Rational Design of Dual-Emission Lanthanide Metal-Organic Framework for Visual Alkaline Phosphatase Activity Assay

Phage@lanthanide metal-organic framework-based fluorescent biosensor for smartphone-assisted simultaneous detection of multiple foodborne pathogens

The simple, rapid, and simultaneous detection of multiple foodborne pathogens in food is crucial for ensuring public safety. In this study, a rational design strategy for lanthanide-based metal-organic frameworks (Ln-MOFs), informed by theoretical calculations, was proposed. The calculated results were experimentally verified to screen out the optimal Ln-MOF for fluorescence efficiency. The selected Ln-MOFs were coupled with phages that exhibit specific pathogen recognition to develop phage@Ln-MOF fluorescent probes, while the magnetic nanoparticles were conjugated with phages to form capture probes. On this basis, a fluorescent biosensor was developed for the simultaneous detection of three major foodborne pathogens-Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Salmonella. This sensor facilitated the detection of all three pathogens within 15 min, with limit of detection (LOD) as low as 1 CFU/mL. Moreover, this fluorescent biosensor was compatible with on-site visual detection, utilizing a self-designed portable dark box and smartphone-assisted visualization, achieving an LOD of approximately 1-2 CFU/mL for E. coli, S. aureus, and Salmonella. This work demonstrates a novel approach for the rapid on-site detection of multiple foodborne pathogens, which holds promise for advancing field-ready diagnostic tools in food safety monitoring.

Customized Controllable Pyrophosphate Nanosensor Based on Lanthanide Metal-Organic Frameworks for Accurate and Sensitive Detection of Nucleic Acids

Pyrophosphate (PPi) and nucleic acid amplification play a critical role in medical diagnostics, making the development of precise nanosensors essential. Lanthanide metal-organic frameworks (Ln-MOFs) are increasingly recognized for their potential in advanced luminescent biosensing applications. However, research on customized controllable responses in Ln-MOF nanosensors is still lacking, which is critical for the molecular-level modular design. In this work, we introduce a ligand engineering strategy to regulate coordination-induced antenna effect emission in Ln-MOFs, optimizing their pyrophosphate (PPi) sensing from fluorescence turn-off to turn-on modes. By tuning the coordination environment through ligand programming, we discovered a "near coordination compensation" effect, allowing for controllable transitions between aggregation-induced emission and quenching (AIE/AIQ). This reversible response was supported by density functional theory calculations. Using a Eu3+/Tb3+ dual-emission Ln-MOF designed with 2,6-pyridinedicarboxylic acid as the optimized ligand, we developed a self-correcting PPi nanosensor with a detection limit of 0.2 μM. Moreover, this system enabled ultrasensitive nucleic acid detection, achieving a limit of detection (LOD) as low as 1 fM, with applications in DNA pyrosequencing, qPCR, and DNA epigenetic modification (5-formylcytosine) analysis. These findings shed light on the structural and photophysical factors controlling Ln-MOF luminescence, offering a promising platform for highly accurate and sensitive nucleic acid detection in biomedical diagnostics.

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.

A NbO-type mixed lanthanide metal-organic framework for cryogenic temperature sensing

A novel NbO-type Eu/Tb-mixed lanthanide metal-organic framework has been developed for the highly sensitive, self-calibrating detection of cryogenic temperature.

A nanomaterial-independent and fluorescent immunoassay based on Eu-micelles for rapid and sensitive detection of fluoroquinolones in chicken

Fluorescent nanoprobes are widely applied in innovate enzyme-linked immunosorbent assays (ELISA) for detection of fluoroquinolones (FQs) residue in foodstuffs. Nevertheless, the complicated synthesis of nanoprobes hampers their practical applications. Herein, a nanomaterial-independent and fluorescent ELISA for sensitive detection of FQs is developed using the Eu-micelles as signal probe. Non-nanostructured Eu-micelles with high quantum yield and stability are facilely synthesized through the assembly of Eu3+ and ligands. Alkaline phosphatase catalyzes hydrolysis of 4-nitrophenyl phosphate to 4-nitrophenol. The fluorescent Eu-micelles can be readily quenched by 4-nitrophenol via static quenching. The signal generation mechanism integrates well with conventional ELISA systems. The established fluorescent ELISA achieves sensitive detection of FQs with a limit of detection of 0.03 μg/kg. The validation results from LC-MS show that the fluorescent ELISA exhibits good accuracy and recoveries. Our study presents a nanomaterial-independent strategy for developing the rapid immunoassay for FQs, which holds good promise for practical applications.

Advances in metal-organic frameworks for optically selective alkaline phosphatase activity monitoring: a perspective

The study of Metal-Organic Frameworks (MOFs) has gained significant momentum due to their remarkable properties, including adjustable pore sizes, extensive surface area, and customizable compositions, which have urged scientists to investigate their applicability in pertinent societal issues such as water absorption, environmental remediation, and sensor technology. MOFs have the ability to transport and detect specific biomolecules, including proteins. One such biomolecule is alkaline phosphatase (ALP) that can be influenced by various diseases and can lead to severe consequences when its regulation is disrupted. The porous nature of MOFs and their tunable nature allows them to selectively adsorb, interact directly or indirectly with ALP. This ultimately influences the electronic and optical properties of the MOF, leading to measurable changes. Early detection and continuous monitoring of ALP play a crucial role in the use of an effective treatment, and recent studies have shown that MOFs are effective in detecting alkaline phosphatases. This manuscript offers a thorough examination of the potential biomedical applications of MOFs for monitoring alkaline phosphatase and envisions possible future trends in this field.

A Thermo-Responsive MOFs for X-Ray Scintillator

Thermo-responsive smart materials have aroused extensive interest due to the particular significance of temperature sensing. Although various photoluminescent materials are explored in thermal detection, it is not applicable enough in X-ray radiation environment where the accuracy and reliability will be influenced. Here, a strategy is proposed by introducing the concept of radio-luminescent functional building units (RBUs) to construct thermo-responsive lanthanide metal-organic frameworks (Ln-MOFs) scintillators for self-calibrating thermometry. The rational designs of RBUs (including organic ligand and Tb3+/Eu3+) with appropriate energy levels lead to high-performance radio-luminescence. Ln-MOFs scintillators exhibit perfect linear response to X-ray, presenting low dose rate detection limit (min ≈156.1 nGyairs-1). Self-calibrating detection based on ratiometric XEL intensities is achieved with good absolute and relative sensitivities of 6.74 and 8.1%K-1, respectively. High relative light yield (max ≈39000 photons MeV-1), imaging spatial resolution (max ≈18 lp mm-1), irradiation stability (intensity ≈100% at 368 K in total dose up to 215 Gyair), and giant color transformation visualization benefit the applications, especially the in situ thermo-responsive X-ray imaging. Such strategy provides a promising way to develop the novel smart photonic materials with excellent scintillator performances.

Enhancing Kinase Activity Detection with a Programmable Lanthanide Metal-Organic Framework via ATP-to-ADP Conversion

Precise modulation of host-guest interactions between programmable Ln-MOFs (lanthanide metal-organic frameworks) and phosphate analytes holds immense promise for enabling novel functionalities in biosensing. However, the intricate relationship between these functionalities and structures remains largely elusive. Understanding this correlation is crucial for advancing the rational design of fluorescent biosensor technology. Presently, there exists a large research gap concerning the utilization of Ln-MOFsto monitor the conversion of ATP to ADP, which poses a limitation for kinase detection. In this work, we delve into the potential of Ln-MOFs to amplify the fluorescence response during the kinase-mediated ATP-to-ADP conversion. Six Eu-MOFs were synthesized and Eu-TPTC ([1,1':4',1″]-terphenyl-3,3'',5,5''-tetracarboxylic acid) was selected as a ratiometric fluorescent probe, which is most suitable for high-precision detection of creatine kinase activity through the differential response from ATP to ADP. The molecular -level mechanism was confirmed by density functional theory. Furthermore, a simple paper chip-based platform was constructed to realize the fast (20 min) and sensitive (limit of detection is 0.34 U/L) creatine kinase activity detection in biological samples. Ln-MOF-phosphate interactions offer promising avenues for kinase activity assays and hold the potential for precise customization of analytical chemistry.

Multifunctional Lanthanide Metal-Organic Frameworks Are Used for Fluorescence Sensing of Bi3+, HPO42-, Flu, and PNBA and Application

Using a nitrogen-containing tricarboxylic acid ligand (imidazole-1-yl) benzene-2,4,6-tricarboxylic acid (H3ttc) and lanthanide metal elements (Dy, Eu, Nd, and Gd), four lanthanide metal organic frameworks (Ln-MOFs) with the same structure, namely, {[Dy2 (Httc)3]·1.5DMF}n(1), {[Eu2 (Httc)3]·1.5DMF}n(2), {[Nd2 (Httc)3]·1.5DMF}n(3), and {[Gd2 (Httc)3]·1.5DMF}n(4), were synthesized under solvothermal conditions. The characterization analysis showed that the four isomorphic Ln-MOFs were trigonal crystals of the R3̅c space group, with good phase purity and thermal stability. Fluorescence analysis showed that complex 1 can be an excellent fluorescence sensor for Bi3+, HPO42-, and fluridine (Flu), while complex 2 can be an excellent fluorescence sensor for p-nitrobenzoic acid (PNBA). And their sensing mechanisms were discussed in detail. The fluorescent test paper and fluorescent seal were prepared by using the excellent luminescence properties of 1 and 2, and the pesticide on the surface of cherry tomato was detected. The applicability of these MOFs as fluorescence sensors was proved. Therefore, Ln-MOFs are expected to have unpredictable application prospects in the field of environmental detection.

Ratiometric fluoroprobe based on Eu-MOF@Tb3+ for detecting tetracycline hydrochloride in freshwater fish and its application in rapid visual detection

Tetracycline hydrochloride (TCH), a prevalent antibiotic in aquaculture for treating bacterial infections, poses challenges for on-site detection. This study employed the reversed-phase microemulsion method to synthesize a uniform nano metal-organic framework (MOF) material, europium-benzene-p-dicarboxylic acid (Eu-BDC), doped with Tb3+ to form a dual-emission fluorescence probe. By leveraging the combined a-photoinduced electron-transfer (a-PET) and inner filter effect (IFE) mechanisms, high-sensitivity TCH detection in Carassius auratus and Ruditapes philippinarum was achieved. The detection range for TCH is 0.380-75 μM, with a low limit of detection (LOD) at 0.115 μM. Upon TCH binding, Eu-BDC fluorescence rapidly decreased, while Tb3+ fluorescence remained constant, establishing a ratiometric fluorescence change. Investigation into the TCH quenching mechanism on Eu-BDC was conducted using time-dependent density functional theory (TD-DFT) calculations and fluorescence quenching kinetic equations, suggesting a mixed quenching mechanism. Furthermore, a novel photoelectric conversion fluorescence detection device (FL-2) was developed and evaluated in conjunction with high-performance liquid chromatography-diode-array detection (HPLC-DAD). This is the first dedicated fluorescence device for TCH detection, showcasing superior photoelectric conversion performance and stability that reduces experimental errors associated with smartphone photography methods, presenting a promising avenue for on-site rapid TCH detection.

Rapid analysis of dichlorvos via releasing the phosphate core

Monitoring the residual dichlorvos (O,O-dimethyl-O-2,2-dichlorovinylphosphate, DDVP) in food has received extensive attention owing to its large consumption in agriculture. However, the previous sensing methods are not time-efficient enough due to the long incubation time for enzyme inhibition (tens of minutes to hours) or bottlenecked by the complicated procedures for senor fabrication. Herein, a novel sensing strategy is proposed based on the hydrolysis of DDVP into PO43-. By using alkaline phosphatase for hydrolysis, a certain portion of DDVP was transformed to PO43- within only 8 min. Then, the released PO43- was detected by a fluorescent terbium metal-organic framework (Tb-MOF). The coordination of the naked P-O groups to the metal nodes of the Tb-MOF disturbed the antenna effects of its ligands. Thus, DDVP was quantified by the decrease of the fluorescence of Tb ions. Based on this method, DDVP residues on plum surfaces were collected by swabs and successfully detected. The recovery of DDVP was determined in the range from 105 % to 115 %, demonstrating the quantification accuracy of this method. The detection limit reached 4.7 μM, which was lower than the restricted amount in fruit set by the National Standard of China. The present method provides an efficient and user-friendly way for the detection of DDVP and many other organophosphorus pesticides in food.

Design and application of dual-emission metal-organic framework-based ratiometric fluorescence sensors

Metal-organic frameworks (MOFs) are novel inorganic-organic hybridized crystals with a wide range of applications. In the last twenty years, fluorescence sensing based on MOFs has attracted much attention. MOFs can exhibit luminescence from metal nodes, ligands or introduced guests, which provides an excellent fluorescence response in sensing. However, single-signal emitting MOFs are susceptible to interference from concentration, environment, and excitation intensity, resulting in poor accuracy. To overcome the shortcomings, dual-emission MOF-based ratiometric fluorescence sensors have been proposed and rapidly developed. In this review, we first introduce the luminescence mechanisms, synthetic methods, and detection mechanisms of dual-emission MOFs, highlight the strategies for constructing ratiometric fluorescence sensors based on dual-emission MOFs, and classify them into three categories: intrinsic dual-emission and single-emission MOFs with luminescent guests, and non-emission MOFs with other luminescent materials. Then, we summarize the recent advances in dual-emission MOF-based ratiometric fluorescence sensors in various analytical industries. Finally, we discuss the current challenges and prospects for the future development of these sensors.

Amorphous amEu-NH2BDC and amTb-NH2BDC as ratio fluorescence probes for smartphone-integrated naked eye detection of bacillus anthracis biomarker

The abnormal concentration of anthrax spore biomarker 2,6-pyridinedicarboxylic acid (2,6-DPA) will seriously affect public health. Therefore, a sensitive and rapid assay for 2,6-DPA monitoring is of vital importance. In this work, novel nano-sized amorphous Eu-NH2BDC (amEu-NH2BDC) and amorphous Tb-NH2BDC (amTb-NH2BDC) metal organic frameworks are prepared by adjusting the ratio of metal and ligand, respectively. Both of them exhibit highly sensitive and selective ratiometric fluorescence detection for 2,6-DPA with wider linear range and lower detection limit in aqueous solutions and human serum. Attributed to the coordination effect of 2,6-DPA in triggering the characteristic fluorescence emissions of Eu3+or Tb3+ by replacing coordinated solvent molecules, as evidenced by ultraviolet-visible spectroscopy, the fluorescence lifetimes analysis, thermal gravimetric analysis, Fourier-transform infrared spectroscopy, density functional theory (DFT) simulations and X-ray photoelectron spectroscopy. In addition, the amEu-NH2BDC or amTb-NH2BDC loaded paper-based microsensors are constructed for real-time and sensitive detection of 2,6-DPA and coupled with a smartphone-assisted visual portable device.

The construction of dual-emissive ratiometric fluorescent probes based on fluorescent nanoparticles for the detection of metal ions and small molecules

With the rapid development of fluorescent nanoparticles (FNPs), such as CDs, QDs, and MOFs, the construction of FNP-based probes has played a key role in improving chemical sensors. Ratiometric fluorescent probes exhibit distinct advantages, such as resistance to environmental interference and achieving visualization. Thus, FNP-based dual-emission ratiometric fluorescent probes (DRFPs) have rapidly developed in the field of metal ion and small molecule detection in the past few years. In this review, firstly we introduce the fluorescence sensing mechanisms; then, we focus on the strategies for the fabrication of DRFPs, including hybrid FNPs, single FNPs with intrinsic dual emission and target-induced new emission, and DRFPs based on auxiliary nanoparticles. In the section on hybrid FNPs, methods to assemble two types of FNPs, such as chemical bonding, electrostatic interaction, core satellite or core-shell structures, coordination, and encapsulation, are introduced. In the section on single FNPs with intrinsic dual emission, methods for the design of dual-emission CDs, QDs, and MOFs are discussed. Regarding target-induced new emission, sensitization, coordination, hydrogen bonding, and chemical reaction induced new emissions are discussed. Furthermore, in the section on DRFPs based on auxiliary nanoparticles, auxiliary nanomaterials with the inner filter effect and enzyme mimicking activity are discussed. Finally, the existing challenges and an outlook on the future of DRFP are presented. We sincerely hope that this review will contribute to the quick understanding and exploration of DRFPs by researchers.

Nanoporous Crystalline Materials for the Recognition and Applications of Nucleic Acids

Nucleic acid plays a crucial role in countless biological processes. Hence, there is great interest in its detection and analysis in various fields from chemistry, biology, to medicine. Nanoporous crystalline materials exhibit enormous potential as an effective platform for nucleic acid recognition and application. These materials have highly ordered and uniform pore structures, as well as adjustable surface chemistry and pore size, making them good carriers for nucleic acid extraction, detection, and delivery. In this review, the latest developments in nanoporous crystalline materials, including metal organic frameworks (MOFs), covalent organic frameworks (COFs), and supramolecular organic frameworks (SOFs) for nucleic acid recognition and applications are discussed. Different strategies for functionalizing these materials are explored to specifically identify nucleic acid targets. Their applications in selective separation and detection of nucleic acids are highlighted. They can also be used as DNA/RNA sensors, gene delivery agents, host DNAzymes, and in DNA-based computing. Other applications include catalysis, data storage, and biomimetics. The development of novel nanoporous crystalline materials with enhanced biocompatibility has opened up new avenues in the fields of nucleic acid analysis and therapy, paving the way for the development of sensitive, selective, and cost-effective diagnostic and therapeutic tools with widespread applications.

Boric acid group-functional Tb-MOF as a fluorescent and captured probe for the highly sensitive and selective determination of propyl gallate in edible oils

This study reports the development of a Tb-metal-organic framework (Tb-MOF)-based fluorescent platform for the detection of propyl gallate (PG). The Tb-MOF using 5-boronoisophthalic acid (5-bop) as the ligand exhibited multiple emissions at 490, 543, 585, and 622 nm under an excitation wavelength of 256 nm. The fluorescence of Tb-MOF was selectively and significantly weakened in the presence of PG due to the special nucleophilic reaction between the boric acid of Tb-MOF and o-diphenol hydroxyl of PG, and the combined effect of static quenching and internal filtering. Furthermore, this sensor enabled the determination of PG within seconds in a wide linear range of 1-150 μg/mL, and with a low detection limit of 0.098 μg/mL, and high specificity against other phenolic antioxidants. This work provided a new route for the sensitive and selective determination of PG in soybean oil, thus was perspective to monitor and reduce the risk of PG overuse.

Controllable formation of polydopamine on carbon dots for ultrasensitive detection of alkaline phosphatase and ratiometric fluorescence immunoassay of benzocaine

Sensing alkaline phosphatase (ALP) activity with high sensitivity and accuracy is critical for both ALP-related health and food safety supervision and the development of ALP-triggered immunoassay platforms. Herein, an ultrasensitive ratiometric fluorescence (RF) sensing system based on the controllable formation of luminescent polydopamine and efficient quenching of carbon dots was proposed for the ALP activity assay, achieving quantitative detection in the range of 0.01-100 mU/L. Furthermore, this RF sensing system was integrated with an ALP-based ELISA platform to construct an RF-ELISA for benzocaine, a potentially abused anesthetic in edible fish, and ultrasensitive assay at the level of fg/mL was realized. This ratiometric strategy-based platform effectively shields various interferences through the self-calibration effect, thus providing more accurate and reliable quantification results. This study not only offers an efficient method for ultratrace detection of ALP and benzocaine but also proposes a universal platform for ultrasensitive detection of diverse targets in food analysis by replacing the recognition unit.

Dual-ligand two-dimensional terbium-organic frameworks nanosheets for ratiometric fluorescence detection of phosphate

Here, we reported a ratiometric fluorescence strategy for the detection of phosphate (Pi) in artificial wetland water. The strategy was based on dual-ligand two-dimensional terbium-organic frameworks nanosheets (2D Tb-NB MOFs). 2D Tb-NB MOFs were prepared through blending 5-boronoisophthalic acid (5-bop), 2-aminoterephthalic acid (NH₂-BDC) and Tb³⁺ ions at room temperature in the presence of triethylamine (TEA). The dual-ligand strategy realized dual emission originated from ligand NH₂-BDC and Tb³⁺ ions at 424 and 544 nm, respectively. Pi could compete with ligands to coordinate Tb³⁺ due to the strong binding ability between Pi and Tb³⁺, resulting in structural destruction of 2D Tb-NB MOFs, so static quenching and antenna effect between ligands and metal ions were interrupted, and emission at 424 nm was enhanced and emission at 544 nm was weakened. This novel probe had excellent linearity with Pi concentrations from 1 to 50 μmol/L; the detection limit was 0.16 μmol/L. This work revealed that mixed ligands improved sensing efficiency of MOFs by enhancing the sensitivity of the coordination between the analyte and MOFs.

Gelatinous lanthanide coordination polymer with aggregation-enhanced antenna effect for ratiometric detection of endogenous alkaline phosphatase

Aggregation-induced emission (AIE) and antenna effect (AE) are two significant behaviors that have attracted increasing attention. However, it is challenging to achieve the synergistic effect of AIE and AE in luminescent materials for more extensive applications. Here, four gelatinous Ln³⁺ coordination polymers (Ln-CPs) are synthesized by self-assembly of ciprofloxacin (CIP), adenosine monophosphate (AMP), and Ln³⁺ ions in aqueous medium. Encouragingly, a remarkable increase in the characteristic fluorescence of Ln³⁺ and a significant decrease in CIP are observed along with increasing concentration of Ln-CPs, which is attributed to the large aggregates formed by self-assembly that strictly constrain the intramolecular motions of antenna ligands, thereby achieving the aggregation-enhanced AE. More meaningfully, Eu-CP not only shows a rice-like morphology at high aggregation state, but also provides an opportunity for the selective detection of alkaline phosphatase (ALP). A new flower-like polymer is formed upon incubating Eu-CP with ALP, accompanied by the fluorescence quenching of Eu³⁺ and recovery of CIP, a ratiometric determination of ALP in the range of 0.1-6.0 U·L^-1 is thus achieved. Additionally, ALP assay in human serum and bioimaging in living cells have been successfully performed. This research opens a new horizon for the fabrication of Ln³⁺-based luminescent materials with promising applications.

Ratiometric singlet oxygen self-detecting and oxygen self-supplying nanosensor for real-time photodynamic therapy feedback and therapeutic effect enhancement

Integration of singlet oxygen (¹O₂) detection that provides necessary therapeutic feedback into nanotheranostics for hypoxic tumor photodynamic therapy (PDT) is desirable but still challenging. Herein, we report a nanosensor (denominated PAPD) by combining dual-channel ratiometric sensing and oxygen-augmenting strategies, which synergistically realizes real-time ¹O₂ self-detection, O₂ self-supply and enhanced phototherapy. PAPD nanosensor is constructed by encapsulating anthracene-based ¹O₂ sensitive fluorophore (DPA) into porphyrin metal-organic frameworks (PCN-224), decorating gold nanoparticles (AuNPs) as nanoenzymes, and coating polyethylene glycol thiol (PEG-SH) by the Au-S bond. PCN-224 serves as ¹O₂ reference fluorescence (FL) agent and photosensitizer. Once PCN-224-induced ¹O₂ is synthesized, the dual-channel ratiometric FL signal of PAPD actualizes sensitive, accurate and dynamic ¹O₂ visualization and gives real-time therapeutic information correlated with the therapeutic progression. Additionally, the catalase-like activity of PAPD possesses in situ O₂ production via intracellular H₂O₂ decomposition and accelerates ¹O₂ yields for amplifying the tumor cell killing efficiency. Moreover, the ratiometric ¹O₂ self-detection affords the capacity to evaluate the O₂ self-supplying effect in tumor 4T1 cells. Consequently, the rational-designed nanosensor PAPD provides a paradigm for real-time therapeutic evaluation and precise hypoxic tumor treatment clinically.

Supramolecular Photonic Hydrogel for High-Sensitivity Alkaline Phosphatase Detection via Synergistic Driving Force

Structurally-colored photonic hydrogels which are fabricated by introducing hydrogels into thin films or photonic crystal structures are promising candidates for biosensing. Generally, the design of photonic hydrogel biosensors is based on the sensor-analyte interactions induced charge variation within the hydrogel matrix, or chemically grafting binding sites onto the polymer chains, to achieve significant volume change and color variation of the photonic hydrogel. However, relatively low anti-interference capability or complicated synthesis hinder the facile and low-cost fabrication of high-performance photonic hydrogel biosensors. Here, a facilely prepared supramolecular photonic hydrogel biosensor is developed for high-sensitivity detection of alkaline phosphatase (ALP), which is an extensively considered clinical biomarker for a variety of diseases. Responding to ALP results in the broken supramolecular crosslinking and thus increased lattice distancing of the photonic hydrogel driven by synergistic repulsive force between nanoparticles embedded in photonic crystal structure and osmotic swelling pressure. The biosensor shows sensitivity of 7.3 nm spectral shift per mU mL^-1 ALP, with detection limit of 0.52 mU mL^-1 . High-accuracy colorimetric detection can be realized via a smartphone, promoting point-of-care sensing and timely diagnosis of related pathological conditions.

A Robust Ratiometric Fluorescent Sensor Based on Covalent Assembly of Dipeptides and Biomolecules for the High-Sensitive and Optosmart Detection of Pyrethroids

In this study, two ultrashort dipeptides, diphenylalanine (FF) or C-terminal amidated diphenylalanine (DPA), were covalently self-assembled with genipin to obtain two well-defined supramolecular peptide nanoparticles for the detection of pyrethroids. DPA-genipin nanoparticles (PNPs) demonstrated excellent dual-emission fluorescence characteristics, tunable particle size, and robust photostability. Parallel to this, PNPs showed a ratiometric fluorescence response to λ-cyhalothrin (LC) with a distinct green-to-red color transition. The satisfactory self-calibration capability of the ratiometric system enabled PNPs to respond sensitively to LC in a wide range (5-800 μg/L) with a lower limit of detection of 0.034 μg/L. The introduction of a smartphone application made it easy to develop an intelligent evaluation platform based on PNPs, which had been proven to be applicable for on-site visualization of LC in agricultural products. The platform proposed here may be a new application of peptide self-assembly in sensing, with both important food safety implications and great economic value.

Dual-ligand lanthanide metal-organic framework for ratiometric fluorescence detection of the anthrax biomarker dipicolinic acid

Dipicolinic acid (DPA) is a unique biomarker of Bacillus anthracis. Development of a simple, fast, sensitive and timely DPA detection method is of great importance and interest for preventing mass disease outbreaks and treatment of anthrax. In this work, a novel lanthanide-doped fluorescence probe was constructed by coordination of Eu³⁺ with bifunctional UiO-66-(COOH)₂-NH₂ MOFs materials for efficient monitoring DPA. UiO-66-(COOH)₂-NH₂ MOFs were prepared using Zr⁴⁺ as a metal node, 1,2,4,5-benzenetetracarboxylic acid (H₄BTC) and 2-aminoterephthalic acid (NH₂-BDC) as bridging ligand through a simple one-pot synthesis method. By virtue their abundant carboxyl groups, UiO-66-(COOH)₂-NH₂ can readily grasp Eu³⁺ to form UiO-66-(COOH)₂-NH₂/Eu with coordinated water molecules at Eu sites. Upon interaction with DPA molecules, the coordinated H₂O molecules were replaced by DPA molecules which transfer energy to Eu³⁺ in UiO-66-(COOH)₂-NH₂/Eu and sensitize Eu³⁺ luminescence. Meanwhile, DPA has a characteristic absorption band at 270 nm, which overlapped with the excitation spectrum of NH₂-BDC, allowing the fluorescence of UiO-66-(COOH)₂-NH₂/Eu at 453 nm to be greatly quenched by DPA through inner filter effect (IFE). Therefore, the rationally designed UiO-66-(COOH)₂-NH₂/Eu complex not only exhibits strong hydrophilicity and high dispersion, but also serves as ratiometric fluorescence sensing platform for monitoring DPA concentration. This sensing platform showed a satisfactory linear relationship from 0.2 μM to 40 μM with a limit of detection of 25.0 nM and a noticeable fluorescence color change from blue to red, holding a great promise in practical applications.

An Overview of the Design of Metal-Organic Frameworks-Based Fluorescent Chemosensors and Biosensors

Taking advantage of high porosity, large surface area, tunable nanostructures and ease of functionalization, metal-organic frameworks (MOFs) have been popularly applied in different fields, including adsorption and separation, heterogeneous catalysis, drug delivery, light harvesting, and chemical/biological sensing. The abundant active sites for specific recognition and adjustable optical and electrical characteristics allow for the design of various sensing platforms with MOFs as promising candidates. In this review, we systematically introduce the recent advancements of MOFs-based fluorescent chemosensors and biosensors, mainly focusing on the sensing mechanisms and analytes, including inorganic ions, small organic molecules and biomarkers (e.g., small biomolecules, nucleic acids, proteins, enzymes, and tumor cells). This review may provide valuable references for the development of novel MOFs-based sensing platforms to meet the requirements of environment monitoring and clinical diagnosis.

Recent Advancements in Developments of Novel Fluorescent Probes: In Cellulo Recognitions of Alkaline Phosphatases

Alkaline phosphatase (ALP) is one of the vital phospho-ester bond cleaving biocatalysts that has inevitable significance in cellular systems, viz., early-stage osteoblast differentiation, cell integrity in tissues, bone mineralization, cancer biomarker, liver dysfunction, cellular osmotic pressure, protein folding and many more. Variation from optimal levels of ALP in intra and extracellular fluids can cause severe diseases, including death. Due to these reasons, ALP is considered as a vital biomarker for various preclinical and medical diagnosis. Fluorescence image-based diagnosis is the most widely used method, owing to its simplicity, robustness, non-invasive properties and excellent spatio-temporal resolution (up to the nM/pM level), as compared to conventional analytical techniques, such as the electroanalytical method, nuclear magnetic resonance (NMR) and high-performance liquid chromatography (HPLC). Most of the reviews reported for ALP’s recognition in the literature scarcely explain the structurally related, photophysical and biophysical parameters; and the sub-cellular localizations. Considering these facts, in order to enhance the opto-analytical parameters of fluorescence-based diagnostic materials at the cellular level, herein we have systematically documented recent developments in the opto-analytical capabilities of quencher-free probes for ALP, used in in vitro (biological buffers) to in cellulo conditions, along with in vivo models.

Photoelectrochemical immunosensor for the sensitive detection of neuron-specific enolase based on the effect of Z-scheme WO3/NiCo2O4 nanoarrays p-n heterojunction

In this study, a signal-on type PEC immunosensor was constructed to detect neuron-specific enolase (NSE) via Z-scheme WO₃/NiCo₂O₄ p-n heterojunction with cactus-like structure used as photoactive materials and Mn_xCd_1-xS⊃Au NPs (MCS⊃Au NPs) as signal labels. Firstly, Z-scheme WO₃/NiCo₂O₄ heterojunction could accelerate the separation efficiency of carriers and well-matched photoactive materials may promote charge migration, which resulted in WO₃/NiCo₂O₄ generating strong and stable current. In addition, Z-scheme WO₃/NiCo₂O₄ heterojunction directly grown on the surface of FTO via hydrothermal method facilitated the preparation of PEC immunosensor with outstanding stability. Secondly, an efficient signal amplification strategy was proposed by Mn_xCd_1-xS⊃Au NPs incubating with signal antibody (Ab₂). On the one hand, the well-matched energy levels of Mn_xCd_1-xS with WO₃/NiCo₂O₄ boosted the photo-generated electrons transferred to the electrode; on the other hand, the LSPR effect of Au may convert thermion to photocurrent to achieve signal amplification. Based on the above strategies, a PEC immunosensor with outstanding reproducibility and stability was obtained for sensitive detection of NSE. Under the optimum experimental conditions, current response range of the constructed signal amplification PEC sensor to NSE was 0.1 pg/mL ∼50 ng/mL and the detection limit was 0.07 pg/mL (S/N = 3). After the application tests in the detection of actual samples, the feasibility of the prepared PEC immunosensor with excellent selectivity, high sensitivity and satisfactory reproducibility was verified and the satisfactory results were obtained.

Stable Lanthanide Metal-Organic Frameworks with Ratiometric Fluorescence Sensing for Amino Acids and Tunable Proton Conduction and Magnetic Properties

Four new isostructural lanthanide metal-organic frameworks (MOFs), namely {[Ln(DMTP-DC)_1.5(H₂O)₃]·DMF}_n [H₂DMTP-DC = 2',5'-dimethoxytriphenyl-4,4″-dicarboxylic acid; Ln^III = Eu^III (1), Gd^III (2), Tb^III (3), and Dy^III (4)], have been synthesized and characterized. Single-crystal structure analysis reveals that 1-4 are three-dimensional Ln-MOFs with rich H-bonding of coordinated H₂O molecules in the network channels. The X-ray diffraction patterns indicate that Ln-MOF 1 displays good stabilities in organic solvents and aqueous solutions with distinct pH values. Both 1 and 3 show characteristic emission of Ln^III ions. Ln-MOF 1 can be used as a ratiometric fluorescence sensor for arginine and lysine in aqueous solution, and the detection limits are 24.38 μM for arginine and 9.31 μM for lysine. All 1-4 show proton conductivity related to relative humidity (RH) and temperature, and the maximum conductivity values of 1-4 at 55 °C and 100% RH are 9.94 × 10^-5, 1.62 × 10^-4, 1.71 × 10^-4, and 2.67 × 10^-4 S·cm^-1, respectively. The value of σ increases with the decrease in ionic radius, indicating that the radius of the Ln^III ions can regulate the proton conductivity of these MOFs. Additionally, 2 exhibits a significant magnetocaloric effect (MCE) with a magnetic entropy change (-ΔS_m) of 18.86 J kg^-1 K^-1 for ΔH = 7 T at 2 K, and 4 shows weak field-induced slow relaxation of magnetization. The coexistence of good fluorescence sensing capability, attractive proton conductivity, and relatively large MCE in Ln-MOFs is rare, and thus, 1-4 are potentially multifunctional MOF materials.

Lanthanide-Organic Frameworks with Uncoordinated Lewis Base Sites: Tunable Luminescence, Antibiotic Detection, and Anticounterfeiting

Several new isostructural lanthanide metal-organic frameworks (Ln-MOFs), {[Ln₂(L)₃DMA₄]·2DMA}_n (1-Ln, where Ln = Eu, Tb, or Eu_xTb_1-x), were first constructed via the solvothermal reactions of 4,6-di(4-carboxyphenyl)pyrimidine and Ln³⁺ ions. 1-Ln exhibits a 4-connected two-dimensional framework endowed with uncoordinated Lewis base sites. An exploration of luminescence sensing demonstrated 1-Eu can be used for the selectivity detection of dimetridazole and metronidazole antibiotics in other antibiotics, blood plasma, and urine, acting as an exceptional recyclable luminescent probe. More importantly, the luminescent inks of 1-Ln are invisible, color adjustable, and stabilized, which may greatly improve their anticounterfeiting applications.

Multi-Emission from Single Metal-Organic Frameworks under Single Excitation

Multi-emission materials have come to prominent attention ascribed to their extended applications other than single-emission ones. General and robust design strategies of a single matrix with multi-emission under single excitation are urgently required. Metal-organic frameworks (MOFs) are porous materials prepared with organic ligands and metal nodes. The variety of metal nodes and ligands makes MOFs with great superiority as multi-emission matrices. Guest species encapsulated into the channels or pores of MOFs are the additional emission sites for multi-emission. In this review, multi-emission MOFs according to the different excitation sites are summarized and classified. The emission mechanisms are discussed, such as antenna effect, excited-state intramolecular proton transfer (ESIPT) and tautomerism for dual-emission. The factors that affect the emissions are revealed, including ligand-metal energy transfer and host-guest interaction, etc. Multi-emission MOFs could be predictably designed and prepared, once the emissive factors are controlled rationally in combination with the different multi-emission mechanisms. Correspondingly, new and practical applications are realized, including but not limited to ratiometric/multi-target sensing and bioimaging, white light-emitting diodes, and anti-counterfeiting. The design strategies of multi-emission MOFs and their extensive applications are reviewed. The results will shed light on other multi-emission systems to develop the structure-derived functionality and applications.

Carbon quantum dots with blue/near infrared emissions for ratiometric fluorescent lornoxicam sensing and bio-imaging

An economical and eco-friendly hydrothermal method for the preparation of nitrogen-doped carbon quantum dots (N-CQDs) was studied with rambutan peel and lysine. The morphology, structure, and optical properties of N-CQDs were characterized by transmission electron microscopy, Fourier transform infrared spectrometry, X-ray powder diffractometer, X-ray photoelectron spectrometry, and UV spectrophotometry. The synthesized N-CQDs have excellent characteristics such as strong fluorescence, good dispersion, high stability, and excellent water solubility. The absolute fluorescence quantum yield is 1.02%, the average particle size is 1.63 nm, and the maximum excitation wavelength is 340 nm. The maximum emission wavelengths are 430 nm and 800 nm. As a quencher, lornoxicam (LNX) was used to quench the fluorescence of N-CQDs with the mechanism of inner filter effect. The fluorescence ratio of N-CQDs (F430/F800) shows a good linear relationship to the concentration of LNX. The linear range and the detection limit of LNX are 0.01‒100 and 0.003 μmol/L, respectively. An effective ratiometric fluorescence probe for the detection of LNX was constructed. The method has the advantages of low detection limit, high sensitivity, wide linear range, and can be applied to the determination of LNX in real samples. Moreover, according to the excitation-dependent fluorescence behavior, dual-wavelength emission, and biocompatibility of N-CQDs, it has been applied to cell imaging.

Fluorescence detection of malachite green and cations (Cr3+, Fe3+ and Cu2+) by a europium-based coordination polymer

Due to remarkable fluorescence characteristics, lanthanide coordination polymers (CP) have been widely employed in fluorescence detection, but it is rarely reported that they act as multifunctional luminescent probes dedicated to detecting malachite green (MG) and various metal ions. A europium-based CP fluorescent probe, Eu(PDCA)2(H2O)6 (PDCA = 2,6-pyridinedicarboxylic acid), has been synthesized and exhibited excellent recognition ability for malachite green and metal cations (Cr3+, Fe3+ and Cu2+) among 11 metal cations, 13 anions and six other compounds. The recognition was achieved by fluorescence quenching when MG, Cr3+, Fe3+ and Cu2+ were added to a suspension of Eu(PDCA)2(H2O)6 respectively. Eu(PDCA)2(H2O)6 is a multifunctional luminescent probe, and displayed high quenching efficiencies K sv (2.10 × 106 M-1 for MG; 1.46 × 105 M-1 for Cr3+; 7.26 × 105 M-1 for Fe3+; 3.64 × 105 M-1 for Cu2+), and low detection limits (MG: 0.039 μM; Cr3+: 0.539 μM; Fe3+: 0.490 μM; Cu2+: 0.654 μM), presenting excellent selectivity and sensitivity, especially for MG. In addition, Eu(PDCA)2(H2O)6 was also made into fluorescent test strips, which can rapidly and effectively examine trace amounts of MG, Cr3+, Fe3+ and Cu2+ in aqueous solutions. This work provides a new perspective for detecting malachite green in fish ponds and heavy metal ions in waste water.

Folic acid functionalized molybdenum oxide quantum dots for the detection of Cu2+ ion and alkaline phosphatase via fluorescence turn off-on mechanism

The assay of alkaline phosphatase (ALP) plays a key role in the diagnosis of various diseases. Herein, folic acid functionalized molybdenum oxide quantum dots (FA-MoO_x QDs) are explored as fluorescence "turn- off and on" probes for assaying of Cu²⁺ ion and ALP, respectively. This fluorescence sensing strategy was based on the quenching of emission peak of FA-MoO_x QDs at 445 nm by Cu²⁺ ion, followed by restoring of emission peak selectively with ALP. Based on the quenching and restoring of FA-MoO_x QDs emission intensity, quantitative assay was developed for the detection of Cu²⁺ ion (0.20 - 500 µM) and ALP (0.06 - 150 U/L) with detection limits of 29 nM and 0.026 U/L, respectively. The developed FA-MoO_x QDs-based fluorescence "turn- off and on" strategy exhibited satisfactory results for assaying of ALP in biofluids.

Regulatory effects of miR-28 on osteogenic differentiation of human bone marrow mesenchymal stem cells

We aimed to assess the regulatory effects of miR-28 on the osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMMSCs). HBMMSCs isolated, cultured and induced (at P3) to undergo osteogenic induction. The expressions of miRNAs were detected by gene microarray, and differentially expressed miRNAs in hBMMSCs compared with induced cells were obtained by significance analysis of microarrays. The microarray findings were confirmed by RT-PCR. TargetScan showed that signal transducer and activator of transcription 1 (STAT1) was the downstream target gene of miR-28. The relationship between miR-28 and STAT1 was validated using dual-luciferase reporter gene assay. HBMMSCs were transfected with miR-28 mimics and STAT1 siRNA, respectively. Samples were collected on day 10 after osteogenic differentiation, and the alkaline phosphatase (AKP) activity, Runt-related transcription factor 2 (RUNX2, a key regulator of osteogenic differentiation) and STAT1 expressions were determined using kits, PCR and Western blotting, respectively. Cell proliferation and migration were detected through CCK-8 and Transwell assays, respectively. During the osteogenic differentiation of hBMMSCs, the expression level of miR-28 increased. MiR-28 specifically bound the 3'-untranslated region (3'UTR) of STAT1 mRNA. It inhibited STAT1 expression in a targeted manner during osteogenic differentiation. Interference with STAT1 partially mimicked the regulatory effects of miR-28 overexpression on the osteogenic differentiation of hBMMSCs. Interference with STAT1 or overexpression of miR-28 did not affect proliferation or migration. MiR-28 has gradually increased expression during the osteogenic differentiation of hBMMSCs, which can directly bind STAT1 3'UTR and inhibit its expression, thereby up-regulating AKP and RUNX2, and promoting osteogenic differentiation.

Homochiral porous coordination polymer of EuIII for metal ion sensing and enantioselective adsorption

A novel multifunctional homochiral porous metal–organic framework was obtained by combining the luminescent component Eu(iii) with an enantiopure triangular polycarboxylic ligand.

Dual-Functional Metal-Organic Framework for Luminescent Detection of Carcinoid Biomarkers and High Proton Conduction

It remains a challenge to exploit dual-functional metal-organic frameworks (MOFs) for applications, including luminescence detection and proton conduction. With the deliberate selection of the bifunctional organic ligand 5-sulfoisophthalic acid monosodium salt (NaH₂bts), and the phosphonic acid ligand N,N'-piperazine (bismethylenephosphonic acid; H₄L), a robust three-dimensional (3D) noninterpenetrating dual-functional MOF, [Tb(H₂L)(H₂bts)(H₂O)]·H₂O (1), has been synthesized hydrothermally. On the basis of the excellent thermal and chemical as well as superior luminescence stabilities in water and solutions with different pHs, 1 can serve as the simple, rapid, and highly selective and sensitive luminescence detection of the carcinoid biomarkers 5-hydroxytryptamine (HT) and its metabolite 5-hydroxyindole-3-acetic acid (HIAA) with detection limits of nanomolar magnitude in water and in simulated blood plasma and urine systems. Due to the change in the signals that could be readily differentiated by the naked eye under a UV lamp, a portable test paper has been developed. The probable quenching mechanisms are discussed in detail. In addition, a great number of hydrogen-bonding networks are formed among the uncoordinated carboxylic oxygen atoms, sulfonate oxygen atoms, protonated nitrogen atoms, and water molecules, which provide potential proton-hopping sites for proton conduction, leading to a maximum proton conductivity of 2.3 × 10^-4 S cm^-1 at 368 K and 95% relative humidity. The above results suggest that rationally designed dual-functional MOFs can open an avenue for the development of occupational diagnostic tools and alternative energy technology.

Multifunctional lanthanide metal-organic framework based ratiometric fluorescence visual detection platform for alkaline phosphatase activity

A turn-on/off ratiometric fluorescence detection platform based on multifunctional lanthanide metal-organic framework (Ln-MOF) and an enzymatic cascade reaction is proposed for alkaline phosphatase (ALP) activity assay. L-phosphotyrosine is hydrolyzed to levodopa (L-dopa) by two steps of enzymatic reaction. L-dopa further reacts with naphthoresorcinol to produce carboxyazamonardine with strong emission at 490 nm. In this process, multifunctional Ln-MOF (Cu@Eu-BTC, BTC is the 1,3,5-benzenetricarboxylic acid) acts not only as a nanozyme to catalyze the fluorogenic reaction between L-dopa and naphthoresorcinol but also as a fluorescence internal standard. The emission of Cu@Eu-BTC at 620 nm is quenched by phosphate anions, and the dual-response ratiometric fluorescence (F₄₉₀/F₆₂₀) can be achieved. A good linear relationship was obtained between Δ(F₄₉₀/F₆₂₀) and ALP activity in the range 0.3-24 U L^-1 with the detection limit of 0.02 U L^-1. In addition, a portable assay tube was designed for visual and point-of-care testing of ALP activity by color variation (ratiometric chromaticity). Both the ratiometric fluorescence detection and the visual detection methods were successfully applied to monitor ALP activity in human serum samples with recovery between 95.5%-109.0% and 94.0%-110.1%, and relative standard deviation less than 8.1% and 9.5%, respectively. As far as we know, this is the first report of ALP activity assay assisted by multifunctional Ln-MOF.Graphical abstract.