Detection of Purine Metabolite Uric Acid with Picolinic-Acid-Functionalized Metal-Organic Frameworks

Manganese Silicate with Proximity Effect and Enhanced Polarity toward Substrates for Efficient Enzymatic Biosensing

Functional nanoparticle-mediated enzymatic sensors have been extensively utilized in the colorimetric detection of biomolecules. However, low affinity toward substrates and unstable color development of oxidized substrates severely influence the detection period and reliability of results. Herein, a rapid and reliable method has been proposed by employing manganese silicate NPs (MSs) as the paradigm for enzymatic colorimetric detection of uric acid (UA). MSs demonstrate favorable catalytic kinetics (Km = 0.046 mM). Compared with reported methods, the shortened detection period and ultralong enzymatic curve platform (∼8 min) ensure higher rapidity and reliability. Theoretical calculations based on density functional theory were further utilized to reveal the catalytic mechanism of the MSs oxidase mimic. The inherent ability to spontaneously generate ROS along with its proximity effect resulting from substrate adsorption provides robust theoretical support for ultrafast catalytic kinetics. Moreover, silicate ions reduced the degree of electron delocalization in oxidized TMB with increasing molecular polarity and decreased the solvation free energy to further improve the dissolution stability. As expected, the MSs-based method exhibits excellent accuracy and higher stability in monitoring UA change of human urine specimens, which is superior to the commercial kit. Furthermore, the integration of colorimetric methodologies with portable smart detection systems bridges fundamental scientific exploration and practical implementation, enabling both a reduced detection cost and expanded applicability of nanozyme-based sensors.

Multifunctional Cd(II) Metal-Organic Framework with Abundant Lewis Acidic and Basic Sites: Selective Gas Adsorption and Separation, CO2 Catalytic Fixation, and Fluorescence Recognition of Uric Acid

The development of new porous materials for the selective adsorption and fixation of CO2, as well as the selective capture of C2H2, is essential for environmental protection and energy security. Herein, a versatile coordination polymer, {[Cd(btbpa)(H2O)]·3H2O·4NMP·DMA}n (Cd-btbpa, H2btbpa = 4,4'-bis(1H-1,2,4-triazole-1-yl)-[1,1'-biphenyl]-3,3'-dicarboxylic acid), has been prepared, which not only exhibits good chemical and thermal stability but also possesses adaptive nanochannels. Gas uptake studies disclosed the selective adsorption properties of MOF Cd-btbpa for CO2 and C2H2 over other gases (N2, CH4, C2H4, and C2H6), contributing to a record-high IAST selectivity of ca. 3905 (50/50 of CO2/CH4, v/v). The adsorption selectivity values for C2H2/C2H4 and CO2/N2 at 298 K are 2.14 and 41.79, respectively. Breakthrough experiments were carried out to confirm its practical application value for CO2/CH4, CO2/N2, and C2H2/C2H4 separation. In addition, it can drive heterogeneous cycloaddition of CO2 with various epoxides under mild conditions (75 °C, 1 atm) and boost the yield of produced cyclic carbonates almost to 100% for the epoxides such as 1,2-epoxybutane and epichlorohydrin. Besides, Cd-btbpa shows excellent recognition ability for uric acid (UA) with high KSV (3.9378 × 104 M-1) and sensitivity (LOD: 0.14 μM).

Wood membrane: A sustainable electrochemical platform for enzyme-free and pretreatment-free monitoring uric acid in bodily fluids

The detection of biomarkers is crucial for assessing disease status and progression. Uric acid (UA), a common biomarker in body fluids, plays an important role in the diagnosis and monitoring of conditions such as hyperuricemia, chronic kidney disease, and cardiovascular disease. However, the low concentration of UA in non-invasive body fluids, combined with numerous interfering substances, makes its detection challenging. Therefore, there is a pressing need to develop advanced sensor platforms that exhibit both high sensitivity and excellent specificity for accurate monitoring of UA levels in various body fluids. In this study, an electrochemical sensing system is developed by integrating a cascade interference-removal zone and a target-response zone on a wooden channel membrane (CM) for the pretreatment-free detection of UA in body fluids. In this design, cysteine-doped ZIF-67(Co) nanocrystals, a mimic with multi-enzyme activity, are modified in the interference-removal zone. The target-response zone on the other side of the CM is contacted with a solution containing Fe3+ and [Fe(CN)6]3- ions. Using saliva as a proof-of-concept, the interference species, including ascorbic acid (AA), dopamine (DA), and glutathione (GSH), are oxidized and removed when passing through the interference-removal zone, while UA reaches the target-response zone and triggers the growth of Prussian blue (PB) on site. Utilizing the peroxidase-like activity of PB, UA concentration is directly determined based on changes in transmembrane ion currents. The resulting sensing system exhibits higher sensitivity than commercial UA meters and demonstrates straightforward, continuous, and non-invasive monitoring of UA in saliva after consuming purine-rich foods. The technology provides a simple, reliable and low-cost device for sensing UA in complex biological matrices. Moreover, the CM based sensing device also provides the benefit of being incineratable and biodegradable, reducing medical and electronic waste, making it eco-friendly for daily diagnostics.

In situ fabricated gold nanostars on hydrogel beads as photo-oxidase mimics for rapid and sustainable POCT of uric acid

Synthetic enzyme mimics surpass their natural counterparts in terms of stability, efficiency, and cost-effectiveness, making them highly valuable for catalytic applications. Gold nanomaterials, particularly gold nanostars, have emerged as promising enzyme mimetic nanocatalysts due to their enhanced light interaction and superior catalytic efficiency. In this study, gold nanostars grown in situ on the surface of core-shell hydrogel beads exhibited specific oxidase-like activity when exposed to light. Photoexcitation of gold nanostars generates singlet oxygen through the interaction of positive holes and superoxide radicals, resulting in photo-oxidase-like activity. Attaching the gold nanostars to the hydrogel bead surface prevented catalytic activity loss caused by agglomeration, resulting in a marked improvement in catalytic stability. This stability is evident from the sustained catalytic activity of the hydrogel bead-embedded gold nanostars, even after 60 days of prolonged incubation in an aqueous medium, and their strong catalytic performance across multiple reaction cycles. Leveraging this photo-oxidase-like activity, a point-of-care testing (POCT) setup is developed for highly sensitive uric acid detection. The system achieved a remarkable detection limit of 0.9 μM and demonstrated excellent accuracy in blood serum and urine sample analyses. Furthermore, the integration of smartphone technology facilitated rapid and convenient on-site testing, bridging the gap between laboratory settings and real-world applications. This approach offers a practical and sustainable solution for efficient and accurate uric acid monitoring in diverse settings.

Fabrication of natural enzyme-covered / amino-modified Pd-Pt bimetallic-doped zeolitic imidazolate framework for ultrasensitive detection of metabolites

The present article introduced an natural enzyme-covered/amino-modified Pd-Pt bimetallic-doped zeolitic imidazolate framework (NAPPZ) for ultrasensitive and specific detection of glucose. The dodecahedral nanomaterial zeolitic imidazolate framework (ZIF-8)-loaded Pd-Pt bimetallic nanoparticles endowed the composite with peroxidase-like activity. The modification with glucose oxidase (GOx) facilitated the rapid access of H2O2 produced through glucose oxidation to the Pd-Pt nanoparticles vicinity reducing diffusion. GOx specifically catalyzes the transformation of glucose into H2O2, which then H2O2 rapidly migrates to the Pd-Pt nanoparticles, catalyzing the oxidation of colorless o-phenylenediamine into the orange-yellow product 2,3-diaminophenazine. Based on the aforementioned cascade reaction, the NAPPZ and NAPPZ based on ChOx were utilized for detecting glucose in human urine samples and cholesterol in milk, respectively. The NAPPZ strategy presented a broad detection range (20-1100 μmol L-1) and a low detection limit (15.9 μmol L-1) for glucose, and the NAPPZ based on ChOx strategy approach offered a broad detection range (10-500 μmol L-1) and low detection limit (6.4 μmol L-1) for cholesterol. Therefore, this novel method holds significant potential in the areas of clinical diagnostics and food safety.

Microneedle Electrode Patch Modified with Graphene Oxide and Carbon Nanotubes for Continuous Uric Acid Monitoring and Diet Management in Hyperuricemia

Hyperuricemia is a common disorder induced by purine metabolic abnormality, which will further cause chronic kidney disease, cardiovascular disease, and gout. Its main pathological characteristic is the high uric acid (UA) level in the blood, so that the detection of UA is highly important for hyperuricemia diagnosis and therapy. Herein, we report a biocompatible and minimally invasive microneedle electrode patch (MEP) for continuous UA monitoring and diet management in hyperuricemia. The composite of graphene oxide and carboxylated multiwalled carbon nanotubes was modified on the microneedle electrode surface to enhance its sensitivity, selectivity, and stability, thus realizing the continuous detection of UA in the interstitial fluid to accurately predict the UA level in the blood. This further allowed us to study the hypouricemic effect of anthocyanins on the hyperuricemia model mouse. It was found that anthocyanins extracted from blueberry can effectively inhibit the activity of xanthine oxidase to reduce the production of UA. The UA level of hyperuricemia model mice fed with anthocyanins is ∼1.7 fold lower than that of the control group. We believe that this MEP offers enormous promise for continuous UA monitoring and diet management in hyperuricemia.

Fluorescent Determination of Uric Acid Based on Porphyrin and ZnCo2O4 Nanocomposite

Advances in porphyrin chemistry have provided exciting technologies in the field of optical biosensing. Herein, we have synthesized 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP) and porous Zn0.1Co2O4 nanorods using a simple one-pot hydrothermal method. The obtained TCPP- Zn0.1Co2O4 composite was then used for the development of a novel optical sensor for the determination of uric acid (UA), which is an important biomarker in human urine, serum or saliva for the clinical diagnosis of hyperuricemia and hypouricemia, etc. TCPP-Zn0.1Co2O4 composite was characterized using SEM, TEM, EDAX, PXRD, FT-IR, UV-Visible, and NMR spectroscopic techniques. The fluorescence emission spectral analysis of TCPP-Zn0.1Co2O4 was then investigated for potential applications in the detection of uric acid via the fluorescence quenching mechanism. The designed sensor showed a linear response towards the uric acid in the concentration range of 0.99 to 5.2 nM. The optical sensor exhibits a sensitive response to uric acid with a detection limit of 0.015 nM. The sensor was employed to quantify UA in spiked human urine samples and artificial urine with satisfactory results.

Research progress of fluorescent composites based on cyclodextrins: Preparation strategies, fluorescence properties and applications in sensing and bioimaging

Fluorescence analysis has been regarded as one of the commonly used analytical methods because of its advantages of simple operation, fast response, low cost and high sensitivity. So far, various fluorescent probes, with noble metal nanoclusters, quantum dots, organic dyes and metal organic frameworks as representatives, have been widely reported. However, single fluorescent probe often suffers from some deficiencies, such as low quantum yield, poor chemical stability, low water solubility and toxicity. To overcome these disadvantages, the introduction of cyclodextrins into fluorescent probes has become a fascinating approach. This review (with 218 references) systematically covers the research progress of fluorescent composites based on cyclodextrins in recent years. Preparation strategies, fluorescence properties, response mechanisms and applications in sensing (ions, organic pollutants, bio-related molecules, temperature, pH) and bioimaging of fluorescent composites based on cyclodextrins are summarized in detail. Finally, the current challenges and future perspectives of these composites in relative research fields are discussed.

Advancing stroke therapy: the potential of MOF-based nanozymes in biomedical applications

In this study, we explored the growing use of metal-organic framework (MOF)-based Nanozymes in biomedical research, with a specific emphasis on their applications in stroke therapy. We have discussed the complex nature of stroke pathophysiology, highlighting the crucial role of reactive oxygen species (ROS), and acknowledging the limitations of natural enzymes in addressing these challenges. We have also discussed the role of nanozymes, particularly those based on MOFs, their structural similarities to natural enzymes, and their potential to improve reactivity in various biomedical applications. The categorization of MOF nanozymes based on enzyme-mimicking activities is discussed, and their applications in stroke therapy are explored. We have reported the potential of MOF in treating stroke by regulating ROS levels, alleviation inflammation, and reducing neuron apoptosis. Additionally, we have addressed the challenges in developing efficient antioxidant nanozyme systems for stroke treatment. The review concludes with the promise of addressing these challenges and highlights the promising future of MOF nanozymes in diverse medical applications, particularly in the field of stroke treatment.

The Application of Metal-Organic Frameworks in Water Treatment and Their Large-Scale Preparation: A Review

Over the last few decades, there has been a growing discourse surrounding environmental and health issues stemming from drinking water and the discharge of effluents into the environment. The rapid advancement of various sewage treatment methodologies has prompted a thorough exploration of promising materials to capitalize on their benefits. Metal-organic frameworks (MOFs), as porous materials, have garnered considerable attention from researchers in recent years. These materials boast exceptional properties: unparalleled porosity, expansive specific surface areas, unique electronic characteristics including semi-conductivity, and a versatile affinity for organic molecules. These attributes have fueled a spike in research activity. This paper reviews the current MOF-based wastewater removal technologies, including separation, catalysis, and related pollutant monitoring methods, and briefly introduces the basic mechanism of some methods. The scale production problems faced by MOF in water treatment applications are evaluated, and two pioneering methods for MOF mass production are highlighted. In closing, we propose targeted recommendations and future perspectives to navigate the challenges of MOF implementation in water purification, enhancing the efficiency of material synthesis for environmental stewardship.

Alumina inorganic molecularly imprinted polymer modified multi-walled carbon nanotubes for uric acid detection in sweat

Alumina inorganic molecularly imprinted polymer (MIP) modified multi-walled carbon nanotubes (MWCNTs) on a glassy carbon electrode (MWCNTs-Al2O3-MIP/GCE) was firstly designed and fabricated by one-step electro deposition technique for the detection of uric acid (UA) in sweat. The UA templates were embedded within the inorganic MIP by co-deposition with Al2O3. Through the evaluation of morphology and structure by Field Emission Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM), it was verified that the specific recognition sites can be fabricated in the electrodeposited Al2O3 molecular imprinted layer. Due to the high selectivity of molecular imprinting holes, the MWCNTs-Al2O3-MIP/GCE electrode demonstrated an impressive imprinting factor of approximately 2.338 compared to the non-molecularly imprinted glassy carbon electrode (MWCNTs-Al2O3-NIP/GCE) toward uric acid detection. Moreover, it exhibited a remarkable limit of detection (LOD) of 50 nM for UA with wide detection range from 50 nM to 600 μM. The MWCNTs-Al2O3-MIP/GCE electrode also showed strong interference resistance against common substances found in sweat. These results highlight the excellent interference resistance and selectivity of MWCNTs-Al2O3-MIP/GCE sensor, positioning it as a novel sensing platform for non-invasive uric acid detection in human sweat.

p-Thiocresol Functionalized Cesium Lead Bromide (PTC@CsPbBr3): A Fluorometric Sensing Probe for the Detection of Cholesterol

Inorganic halide-based perovskites (e.g., cesium lead bromide) are tremendously useful semiconducting materials due to their unique optoelectronic properties. However, degradation of these perovskites under humid conditions is one of the major drawbacks to prevent their wide applications. Herein, passivated cesium lead bromide nanoparticles are synthesized using p-thiocresol as a passivating ligand, and this stable version of perovskite is later applied successfully as a sensor probe towards cholesterol detection. The designed sensor can detect cholesterol with a lower detection limit of 0.24 ppm and a fast response time of 10 s. The mechanism of quenching PTC@CsPbBr3 upon the gradual addition of cholesterol is discussed. Further, the sensor is successfully applied in the detection of cholesterol in real samples (blood serum). This work presents PTC@CsPbBr3 as a novel sensing platform for detecting cholesterol well in biomedical applications.

Intelligent quantitative recognition of sulfide using machine learning-based ratiometric fluorescence probe of metal-organic framework UiO-66-NH2/Ppix

Sulfides possess either high toxicity or play crucial physiological role such as gas transmitter dependent upon dosage, hence the significant for their rapid sensitive and selective concentration determination. Herein, a machine learning enhanced ratiometric fluorescence sensor was engineered for sulfide determination by incorporating the nanometal-organic framework (UiO-66-NH2) along with protoporphyrin IX (Ppix). The blue fluorescence at 431 nm originated from the moiety of UiO-66-NH2 by 365 nm excitation serves as an internal calibration reference signal, while the red fluorescence at 629 nm from the moiety of Ppix serves as the analytical signal, and the intensity is correlated to the amount of sulfides. The fluorescence color of the sensor gradually varies from blue to red upon sequential addition of copper and sulfide ions, resulting in RGB (Red, Green, Blue) feature values for corresponding sulfide concentrations, which facilities the advanced data processing techniques using machine learning algorithms. On the basis of fluorescence image fingerprint extraction and machine learning algorithms, an online data analysis model was developed to improve the precision and accuracy of sulfide determination. The established model employed Linear Discriminant Analysis (LDA) and was subjected to rigorous cross-validation to ensure its robustness. By analyzing the correlation between RGB feature values and sulfide concentrations, the study highlighted a significant positive relationship between the red feature values and sulfide concentrations. The application of machine learning techniques on the ratiometric fluorescence signal of the UiO-66-NH2/Ppix probe demonstrated its potential for intelligent quantitative determination of sulfides, offering a valuable and efficient tool for pollution detection and real-time rapid environmental monitoring.

Au nanoparticle-embellished UiO-66 on reduced graphene oxide as a non-enzymatic electrocatalyst at a remarkably low oxidation potential for glucose oxidation and sensing

Au nanoparticle-embellished metal-organic framework UiO-66 on reduced graphene oxide (Au/UiO-66/rGO) was synthesized. Au/UiO-66/rGO displayed strong electrocatalytic activity for oxidation of glucose in alkaline solution at a remarkably low oxidation potential of +0.20 V vs. Ag/AgCl. Au nanoparticles played a paramount role in the catalytic oxidation of glucose at the electrode, while both rGO and UiO-66 can significantly enhance the current responses to glucose. The resulting non-enzymatic glucose sensor exhibited a wide range of linear response, high sensitivity and selectivity for the determination of glucose. The sensor was successfully applied for the determination of glucose in honey products.

A luminescent MOF-based nonenzymatic probe for colorimetric/photothermal/fluorescence triple-mode assay of uric acid in body fluids

Monitoring the levels of uric acid (UA) in body fluids is of great significance in the clinical diagnosis and therapy of related diseases. Herein, a novel nanocomposite R6G@Fe-MOF based nonenzymatic probe is presented to provide a ratiometric fluorescent, colorimetric, and photothermal triple read-out signal for the visual, sensitive, and convenient assay of UA. The framework structure of the in situ encapsulated R6G@Fe-MOF is found to decompose upon the addition of UA, resulting in the reduction of Fe3+ to Fe2+. This reduction will lead to a rapid increase in fluorescence emission (FL) at 430 nm. Simultaneously, the FL at 573 nm will decrease remarkably due to the inner filter effect (IFE) between UA and R6G@Fe-MOF. Furthermore, the reaction of the generated Fe2+ with potassium ferricyanide (K3 [Fe(CN)6]) can in situ generate Prussian blue (PBNPs) with outstanding color and photothermal properties, which allow for easy colorimetric and photothermal signal readout. The detection limits (LOD) for the colorimetric, fluorometric and photothermal detection are low at 1.68 μM, 0.236 μM, and 1.32 μM respectively. Ultimately, it is successfully employed to determine UA in urine, serum, and saliva, yielding satisfactory results. The constructed R6G@Fe-MOF sensor provides a simple, sensitive, and accurate determination of UA that can be tailored to meet the needs of various applications, and also provides new perspectives for the design and development of versatile sensors for diverse uses.

A pH-Stable Tb-MOF as Luminescence Sensor for Highly Sensitive Detection of Amino Acids through Diverse Sensing Mechanism

A luminescent Tb-MOF with excellent stability and dual-emitting properties was constructed with an amide-functionalized tetracarboxylate ligand. Tb-MOFs were initially assembled on one-dimensional Tb3+ chains, then formed a two-dimensional double-decker layer through the synergistic linking of organic ligands and bridging formic acid anions, and further fabricated the final three-dimensional structure through the connection of the organic ligands. Powder X-ray diffraction experiments revealed that Tb-MOFs not only exhibited excellent stability in water but also maintained structural integrity in the pH range of 2-12. Importantly, this Tb-MOF provided the first example of a metal-organic framework (MOF)-based luminescence sensor that can simultaneously detect two acid amino acids (aspartic and glutamic acids) through a turn-off sensing mechanism and two basic amino acids (lysine and arginine acids) through unusual turn-on and turn-off-on sensing mechanisms. Moreover, high sensitivity, low detection limit, and excellent recyclability of this sensor endow Tb-MOFs with great potential as a highly efficient amino acid fluorescence sensor in chemical detection and biological environments.

Review on Uric Acid Recognition by MOFs with a Future in Machine Learning

Uric acid (UA) is produced from purine metabolism and serves as a prevalent biomarker for multiple diseases including cancer. Hyperuricemia or hypouricemia can cause multiple dysfunctions throughout the biological processes. Consequently, there is a pressing need for monitoring UA concentration in body fluid. While clinical methods are known, the availability of a point-of-care testing (PoCT) kit remains conspicuously absent. In the case of electrochemical recognition of UA, the oxidation potential of ascorbic acid closely aligns with that of UA and thus it hinders the detection process, which eventually may result in false positive signals. Several chemosensors are known in the field of supramolecular chemistry, and metal-organic frameworks (MOFs) are one of the best-performing contenders due to their robustness, stability, and versatile structures. In this review, we tried to unbox the up-to-date development of UA sensing by MOFs. We delve into the state of UA recognition by MOFs, exploring both electrochemical and fluorometric pathways and drawing comparisons with structurally similar probes like covalent organic frameworks (COFs) to understand/establish the advantages of MOFs specifically in UA sensing. In the absence of a PoCT kit, we have provided the conceptual outlook for designing a PoCT device termed a "Urimeter" via electrochemical operation. For the first time, we have proposed different methods of how UA sensing can be tied up with artificial intelligence and machine learning (AI-ML).

Progress in optical sensors-based uric acid detection

The escalating number of patients affected by various diseases, such as gout, attributed to abnormal uric acid (UA) concentrations in body fluids, has underscored the need for rapid, efficient, highly sensitive, and stable UA detection methods and sensors. Optical sensors have garnered significant attention due to their simplicity, cost-effectiveness, and resistance to electromagnetic interference. Notably, research efforts have been directed towards UA on-site detection, enabling daily monitoring at home and facilitating rapid disease screening in the community. This review aims to systematically categorize and provide detailed descriptions of the notable achievements and emerging technologies in UA optical sensors over the past five years. The review highlights the advantages of each sensor while also identifying their limitations in on-site applications. Furthermore, recent progress in instrumentation and the application of UA on-site detection in body fluids is discussed, along with the existing challenges and prospects for future development. The review serves as an informative resource, offering technical insights and promising directions for future research in the design and application of on-site optical sensors for UA detection.

Green-Mediated Synthesis of NiCo2O4 Nanostructures Using Radish White Peel Extract for the Sensitive and Selective Enzyme-Free Detection of Uric Acid

The ability to measure uric acid (UA) non-enzymatically in human blood has been demonstrated through the use of a simple and efficient electrochemical method. A phytochemical extract from radish white peel extract improved the electrocatalytic performance of nickel-cobalt bimetallic oxide (NiCo2O4) during a hydrothermal process through abundant surface holes of oxides, an alteration of morphology, an excellent crystal quality, and increased Co(III) and Ni(II) chemical states. The surface structure, morphology, crystalline quality, and chemical composition were determined using a variety of analytical techniques, including powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and X-ray photoelectron spectroscopy (XPS). The electrochemical characterization by CV revealed a linear range of UA from 0.1 mM to 8 mM, with a detection limit of 0.005 mM and a limit of quantification (LOQ) of 0.008 mM. A study of the sensitivity of NiCo2O4 nanostructures modified on the surface to UA detection with amperometry has revealed a linear range from 0.1 mM to 4 mM for detection. High stability, repeatability, and selectivity were associated with the enhanced electrochemical performance of non-enzymatic UA sensing. A significant contribution to the full outperforming sensing characterization can be attributed to the tailoring of surface properties of NiCo2O4 nanostructures. EIS analysis revealed a low charge-transfer resistance of 114,970 Ohms that offered NiCo2O4 nanostructures prepared with 5 mL of radish white peel extract, confirming an enhanced performance of the presented non-enzymatic UA sensor. As well as testing the practicality of the UA sensor, blood samples from human beings were also tested for UA. Due to its high sensitivity, stability, selectivity, repeatability, and simplicity, the developed non-enzymatic UA sensor is ideal for monitoring UA for a wide range of concentrations in biological matrixes.

Bioconjugation of nanozyme and natural enzyme to enable a one-step cascade reaction for the detection of metabolites

Nanozyme, with enzyme-mimicking activity and excellent stability, has attracted extensive attention. However, some inherent disadvantages, including poor dispersion, low selectivity, and insufficient peroxidase-like activity, still limit its further development. Therefore, an innovative bioconjugation of a nanozyme and natural enzyme was conducted. In the presence of graphene oxide (GO), histidine magnetic nanoparticles (H-Fe₃O₄) were first synthesized by a solvothermal method. The GO-supported H-Fe₃O₄ (GO@H-Fe₃O₄) exhibited superior dispersity and biocompatibility because GO was the carrier and possessed outstanding peroxidase-like activity because of the introduction of histidine. Furthermore, the mechanism of the peroxidase-like activity of GO@H-Fe₃O₄ was the generation of •OH. Uric acid oxidase (UAO) was selected as the model natural enzyme and covalently linked to GO@H-Fe₃O₄ with hydrophilic poly(ethylene glycol) as a linker. UAO could specifically catalyze the oxidation of uric acid (UA) to generate H₂O₂, and subsequently, the newly produced H₂O₂ oxidized the colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue ox-TMB under the catalysis of GO@H-Fe₃O₄. Based on the above cascade reaction, the GO@H-Fe₃O₄-linked UAO (GHFU) and GO@H-Fe₃O₄-linked ChOx (GHFC) were used for the detection of UA in serum samples and cholesterol (CS) in milk, respectively. The method based on GHFU exhibited a wide detection range (5-800 μM) and a low detection limit (1.5 μM) for UA, and the method based on GHFC exhibited a wide detection range (4-400 μM) and a low detection limit (1.13 μM) for CS. These results demonstrated that the proposed strategy had great potential in the field of clinical detection and food safety.

Bioconjugation of nanozyme and natural enzyme for ultrasensitive detection of cholesterol

When nanozymes are used in biological analysis, higher activity can improve the detection sensitivity, and better selectivity can eliminate other interference. To improve the specificity and sensitivity, we fabricated an innovative bioconjugated nanozyme with natural enzyme (BNNZ), in which natural ChOx was immobilized onto histidine-modified Fe₃O₄ (His-Fe₃O₄) with hydrophilic poly(ethylene glycol) (PEG) as a linker. ChOx could specifically catalyze the oxidation of cholesterol to generate H₂O₂ molecule, and then the newly formed H₂O₂ oxidized the colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue ox-TMB by peroxidase-like His-Fe₃O₄. According to the above cascade reaction, the BNNZ-based colorimetric strategy was proposed for the detection of cholesterol. Wherein, natural enzymes specifically catalyzed substrates, which endowed BNNZ with excellent specificity for target molecules; meanwhile, the introduction of histidine on His-Fe₃O₄ effectively increased the peroxidase-like activity of BNNZ, which provided a guarantee for sensitivity. Furthermore, BNNZ after reaction could be rapidly separated by an external magnetic field without interfering with colorimetric quantitative detection. The proposed strategy exhibited excellent sensitivity with limit of detection of 0.446 μM and was successfully used for the detection of cholesterol in spiked human serum sample with recovery and relative standard deviation in the range of 97.9-103.5% and 2.5-4.0%, respectively. This work indicates that the bioconjugation of nanozyme and natural enzyme may be a universal strategy for synthesis of high-performance enzyme-nanozyme systems, and the new-type BNNZ will be widely used in biological detection and disease treatment.

L-histidine functionalized ZiF-8 with aggregation-induced emission for detection of tetracycline

In this study, we constructed zinc based metal-organic framework functionalized by L-histidine (His@ZiF-8). The His@ZiF-8 had high porosity, large surface area, abundant carboxyl and amino group, which has been found to greatly enhance the aggregation-induced emission (AIE) of tetracycline (TC). After the His@ZiF-8 enrichment with TC, the TC exhibited strong fluorescence emission peak at 565 nm based on AIE. Under the optimal conditions, the fluorescence intensity of TC exhibited a good linear relationship with TC concentration within 0.1-80 μM with a low limit of detection of 28.6 nM. Antibiotic analogs such as neomycin, chloramphenico, ampicillin, kanamycin, and erythromycin have no obvious interference. In addition, the developed method was successfully used to the detection of TC in milk, river water, and honey.

Rhodamine B functionalized luminescent metal-organic frameworks for ratiometric fluorescence sensing of hydroquinone

The development of sensitive and selective detection methods for hydroquinone (HQ), a phenolic organic compound with high toxicity and low degradability, is of extraordinary importance. In this work, a fluorescent sensor based on functionalized luminescent metal-organic frameworks (LMOFs) was designed and applied for the ratiometric fluorescence sensing of HQ. The sensor was prepared by the functionalization of IRMOF-3 with rhodamine B (RhB), possessing dual-emission fluorescence properties. After the addition of HQ, the blue fluorescence of the IRMOF-3 framework was gradually weakened, while the red fluorescence of RhB remained unchanged, resulting in the continuous fluorescence change of RhB@IRMOF-3 with HQ concentrations. The sensing mechanism demonstrates that HQ changes the fluorescence of the sensor via electron transfer between benzoquinone and RhB@IRMOF-3. The RhB@IRMOF-3 sensor has the advantages of a wide linear range, quick response speed, and strong specificity for HQ detection. This work is the first attempt focusing on functionalized LMOFs for HQ fluorescence detection, which has superb potential for the application to real environmental water samples.

Recent advances in nanomaterials-based optical sensors for detection of various biomarkers (inorganic species, organic and biomolecules)

This review briefly emphasizes the different detection approaches (electrochemical sensors, chemiluminescence, surface-enhanced Raman scattering), functional nanostructure materials (quantum dots, metal nanoparticles, metal nanoclusters, magnetic nanomaterials, metal oxide nanoparticles, polymer-based nanomaterials, and carbonaceous nanomaterials) and detection mechanisms. Further, this review emphasis on the integration of functional nanomaterials with optical spectroscopic techniques for the identification of various biomarkers (nucleic acids, glucose, uric acid, oxytocin, dopamine, ascorbic acid, bilirubin, spermine, serotonin, thiocyanate, Pb²⁺ , Cu²⁺ , Hg²⁺ , F^- , peptides, and cancer biomarkers (mucin 1, prostate specific antigen, carcinoembryonic antigen, CA15-3, human epidermal growth factor receptor 2, C-reactive protein, and interleukin-6). Analytical characteristics of nanomaterials-based optical sensors are summarized in Tables, providing the insights of nanomaterials-based optical sensors for biomarkers detection. Finally, the opportunities and challenges of nanomaterials-based optical analytical approaches for the detection of various biomarkers (inorganic, organic, biomolecules, peptides and proteins) are discussed.

NH3 Plasma Functionalization of UiO-66-NH2 for Highly Enhanced Selective Fluorescence Detection of U(VI) in Water

Radioactive U(VI) in nuclear wastewater is a global environmental pollutant that poses a great threat to human health. Therefore, it is of great significance to develop a U(VI) sensor with desirable sensitivity and selectivity. Inspired by electron-donating group modification for enhancement of binding affinity toward U(VI), we report an amine group functionalization of UiO-66-NH₂, using a low-cost, environmentally friendly, and low-temperature NH₃ plasma technique as a fluorescence switching nanoprobe for highly sensitive and selective detection of U(VI). The resulting amine-functionalized UiO-66-NH₂ (LTP@UiO-66-NH₂) shows dramatically enhanced fluorescence emission and selective sensitivity for U(VI) on the basis of the quenching effect. The quenching efficiency increases from 58 to 80% with the same U(VI) concentration (17.63 μM) after NH₃ plasma functionalization. As a result, the LTP@UiO-66-NH₂ has the best K_sv (1.81 × 10⁵ M^-1, 298 K) and among the lowest LODs (0.08 μM, 19.04 ppb) compared with those reported in the literature. Intraday and interday precision and application in real environment experiments indicate stable and accurate U(VI) detection performance. Fluorescence lifetime and temperature-dependent detection experiments reveal that the quenching mechanism belongs to the static quenching interaction. The highly selective fluorescence detection is attributed to the selective binding of U(VI) by the rich functionalized amine groups of LTP@UiO-66-NH₂. This work provides an efficient fluorescence probe for highly sensitive U(VI) detection in water, and a new strategy of tailored plasma functionalization for developing a practical MOF sensor platform for enhanced fluorescence emission, sensitivity, and selectivity for detecting trace amounts of radioactive species in the environment.

Selectivity Enhancement for Uric Acid Detection via In Situ Preparation of Blue Emissive Carbon Dots Entrapped in Chromium Metal-Organic Frameworks

In the present work, for the first time, the in situ formation of blue emissive carbon dots (bCDs) and encapsulation into the pores of chromium-based metal-organic frameworks (Cr-MOFs) are described. The luminescent bCDs via in situ process are formed and entrapped inside the pores of Cr-MOFs to form a nanocomposite of bCDs@Cr-MOFs. The bCDs@Cr-MOFs showed a strong broad blue emission at 420 nm (excited at 310 nm), which corresponds to both, the ligand (2-aminoterephthalic acid) in the Cr-MOF and the entrapped bCDs. This is assigned for the entrapping of bCDs in the pores of the MOFs. Additionally, transmission electron microscopy (TEM) images showed two types of particles, 150 rod-like shapes for Cr-MOF and 5-10 nm spherical shapes assigned for the presence of bCDs. The bCDs alone (without Cr-MOF) showed no selectivity, and their emission was quenched by different biomolecules and ions, such as ascorbic acid, uric acid, Fe³⁺, Cu²⁺, and Hg²⁺. The selectivity of bCDs toward uric acid was increased dramatically when they were encapsulated in the Cr-MOF. The linear range for uric acid was 20-50 μM, and the LOD was measured as 1.3 μM. Spike recoveries for the detection of uric acid in serum samples were between 94 and 108%. The relative standard deviation (RSD, n = 3) at each concentration value was less than 2%. The results showed high ruggedness and robustness of the assay due to its high shelf-life stability of probe (four weeks), water stability, and long working pH range. Validation experiments showed that the established MOF-based sensing system is appropriate for uric acid detection in real samples.

Two Multiresponsive Luminescent Zn-MOFs for the Detection of Different Chemicals in Simulated Urine and Antibiotics/Cations/Anions in Aqueous Media

Two Zn-MOFs, namely, {[Zn(L)_0.5(bpea)]·0.5H₂O·0.5DMF}_n [LCU-113 (for Liaocheng University)] and {[Zn(L)_0.5(ibpt)]·H₂O·DMF}_n (LCU-114), were synthesized based on flexible tetracarboxylic acid 1,3-bis(3,5-dicarboxyphenoxy)benzene (H₄L) and different N-ligands [bpea = 1,2-dipyridyl ethane; ibpt = 3-(4'-imidazolobenzene)-5-(pyridine-4'-yl)-1,2,4-triazole]. LCU-113 and LCU-114 possess twofold interpenetrating three-dimensional pillared layer structures, in which a two-dimensional layer formed by carboxylic acid and Zn²⁺ ions was pillared by bpea and ibpt, respectively. The two complexes show high water stability and high luminescence sensing performance toward organic solvents, ions, and antibiotics, as well as chemicals, in simulated urine. The investigation showed that (1) LCU-113 and LCU-114 could detect uric acid (UA, 2,6,8-trihydroxypurine, metabolite of purine) and p-aminophenol (PAP, biomarker of phenamine) in simulated urine by luminescence quenching, respectively, and (2) luminescence quenching of LCU-113 and LCU-114 occurred in aqueous solutions of nitrofurazone (NZF), Fe³⁺, and CrO₄^2-/Cr₂O₇^2-. All the above detections have excellent anti-interference ability and recyclability. The luminescence mechanism analysis indicates that weak interactions between the framework structures and the target analytes as well as the energy competition (inner filter effect) play an important role in sensing the above analytes. The practical application for monitoring NZF/Fe³⁺ in water samples was also tested.

Diamino group-functionalized Zr-based metal-organic framework for fluorescence sensing of free chlorine in the aqueous phase and Knoevenagel condensation

We developed a porous diamino group-functionalized Zr(IV) metal-organic framework (MOF). The synthesized MOF has a similar structure to DUT-52 (DUT = Dresden University of Technology), which has a face-centered cubic structure with an Fm3̄m space group. The synthesized material (DUT-52-(NH2)2-1) was solvent exchanged with methanol (MeOH) and activated at 100 °C overnight. Both the as-synthesized and activated materials (DUT-52-(NH2)2-1') are thermally stable until 300 °C. The Brunauer-Emmett-Teller (BET) surface area of DUT-52-(NH2)2-1' was found to be 413 m² g^-1. DUT-52-(NH2)2-1' showed a significant quenching of fluorescence response after coming in contact with free chlorine (ClO^-) in an aqueous medium. The selectivity of DUT-52-(NH2)2-1' towards ClO^- was not significantly hampered in the presence of any competitive ion. The limit of detection (LOD) value was found to be 0.08 μM in phosphate-buffered saline (PBS, pH = 7.4). DUT-52-(NH2)2-1' is recyclable and very sensitive towards ClO^-. Moreover, the paper strip method was developed for onsite identification of ClO^-. Furthermore, the catalytic activity of DUT-52-(NH2)2-1' was tested in the Knoevenagel condensation between benzaldehyde and cyanoacetamide. The experimental results clearly indicate that DUT-52-(NH2)2-1' exhibits high activity with very high selectivity towards condensation products. The solid was reusable three times with no decay in its activity, as evidenced by powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM) and fourier transform infrared (FT-IR).

Silver nanoparticles combined with amino-functionalized UiO-66 for sensitive detection of glutathione

Herein, a fluorescent nanosensor has been constructed for detection of glutathione (GSH) based on NH₂-UiO-66 and AgNPs. The NH₂-UiO-66 was synthesized where 2-amino-terephthalic acid as the organic ligand and Zr⁴⁺ as the center metal ions. The AgNPs can enhance the fluorescence of NH₂-UiO-66 based on metal enhanced fluorescence (MEF) effect. Moreover, in the present of GSH, the fluorescence of NH₂-UiO-66@AgNPs was quenched via electrostatic interaction and Ag-S reaction. The present sensing strategy shows good linear relation with the concentration of GSH in the range of 0.2-1.0 μM and 1.0-30 μM, and the limit of detection is 79 nM. Furthermore, our fluorescent nanosensor was utilized to detect GSH in human serum with a recovery of 96.8-102.5%. The results indicated that NH₂-UiO-66@AgNPs is successfully applied for high sensitive and selective detection of GSH in human serum.

Upconversion-nanoparticle-functionalized Janus micromotors for efficient detection of uric acid

We report enzyme-powered upconversion-nanoparticle-functionalized Janus micromotors, which are prepared by immobilizing uricase asymmetrically onto the surface of silicon particles, to actively and rapidly detect uric acid. The asymmetric distribution of uricase on silicon particles allows the Janus micromotors to display efficient motion in urine under the propulsion of biocatalytic decomposition of uric acid and simultaneously detect uric acid based on the luminescence quenching effect of the UCNPs modified on the other side of SiO₂. The efficient motion of the motors greatly enhances the interaction between UCNPs and the quenching substrate and improves the uric acid detection efficiency. Overall, such a platform using uric acid simultaneously as the detected substrate and motion fuel offers considerable promise for developing multifunctional micro/nanomotors for a variety of bioassay and biomedical applications.

Metal–organic frameworks (MOFs) as fluorescence sensors: principles, development and prospects

This review classifies the latest developments of MOF-based fluorescence sensors according to the analytes, and discusses the challenges faced by MOF-based fluorescence sensors and promotes some directions for future research.

A novel 3D coordination polymer constructed by dual-ligand for highly sensitive detection of purine metabolite uric acid

Uric acid (UA), as the final product of purine metabolism, exists in urine and serum, which plays an important role in human metabolism, immunity and other functions. The sensitive, efficient, and rapid detection of UA has far-reaching significance in clinical diagnosis and disease prevention. Herein, a novel coordination polymer constructed by dual-ligand was successfully prepared, which exhibited excellent thermal and water stability. The polymer was interlaced by coordination bonds and hydrogen bonds to form an infinitely extended three-dimensional framework, which showed a rare and novel topological structure. The complex selectively recognized UA through significant fluorescence quenching response in the presence of various interferences. The excellent detection sensitivity (the limited detection of 1.2 μM), outstanding anti-interference ability and remarkable recyclability marked the complex to be a promising sensor material towards UA. In addition, the detection mechanism of UA by the complex was investigated in detail by combining density functional theory (DFT) and a variety of other analytical methods.

A Comparison of Uric Acid Optical Detection Using as Sensitive Materials an Amino-Substituted Porphyrin and Its Nanomaterials with CuNPs, PtNPs and Pt@CuNPs

Hybrid nanomaterials consisting in 5,10,15,20-tetrakis(4-amino-phenyl)-porphyrin (TAmPP) and copper nanoparticles (CuNPs), platinum nanoparticles (PtNPs), or both types (Pt@CuNPs) were obtained and tested for their capacity to optically detect uric acid from solutions. The introduction of diverse metal nanoparticles into the hybrid material proved their capacity to improve the detection range. The detection was monitored by using UV-Vis spectrophotometry, and differences between morphology of the materials were performed using atomic force microscopy (AFM). The hybrid material formed between porphyrin and PtNPs hasthe best and most stable response for uric acid detection in the range of 6.1958 × 10−6–1.5763 × 10−5 M, even in the presence of very high concentrations of the interference species present in human environment.

Post-synthetically modified metal-organic frameworks for sensing and capture of water pollutants

Thanks to a bottom-up design of metals and organic ligands, the library of metal-organic frameworks (MOFs) has seen a conspicuous growth. Post-synthetically modified MOFs comprise a relatively smaller subset of this library. Whereas the approach of post-synthetic modification was seminally introduced for MOFs in the early 1990s, the earliest examples of post-synthetically modified MOFs are only congruous with adsorption and catalysis. The utility of PSM-derived MOFs for the sensing and capture of water contaminants is relatively niche. Arguably though, an increasing number of post-synthetically modified MOFs are finding relevance in the context of water pollutant remediation. In this article, we review the recent advances in this area and propose a structure-function relationship-guided blueprint for the future outlook.

Structure Defect Tuning of Metal-Organic Frameworks as a Nanozyme Regulatory Strategy for Selective Online Electrochemical Analysis of Uric Acid

Nanozymes have been designed to address the limitations of high cost and poor stability involving natural enzymes in analytical applications. However, the catalytic efficiency of the nanozyme still needs to be improved so that it can meet the selectivity and stability requirements of accurate biomolecule analysis. Here, we presented structure defects of metal-organic frameworks (MOFs) as a tuning strategy to regulate the catalytic efficiency of artificial nanozymes and investigated the roles of defects on the catalytic activity of oxidase-like MOFs. Structural defects were introduced into a novel Co-containing zeolitic imidazolate framework with gradually loosened morphology (ZIF-L-Co) by doping cysteine (Cys). It was found that with the increase in defect degree, the properties of materials such as ascorbate oxidase-like, glutathione oxidase-like, and laccase-like were obviously enhanced by over 5, 2, and 3 times, respectively. In-depth structural investigations indicate that the doping of sulfur inducing structural defects which may destroy the equilibrium state between cobalt and nitrogen in 2-methylimidazole and distort the crystal lattice, thereby enhancing the adsorption of oxygen and thus promoting the oxidase-like activity. The ZIF-L-Co-10 mg with enhanced ascorbate oxidase- and laccase-like activity was loaded into a microreactor and integrated into an online electrochemical system (OECS) in the upstream of the detector. This nanozyme-based microreactor can completely remove ascorbic acid, dopamine, and 3,4-dihydroxyphenylacetic acid which are the main interference toward uric acid (UA) electrochemical measurement, and the ZIF-L-Co-10 mg Cys-based OECS system is capable of continuously capturing UA change in rat brain following ischemia-reperfusion injury. Structure defect tuning of ZIF-L-Co not only provides a new regulatory strategy for artificial nanozyme activity but also provides a critical chemical platform for the investigation of UA-related brain function and brain diseases.

Electrochemical sensing behavior of graphdiyne nanoflake towards uric acid: a quantum chemical approach

Though the gas sensing applications of graphdiyne have widely reported; however, the biosensing utility of graphdiyne needs to be explored. This study deals with the sensitivity of graphdiyne nanoflake (GDY) towards the uric acid (UA) within the density functional framework. The uric acid is allowed to interact with graphdiyne nanoflake from all the possible orientations. Based on these interacting geometries, the complexes are differentiated with naming, i.e., UA1@GDY, UA2@GDY, UA3@GDY, and UA4@GDY (Fig. 1). The essence of interface interactions of UA on GDY is derived by computing geometric, energetic, electronic, and optical properties. The adsorbing affinity of complexes is evaluated at ωB97XD/6-31 + G(d, p) level of theory. The stabilities of the complexes are quantified through the interaction energies (E_int) with reasonable accuracy. The calculated E_int of the UA1@GDY, UA2@GDY, UA3@GDY, and UA4@GDY complexes are - 31.13, - 25.87, - 20.59, and - 16.54 kcal/mol, respectively. In comparison with geometries, it is revealed that the higher stability of complexes is facilitated by π-π stacking. Other energetic analyses including symmetry adopted perturbation theory (SAPT), noncovalent interaction index (NCI), and quantum theory of atoms in molecule (QTAIM) provide the evidence of dominating dispersion energy in stabilizing the resultant complexes. The HOMO-LUMO energies, NBO charge transfer, and UV-vis analysis justify the higher electronic transition in UA1@GDY, plays a role of higher sensitivity of GDY towards the π-stacked geometries over all other possible interaction orientations. The present findings bestow the higher sensitivity of GDY towards uric acid via π-stacking interactions. Fig. 1 Optimized geometries (with interaction distances in Å) of UA@GDY complexes.

A novel metal organic gel with superior oxidase-like activity for efficient and sensitive chemiluminescence detection of uric acid

It is found that MIL-100(Fe) gels, as a kind of metal-organic gels (MOGs), constitutting of iron (Fe³⁺) and trimesic acid (H₃BTC), has been regarded as the efficient catalyst of luminol chemiluminescence (CL) system without the presence of extra oxidants in the present work. MIL-100(Fe) gels that have possessed mimicking oxidase-like activity can excellently enhanced luminol CL intensity by accelerating the generation of reactive oxygen species. Furthermore, with the addition of uric acid (UA), the CL signal has been dramatically inhibited under alkaline condition. Hence, the CL intensity inhibiting ratio (I₀/I_S) was proportional to the increasing concentration of UA in the rang from 10 nM to 4000 nM with the detection limit of 5.9 nM. This method has been successfully applied for analysis of UA with acceptable recoveries ranging from 97.0% to 107.9% in urine sample. These results indicates that this study open up a novel, sensitive and convenient method to detect UA in biological samples.

Mixed functionalization strategy on indium-organic framework for multiple ion detection and H2O2 turn-on sensing

A special functional group mediated functionalization platform is introduced as a new and versatile platform tool to improve the fluorescence detection performance of metal-organic frameworks (MOF). The creation of a mixed-functionalization strategy on a MOF realizes the high sensitivity detection of heavy metal ions, anions and small molecules. In this work, we have first reported a novel amino functionalized 3D indium MOF [In(BDC-NH2)(OH)]n (In1-NH2) which not only has an excellent fluorescent characteristic but also shows highly sensitive identification of Fe3+, Cu2+, Pb2+ and ClO- in water with broad linear ranges and short response times. Subsequently, based on the remaining amino group site of In1-NH2, a post-synthetic modification strategy is utilized to introduce an active boronic acid group for hydrogen peroxide detection. The obtained PBA-In1 exhibits an efficient sensing performance for hydrogen peroxide with an LOD of 0.42 μM. Given this, PBA-In1 is expected to become an effective probe to monitor the formation of metabolites in humans. In1-NH2 successfully achieves multiple ion detection and the PBA-In1 sensing platform with boronic acid functionalization may have good application prospects in biochemical research in the future.

Recyclable Luminescence Sensor for Dinotefuran in Water by Stable Cadmium-Organic Framework

Due to the widespread use of dinotefuran around the world, its impact on food and environmental safety has aroused great concern, and the establishment of a rapid and convenient approach for dinotefuran detection is necessary but challenging. Herein, we synthesized a unique three-dimensional framework {[(CH₃)₂NH₂]₂[Cd₃(BCP)₂]·10H₂O·3.5DMF}_n (1). Single-crystal X-ray analysis indicates that 1 possesses a 4,8-connected anion framework that corresponds to alb topology, with a one-dimensional rectangular channel along the c-axis with the size of 4 Å × 10 Å. Compound 1 displays satisfactory solvent and thermal stability. Luminescent investigations reveal that 1 can selectively detect dinotefuran by fluorescence quenching among other pesticides, displaying excellent anti-interference performance with common ions in water. Importantly, the limit of detection is as low as 2.09 ppm, which is far below the residual concentration of the U.S. food standard. A fluorescence quenching mechanism study shows that there exists competitive energy absorption and static quenching processes. To our knowledge, 1 is the first MOF-based fluorescence probe for dinotefuran detection.

A novel fluorescent strategy based on double modifications of metal organic framework material CAU-10-NH2 for low background and high sensitivity determination of H2S

Hydrogen sulfide is typical metabolic marker and environmental pollutant which is worthwhile to determine. Herein, a low background and high sensitivity fluorescent strategy based on double modifications of metal organic framework material CAU-10-NH₂ is proposed for the determination of hydrogen sulfide. Firstly, a functional monomer 3,5-diaminobenzoic acid is employed to modify on the CAU-10-NH₂, the product CAU-10-NH-dAba has strong fluorescent performance at 412 nm under an excitation wavelength of 320 nm. Subsequently, it is further modified by the azide group to form CAU-10-NH-dAba-N₃. This azidation inhibits the fluorescent signal. However, in the presence of hydrogen sulfide, the azide group is specifically reduced to amidogen, and results in the recovery of the fluorescence. The CAU-10-NH-DABA-N₃ was characterized by solid state NMR, XPS, fluorescence, IR, XRD, SEM and specific surface area. After the optimization of pH value, temperature and interaction time, the detection results of hydrogen sulfide demonstrate the linear range of this strategy is from 20 to 140 nM with a detection limit of 1.51 nM, which is significantly better than that of the CAU-10-NH₂ merely modified by 3,5-dinitrobenzoic acid. Meanwhile, the satisfactory assay results of hydrogen sulfide in serum sample and Pearl river water suggest a potential application prospect of this strategy in clinical diagnosis and environment monitoring.

Fabrication of a "turn-on"-type enantioselective fluorescence sensor via a modified achiral MOF: applications for synchronous detection of phenylalaninol enantiomers

Homochiral metal-organic frameworks (HMOFs) have garnered considerable attention due to their extrachiral properties and broad application for chiral recognition. However, assembling a pair of high-quality chiral MOFs for sensing enantiomers precisely is a formidable challenge because of the complicated chiral environment and uncontrollable coordinated conditions. Herein, one pair of homochiral UiO-66 analogues, S-1 (l-AP@UiO-66-(COOH)₂) and R-1 (d-AP@UiO-66-(COOH)₂), are reported for chiral recognition. They were fabricated via a condensation reaction between the carboxyl groups of UiO-66-(COOH)₂ and amino groups of l/d-amino propanol (l/d-AP). These novel fluorescent probes exhibited highly enantioselective fluorescence enhancement towards l/d-phenylalaninol (l/d-PA). For example, when S-1 and R-1 were treated with l-PA or d-PA, they displayed different fluorescence responses: the enantiomeric fluorescence enhancement ratio (ef) was 2.51 and 0.41 for S-1 and R-1, respectively. Hence, a visible difference in fluorescence enhancement for l-PA and d-PA and excellent enantioselective behavior between S-1 and l-PA (or R-1 and d-PA) was displayed. Measurements of fluorescence lifetime, powder X-ray diffraction, molecular-dynamic simulations and Benesi-Hildebrand plots were employed to determine the observed high enantioselectivity for l/d-PA. In brief, we found that two post-modified HMOFs, S-1 and R-1, were outstanding enantioselective sensors for detecting l-PA and d-PA. They had a prominent difference in ef and remarkable enantioselectivity factor α and ΔΔG based on steric hindrance and stereochemical difference.

Three coordination polymers with regulated coordination interactions as fluorescent sensors for monitoring purine metabolite uric acid

A facile optical sensor for uric acid (UA), an early pathological signature for the metabolic function of humans, was developed based on water-stable coordination polymers (CPs). Herein, three new isostructural fluorescent CPs, [Ln(TCPB)(DMF)3]n (Ln = La, CP 1; Ce, CP 2 and Pr, CP 3; H3TCPB = 1,3,5-tris(1-(2-carboxyphenyl)-1H-pyrazol-3-yl)benzene), with various metal ions were solvothermally synthesized. Significantly, by regulating the metal-organic coordination interactions, the fabricated CP 3 can quantitatively recognize UA with higher sensitivity compared with CP 1 and CP 2. The mechanism for the sensing properties further demonstrates the best performance of CP 3 and the excellent selectivity for UA monitoring. This work represents the strategy of designing fluorescent CP sensors to determine UA and provides a convenient approach for developing analysis platforms for the assessment of related disease progress and human health monitoring.