction Principles of Sensing Elements to Applications

The traditional sensors are designed based on the "lock-and-key" strategy with high selectivity and specificity for detecting specific analytes, which however are not suitable for detecting multiple analytes simultaneously. With the help of pattern recognition technologies, the sensor arrays excel in distinguishing subtle changes caused by multitarget analytes with similar structures in a complex system. To construct a sensor array, the multiple sensing elements are undoubtedly indispensable units that will selectively interact with targets to generate the unique "fingerprints" based on the distinct responses, enabling the identification among various analytes through pattern recognition methods. This comprehensive review mainly focuses on the construction strategies and principles of sensing elements, as well as the applications of sensor array for identification and detection of target analytes in a wide range of fields. Furthermore, the present challenges and further perspectives of sensor arrays are discussed in detail.

An aptamer array for discriminating tetracycline antibiotics based on binding-enhanced intrinsic fluorescence

Tetracyclines are a class of antibiotics with a similar four-ringed structure. Due to this structural similarity, they are not easily differentiated from each other. We recently selected aptamers using oxytetracycline as a target and focused on an aptamer named OTC5, which has similar affinities for oxytetracycline (OTC), tetracycline (TC), and doxycycline (DOX). Tetracyclines exhibit an intrinsic fluorescence that is enhanced upon aptamer binding, allowing convenient binding assays and label-free detection. In this study, we analyzed the top 100 sequences from the previous selection library. Three other sequences were found to differentiate between different tetracyclines (OTC, DOX, and TC) by the selective enhancement of their intrinsic fluorescence. Among them, the OTC43 aptamer was more selective for OTC with a limit of detection (LOD) of 0.7 nM OTC, OTC22 was more selective for DOX (LOD 0.4 nM), and OTC2 was more selective for TC (0.3 nM). Using these three aptamers to form a sensor array, principal component analysis was able to discriminate between the three tetracyclines from each other and from the other molecules. This group of aptamers could be useful as probes for the detection of tetracycline antibiotics.

Luminescent Lanthanide Probes for Inorganic and Organic Phosphates

Inorganic and organic phosphates-including orthophosphate, nucleotides, and DNA-are some of the most fundamental anions in cellular biology, regulating numerous processes of both medical and environmental significance. The characteristic long lifetimes of emitting lanthanides, including the brighter europium(III) and terbium(III), make them ideally suited for the development of molecular probes for the detection of phosphates directly in complex aqueous media. Moreover, given their high oxophilicity and the exquisite sensitivity of their quantum yields to their hydration number, those luminescent lanthanides are perfect for the detection of phosphates. Herein we discuss the principles that have guided the recent developments of molecular probes selective for inorganic or organic phosphates and how these lanthanide complexes facilitate the study of numerous biological processes.

Time-Resolved Luminescent Sensing and Imaging for Enzyme Catalytic Activity Based on Responsive Probes

Enzymes, as a kind of biomacromolecules, play an important role in many physiological processes and relate directly to various diseases. Developing an efficient detection method for enzyme activity is important to achieve early diagnosis of enzyme-relevant diseases and high throughput screening of potential enzyme-relevant drugs. Time-resolved luminescence assay provide a high accuracy and signal-to-noise ratios detection methods for enzyme activity, which has been widely used in high throughput screening of enzyme-relevant drugs and diagnosis of enzyme-relevant diseases. Inspired by these advantages, various responsive probes based on metal complexes and metal-free organic compounds have been developed for time-resolved bioimaging and biosensing of enzyme activity owing to their long luminescence lifetimes, high quantum yields and photostability. In this review, we comprehensively reviewed metal complex- and metal-free organic compound-based responsive probes applied to detect enzyme activity through time-resolved imaging, including their design strategies and sensing principles. Current challenges and future prospects in this rapidly growing field are also discussed.

Radioactive waste treatments by using zeolites. A short review

Radionuclides in the environment is an important issue, many techniques have been developed for the removal of radionuclides from the environment. One of those techniques is the adsorption and natural and synthesized materials have been used to remove different radionuclides from water. The adsorbents used for removal of radionuclides should have high retention capacity and they should be resistant to radiation. One of the natural materials used is the zeolites due to its high ion exchange capacities, adsorption efficiency, resistance to radiation and abundance. The present review describes the advances made on radioactive waste treatments using zeolites as adsorbents, the elements: cesium, strontium, cobalt, molybdenum, uranium, plutonium, americium, samarium, and europium were selected according to their nuclear importance and their presence in the environment. Firstly, a brief description of the zeolites is given and then a review on the separation of these radionuclides from water by using zeolites is presented.

Metal-organic framework/3,3',5,5'-tetramethylbenzidine based multidimensional spectral array platform for sensitive discrimination of protein phosphorylation

A multifunctional metal-organic framework (MOF) hybrid Zr-FeTCPP-MOF is fabricated with 2-aminoterephthalic acid (NH₂-BDC) and Fe (III) meso-Tetra (4-carboxyphenyl) porphine chloride (FeTCPPCl) participating in the coordination to Zr₆ clusters via one-pot hydrothermal method. The adsorption of phosphoproteins on the surface of Zr-FeTCPP-MOF hybrid cause the chances on the absorbance (Abs), fluorescence (FL) and resonance light scattering (RLS) signals of Zr-FeTCPP-MOF/3,3',5,5'-Tetramethylbenzidine (TMB) system, and an array sensing platform is successfully built for sensitive identification of protein phosphorylation based on the three-dimensional spectral changes of MOF/TMB sensing system induced by the variations on the structure, size, and phosphorylation site of phosphoproteins. This array sensing system is robust in recognizing different phosphoprotein species, and shows high sensitivity in discriminating similar phosphoproteins of different phosphorylation distribution, i.e., caseins (α-, β- and κ-cas). The detection limit of this array sensing platform to individual phosphoprotein is low down to 5 nM. The practical application of this MOF/TMB-base sensing system is substantially demonstrated by identifying tau peptides with different phosphorylation distribution, and distinguishing cancer cells of abnormal phosphorylations from normal cells. This work proves the reliability, sensitivity, and practicality of the MOF/TMB-base sensing system platform for the diagnosis of phosphorylation-related diseases in clinical trials.

A single-component yet multifunctional tongue-mimicking sensor array for upconversion fluorescence biosensing

A novel single-component nanoprobe has been created for the pattern recognition of antioxidants in a “turn on” manner by integrating with the prevention of PDA formation with an antioxidant.

Direct Determination of Redox Statuses in Biological Thiols and Disulfides with Noncovalent Interactions of Poly(ionic liquid)s

The three most important redox couples, including cysteine (Cys)/cystine (Cyss), homocysteine (Hcys)/homocystine (Hcyss), and reduced glutathione (GSH)/glutathione disulfide (GSSG), are closely associated with human aging and many diseases. Thus, it is highly important to determine their redox statuses at the following two levels: (i) the redox identity in different thiols/disulfides and (ii) the redox ratio in a mixture of a specific couple. Herein, by using one single AIE-doped (AIE, aggregation-induced emission) photonic-structured poly(ionic liquid) (PIL) sphere as a virtual sensor array, we realize a direct determination of the redox status without a reducing pretreatment of disulfides, which will greatly promote the development of high-throughput and simple procedures. The pattern-recognition method uses the multiple noncovalent interactions of imidazolium-based PILs with these redox species to produce differential responses in both the photonic crystal and fluorescence dual channels. On the one hand, a single sphere enables the direct and simultaneous discrimination of the redox identities of Cys, Cyss, Hcys, Hcyss, GSH, and GSSG under the interference of other five commonly occurring thiols. On the other hand, this sphere also allows for not only a direct quantification of the GSH/GSSG ratios without previously determining the individual concentrations of GSH and GSSG but also the accurate prediction of the ratios in unknown redox samples. To further demonstrate applications of this method, redox mixtures in a biological sample are differentiated. Additionally, quantum calculations further support our assignments for interactions between the imidazolium-based PILs and these redox species.

Coordination polymers of Tb3+/Nucleotide as smart chemical nose/tongue toward pattern-recognition-based and time-resolved fluorescence sensing

The abundant functional groups on guanosine monophosphate (GMP) make it possible to interact with various metal ions. The subtle difference in the structure of GMP and deoxy-guanosine monophosphate (dGMP) coupled with Tb3+ can be readily exploited to form two coordination polymers, which have been unveiled as two time-resolved fluorescence (TRF) sensing reporters (Tb-GMP and Tb-dGMP) in our study. Based on this finding, herein, we have proposed a novel TRF orthogonal sensing array (Tb-GMP/dGMP) for pattern-recognition-based sensing of various metal ions. In addition, upon integration of some thiol-affinity metal ions, Tb-GMP/dGMP can be further extended to construct two metal ion-involved pattern-recognition-based sensor arrays (Tb-GMP/dGMP-Cu, Tb-GMP/dGMP-Ag) for the TRF sensing different levels of disease-relevant biothiols in biofluids, illustrating the powerful and multifunctional capabilities of the Tb-GMP/dGMP system and would inspire simpler and more widespread designs of chemical nose/tongue-based applications.

A ratiometric fluorescence platform based on boric-acid-functional Eu-MOF for sensitive detection of H2O2 and glucose

A Eu-metal organic framework (Eu-MOF) probe with dual-emission was reported for the ratiometric fluorescence detection of H₂O₂ and glucose. Because of the special nucleophilic reaction between boric group and H₂O₂, Eu³⁺ and 5-boronobenzene-1,3-dicarboxylic acid (BBDC) were selected to synthesize the functional MOF probe via a simple one-pot solvothermal method. The Eu-MOF shows dual-emission at 370 and 623 nm with the single excitation at 270 nm due to the energy transfer efficiency change for antenna effect procedure. After addition of H₂O₂, the red emission of Eu-MOF weakened and the blue emission enhances immediately under 270 nm irradiation, so the ratiometric fluorescence detection is established. Moreover, the obvious color change for visual measuring of H₂O₂ and glucose is illustrated to reveal the merit of Eu-MOF probe. The proposed method was demonstrated to be highly sensitive and selective for H₂O₂ and glucose, with the low detection limits of 0.0335 and 0.0643 μM, respectively. The established boric-acid-functional Eu-MOF sensing platform was proved as the powerful probe for H₂O₂ and the metabolites involved in H₂O₂-generating reaction.

Label-free non-invasive fluorescent pattern discrimination of thiols and chiral recognition of cysteine enantiomers in biofluids using a bioinspired copolymer-Cu2+ hybrid sensor array regulated by pH

Thiols play a crucial role in various biological processes, and the discrimination of thiols in biofluids is a significant but difficult issue. Herein, a facile label-free non-invasive fluorescent sensor array has been presented based on PDA/PEI_n-Cu²⁺ in three different pH buffer solutions for pattern discrimination of thiols and chiral recognition of cysteine (Cys) enantiomers in biofluids toward health monitoring. The proposed sensor array was fabricated based on the fact that Cu²⁺ has a strong affinity toward thiols, which prevents Cu²⁺ from binding PDA/PEI_n, and the fluorescence properties of PDA/PEI_n were recovered to a certain degree. Different thiols exhibited different affinities toward Cu²⁺, generating distinct fluorescence response patterns. These response patterns are characteristic for each thiol and can be discriminated by principal component analysis (PCA). In this work, three types of PDA/PEI₄₈-Cu²⁺ sensors (PDA/PEI₄₈-Cu₄ ²⁺, PDA/PEI₄₈-Cu_4.5 ²⁺ and PDA/PEI₄₈-Cu₅ ²⁺) were prepared by using acetate buffer with different pHs (at 4, 4.5, and 5) to form our proposed sensor array, which could realize the pattern discrimination of 8 thiols. Moreover, we successfully realized the sensitivity and selectivity assays to these thiols. Furthermore, the proposed sensor array could discriminate mixtures of thiols as well as the chiral recognition of mixtures of Cys enantiomers, promising its potential practical usage. Significantly, the resultant practical application in real samples showed that it could be a fascinating assay for the development of non-invasive diagnosis. This method promises the facile, sensitive and powerful discrimination of thiols in biofluids and would sprout more relevant strategies toward a broad range of applications.