Functionalized Metal-Organic Framework UiO-66-NH-BQB for Selective Detection of Hydrogen Sulfide and Cysteine

A fluorescent sensor based on pentafluoropropanoic acid-functionalized UiO-66-NH2 for enhanced selectivity and sensitivity of dicloran detection

A pentafluoropropionic acid-functionalized fluorescent metal-organic framework material (UiO-66-NH2-PFPA) is prepared by a simple post-synthetic modification (PSM) strategy for the sensitive and selective detection of dichloran (DCN). The results of fluorescence experiments demonstrate that the sensitivity of UiO-66-NH2-PFPA (limit of detection, LOD = 0.478 μM) to DCN is nearly 10.93 times higher than that of UiO-66-NH2 (LOD = 5.225 μM) and the material has good selectivity and anti-interference ability. After the addition of DCN, the blue fluorescence of UiO-66-NH2-PFPA is obviously quenched. Therefore, the possible quenching mechanism is further discussed in combination with relevant experiments and density functional theory calculations. Moreover, the sensor is applied to the detection of DCN in fruit samples with a satisfactory recovery of 101.1-107.9%, which implies that UiO-66-NH2-PFPA is expected to be a candidate material for the detection of DCN in food.

Immobilized Urease Vector System Based on the Dynamic Defect Regeneration Strategy for Efficient Urea Removal

The clearance of urea poses a formidable challenge, and its excessive accumulation can cause various renal diseases. Urease demonstrates remarkable efficacy in eliminating urea, but cannot be reused. This study aimed to develop a composite vector system comprising microcrystalline cellulose (MCC) immobilized with urease and metal-organic framework (MOF) UiO-66-NH2, denoted as MCC@UiO/U, through the dynamic defect generation strategy. By utilizing competitive coordination, effective immobilization of urease into MCC@UiO was achieved for efficient urea removal. Within 2 h, the urea removal efficiency could reach up to 1500 mg/g, surpassing an 80% clearance rate. Furthermore, an 80% clearance rate can also be attained in peritoneal dialyzate from patients. MCC@UiO/U also exhibits an exceptional bioactivity even after undergoing 5 cycles of perfusion, demonstrating remarkable stability and biocompatibility. This innovative approach and methodology provide a novel avenue and a wide range of immobilized enzyme vectors for clinical urea removal and treatment of kidney diseases, presenting immense potential for future clinical applications.

Synergistic synthesis of gold nanoflowers as upconversion near-infrared nanoprobe energy acceptor and recognition unit for improved hydrogen sulfide sensing

A highly sensitive and selective upconversion near-infrared (NIR) fluorescence and colorimetric dual readout hydrogen sulfide (H2S) nanoprobe was constructed based on the excellent NIR fluorescence emission performance of upconversion nanomaterials (UCNPs), the specific recognition effect of synergistically synthesized gold nanoflowers (trypsin-stabled AuNFs (Try-AuNFs)) and the effective NIR fluorescence quenching capability. In this assay, the sensing strategy included three processes. First of all, the synthesized UCNPs can emit 803 nm NIR fluorescence when they were excited by 980 nm excitation light. Secondly, as a result of the principle of fluorescence resonance energy transfer (FRET), Try-AuNFs can effectively quench the NIR fluorescence of UCNPs at 803 nm, which can effectively improve the signal-to-background ratio of nanoprobes, thereby improving the sensitivity of the probes. Thirdly, in the presence of H2S, the Try protective layer on the surface of Try-AuNFs was specifically penetrated, which will subsequently cleave Try-AuNFs via the strong S-Au bond. As such, the NIR fluorescence of UCNPs will be restored, achieving high selectivity and sensitivity detection of H2S. Under optimized conditions, the linear response range of H2S was 0.1-300 μM, and the detection limit was 53 nM. It is worth noting that the Try on the surface of Try-AuNFs via the synergistic effect can increase the steric hindrance of the probe, and this can effectively prevent the interaction between the probe with biothiols (cysteine (Cys), homocysteine (Hcy)) and other natural amino acids (non-thiol-containing) with resultant in the high selectivity regarding the detection of H2S in human serum, which is unlikely to be achieved by AuNFs synthesized by the gold seed method (Se-AuNFs). This work not only provided a new type of UCNPs fluorescence quencher and recognition unit, but also exemplified that the use of the physical properties (steric hindrance) of protein ligands on the surface of nanoflowers can improve the specificity of the probe. This will provide new ideas for the design of other nanoprobes.

Dose-Dependent Effect on Plant Growth of Exposure to Metal-Organic Framework MIL-101(Cr)

With the increasing use of metal-organic frameworks (MOFs), they will inevitably enter the environment intentionally or unintentionally. However, the effects of MOFs on plant growth are poorly understood. Here, we investigated the effects of exposure of the rhizosphere to MOFs on plant growth. MIL-101(Cr) was selected as a research model due to its commercial availability and wide use. Soybean plants at the two-leaf stage were subjected to various durations (1-7 days) and concentrations (0-1000 mg/L) of exposure in hydroculture with a control group treated with ultrapure water. We found that MIL-101(Cr) had a positive effect on soybean growth at a lower dose (i.e., 200 mg/L); however, at higher doses (i.e., 500 and 1000 mg/L), it exhibited significant toxicity to plant growth, which is evidenced by leaf damage. To investigate the mechanism of this effect, we used Cr as an indicator to quantify, track, and image MIL-101(Cr) in the plant with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Results indicated that MIL-101(Cr) primarily accumulated in the cortex of roots (up to 40 times higher than that in stems), with limited translocation to stems and negligible presence in leaves and cotyledons. In addition, metabolomic analysis of soybeans indicated that low-dose MIL-101(Cr) could increase the sucrose content of soybean roots to promote plant growth, while a high dose could induce lipid oxidation in roots. This study provides valuable insights into the ecological toxicology of MOFs and underscores the importance of assessing their environmental impact for sustainable agricultural practices.

Machine Learning System To Monitor Hg2+ and Sulfide Using a Polychromatic Fluorescence-Colorimetric Paper Sensor

An optical monitoring device combining a smartphone with a polychromatic ratiometric fluorescence-colorimetric paper sensor was developed to detect Hg2+ and S2- in water and seafood. This monitoring included the detection of food deterioration and was made possible by processing the sensing data with a machine learning algorithm. The polychromatic fluorescence sensor was composed of blue fluorescent carbon quantum dots (CDs) (BU-CDs) and green and red fluorescent CdZnTe quantum dots (QDs) (named GN-QDs and RD-QDs, respectively). The experimental results and density functional theory (DFT) prove that the incorporation of Zn can improve the stability and quantum yield of CdZnTe QDs. According to the dynamic and static quenching mechanisms, GN-QDs and RD-QDs were quenched by Hg2+ and sulfide, respectively, but BU-CDs were not sensitive to them. The system colors change from green to red to blue as the concentration of the two detectors rises, and the limits of detection (LOD) were 0.002 and 1.488 μM, respectively. Meanwhile, the probe was combined with the hydrogel to construct a visual sensing intelligent test strip, which realized the monitoring of food freshness. In addition, a smartphone device assisted by multiple machine learning methods was used to text Hg2+ and sulfide in real samples. It can be concluded that the fabulous stability, sensitivity, and practicality exhibited by this sensing mechanism give it unlimited potential for assessing the contents of toxic and hazardous substances Hg2+ and sulfide.

A gold-silver bimetallic nanocluster-based fluorescent probe for cysteine detection in milk and apple

Noble metal nanoclusters have attracted much attention due to their excellent optical properties. In the present work, a silver-doped gold-based bimetallic nanoclusters (Au/Ag NCs) were reasonably designed and prepared through a one-pot method by using 5-mercapto-1-tetrazolea-acetic acid sodium salt (MTAS) as a protector and capping agent. In comparison with the monometallic nanoclusters, Ag-doped metallic nanoclusters show better performance. The particle size of the MTAS-Au/Ag NCs is slightly larger than that of the undoped Au NCs by about 1.86 ± 0.5 nm, and the MTAS-Au/Ag NCs exhibit an emission peak at 635 nm with a quantum yield (QY) of 3.05%. The presence of cysteine (Cys) induces efficient quenching of the photoluminescence of the obtained Au/Ag NCs, achieving the sensitive detection of Cys with a detection limit of 16 nM. The fluorescence quenching rate of the nano fluorescent probe has a linear relationship with the cysteine concentration. Under the best detection conditions, the linear range for Cys detection with MTAS-Au/Ag NCs as a probe is 0.05-25.0 μM. Moreover, this probe has been successfully applied to the analysis of Cys in milk and apples, and a satisfactory recovery rate has been obtained, indicating the effectiveness and reliability of the sensor system for the detection of actual samples.

Water-Stable Eu6-Cluster-Based fcu-MOF with Exposed Vinyl Groups for Ratiometric and Fluorescent Visual Sensing of Hydrogen Sulfide

Detection of H₂S in the biological system has attracted enormous attention in recent years. In this work, a new vinyl-functionalized metal-organic framework (MOF), [(Me₂NH₂)₂] [Eu₆(μ₃-OH)₈(BDC-CH═CH₂)₆(H₂O)₆] (Eu-BDC-CH═CH₂, BDC-CH═CH₂ = 2-vinylterephthalic acid), was synthesized under solvothermal conditions. The vinyl groups in the ligands can not only modulate the "antenna effect" of the ligand on Eu³⁺ ions but also serve as an exposed reactive site to allow for the quantitative detection of H₂S by Eu-BDC-CH═CH₂. The ratiometric fluorescent probe has the advantages of water stability, acid-base stability (pH = 2-11), fast response (<2 min), high selectivity, and sensitivity (LOD = 38.4 μM). We also used Eu-BDC-CH═CH₂ to detect and analyze H₂S in tap and lake waters, demonstrating the potential of the probe for biological and environmental applications. In addition, the MOF-based agarose hydrogel film allows for the visual detection of H₂S via a smartphone by identifying the RGB values. The vinyl-functionalized MOF can thus be a powerful sensing platform for H₂S.

Simple Design Concept for Dual-Channel Detection of Ochratoxin A Based on Bifunctional Metal-Organic Framework

A simple fluorescence and electrochemical dual-channel biosensor based on bifunctional Zr(IV)-based metal-organic framework (Zr-MOF) was proposed to detect Ochratoxin A (OTA). The bifunctional Zr-MOF, with photoluminescence properties and enormous electroactive ligands, was exploited to load OTA-specific aptamers for designing signal probes, greatly simplifying the probe-fabrication process and improving sensing reliability. Upon specific recognition of aptamer toward OTA, the anchored probe was released from the sensing interface into the reaction solution. In this circumstance, the increased amount of the signal probe in reaction solution led to an enhanced fluorescence response, while the decreased amount of the signal probe on the sensing interface resulted in a diminished electrochemical response. According to the dual-channel signal change with increasing OTA concentration, the visual fluorescence strategy was established for intuitive OTA detection, and meanwhile, sensitive electrochemical assay with a detection limit of 0.024 pg/mL was also achieved with the help of one-step electrodeposition as a sensing platform. Moreover, the proposed dual-channel assay has been successfully applied to determine OTA levels in corn samples with rapid response, superior accuracy, and high anti-interference capability, providing a promising method for food safety monitoring.

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.

Designed multifunctional ratiometric fluorescent probe for directly detecting fluoride ion/ dichromate and indirectly monitoring urea

UiO-66-NH₂@eosin Y composite was obtained by confining eosin Y (EY) into the cavities of Zr-MOF and could emit two fluorescence peaks at 453 and 543 nm at an excitation wavelength of 355 nm. This multi-responsive and multifunctional ratiometric fluorescent nanoprobe not only enable directly distinct detection of F^-/Cr₂O₇^2- with ultra-high selectivity and sensitivity, but also could indirectly monitor the concentration of urea based on unique enzymatic hydrolysis reaction. The multifunctional probe was utilized for fluorescence labeling F-/Cr₂O₇^2- in sweat latent fingerprint through an environmentally friendly powder strategy and exhibited obvious luminescence visualization changes. Notably, the corresponding portable on-line test strips of probe for detection of F^- and Cr₂O₇^2- were made for monitoring the levels of F^- and Cr₂O₇^2-. Furthermore, the probe was applied to evaluate the degrees of F^-/Cr₂O₇^2- in HepG-2 cell and urea in serum with superior results,which indicate the potential application of the as-synthesized UiO-66-NH₂@EY as multifunctional probe for the detection of F^-, Cr₂O₇^2- and urea in biological samples. Finally, in order to extend the device-based applications of probe, an AND-OR-coupled molecular logic gate was put on agenda.

GaOOH-modified metal-organic frameworks UiO-66-NH2: Selective and sensitive sensing four heavy-metal ions in real wastewater by electrochemical method

Heavy metal pollution in the environment poses a serious threat to the ecosystem and human health, which has attracted widespread attention. In this study, an octahedral structure composite composed of UiO-66-NH₂ MOFs and semiconductor GaOOH materials has been prepared and used as electrode materials successfully. These composites can be used for the real-time and online determination of Cd²⁺, Cu²⁺, Hg²⁺, and Pb²⁺ in real water samples simultaneously or alone via an electrochemical method. Zr-MOF has a large and unique surface area that is beneficial to the adsorption and preconcentration of heavy metal ions. The experiment parameters such as pH, deposition potential, and deposition time were optimized. Under the optimized conditions, the electrochemical performances and practical applications of Zr-MOF composites modified electrode have been investigated, which shows excellent wider linear range and lower detection limit (LOD). The results demonstrated excellent selectivity, reproducibility, stability and applicability for the detection of four metal ions. These superior features stem from the synergistic reaction mechanism of UiO-66-NH₂ and GaOOH. In addition, it has been established a new detection strategy for heavy metal ions through the form of metal-organic framework (MOF) composite in this work. It may provide a novel platform for the quantitative determination of heavy metal ions in various environmental samples.

Chromic and Fluorescence-Responsive Metal-Organic Frameworks Afforded by N-Amination Modification

Sensory materials that show color and/or fluorescence changes in response to specific gases or vapors have important applications in many fields. Here, we report the postsynthetic preparation of novel sensory metal-organic frameworks (MOFs) and their multiple responsive properties. Through postsynthetic N-amination, the 2,2'-bipyridyl spacers in a Zr(IV) MOF are partially transformed into N-aminobipyridinium. The new MOF (Zr-bpy-A) shows chromic behavior toward ammonia and amines because the electron-deficient pyridinium groups form charge-transfer complexes with amino moieties. It also shows a unique chromic response to formaldehyde owing to the Schiff-base condensation with the N-amino groups. Furthermore, the N-amino group can be used to graft different polycyclic aromatic hydrocarbons, which endow the MOF with strong fluorescence of variable colors and afford a high-contrast fluorescence response to ammonia/amines and formaldehyde associated with the chromic response. The presence of the unquaternized bipyridyl group also leads to a fluorescence response to HCl. The multiple responsive behaviors hold appeal for applications in sensing, switching, and antifake marking, which are illustrated with a test paper and writing ink.

Detection of sialic acid using boronic-acid-functionalized metal organic framework UiO-66-NH2@B(OH)2

Sialic acid (SA) is a crucial component of glycoproteins and glycolipids on the cellular membrane, which is essential for maintaining the function of cell membranes, such as cell recognition and communication. Simultaneously, sialic acid plays a significant role in many physiological and pathological processes. Hence, it is urgent to develop a simple and sensitive strategy for determining sialic acid. In this work, a new metal-organic framework called UiO-66-NH₂@B(OH)₂ has been designed and synthesized for the recognition and detection of sialic acid. The boronic acid functional group in UiO-66-NH₂@B(OH)₂ can bind to a diol moiety of the glycerol side chain of sialic acid, which will attenuate or even quench the fluorescence of UiO-66-NH₂@B(OH)₂, thus opening a new road to detect sialic acid. Based on the measurement results, sialic acid can be quantitatively measured in a linear range of 0.05-2.5 mmoL/L with the UiO-66-NH₂@B(OH)₂ probe. The detection limit of sialic acid is as low as 0.025 mmol/L. Furthermore, the boronic-acid functionalized probe UiO-66-NH₂@B(OH)₂ displays high sensitivity and high selectivity to recognize the sialic acid in mouse serum samples. Therefore, the developed UiO-66-NH₂@B(OH)₂ can be used as a promising probe to identify and detect sialic acid in the practical application.

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.

Covalently immobilize crude d-amino acid transaminase onto UiO-66-NH2 surface for d-Ala biosynthesis

Enzyme reaction has been accepted widely in numerous applications owing to the high efficiency and stereo-selectivity, as well as simple preparation by gene engineering. However, the fragility and complex purification process of the enzyme are long-standing problems which limit the large-scale application. One possible solution may be the enzyme immobilization. As one type of porous material with high loading capacity and designable functionality, Metal-Organic Frameworks (MOFs) are ideal choices for the immobilization of enzyme with a considerable interest in recent years. In this study, d-amino acid transaminase (DAT), an important enzyme for industrial synthesis of d-Ala, was covalently immobilized on the surface of a star MOFs material, UiO-66-NH_2. Interestingly, we found that the nanoscale hybrid enzyme UiO-66-NH₂-Gd-DAT not only maintained the high catalytic efficiency but also got rid of the interference of polluting enzymes, which meant that we could obtain efficient and stereo-selective immobilized enzyme without complex purification process. In general, our findings demonstrated that using UiO-66-NH₂ might be a promising strategy to immobilize enzyme and produce effective biocatalyst with high activity and stereo-selectivity.

UiO series of metal-organic frameworks composites as advanced sorbents for the removal of heavy metal ions: Synthesis, applications and adsorption mechanism

Heavy metal pollution has threatened the ecological environment and human health, therefore, effective removal of these toxic pollutants from various complex substrates is of great significance. So far, adsorption is still one of the most effective approaches. Metal-organic frameworks (MOFs), which are porous crystalline materials consisting of metal ions or metal clusters and organic ligands through coordination bonds. Due to their high surface area, porosity, as well as good chemical/thermal stability, the materials have recently attracted great attention in environmental analytical chemistry. This review mainly focused on the recent studies about the applications of UiO series MOFs and their composites as the emerging MOFs, which have been used effectively for the adsorption and removal of diverse heavy metal ions from a variety of environmental samples as novel adsorption materials. Moreover, an elaboration about UiO-MOFs and its composites including the synthetic methods and the applications of these materials in the removal of heavy metal ions were presented in detail. In addition, the adsorption characteristics and mechanism of UiO-MOFs as solid sorbents for heavy metal ions were discussed, including adsorption isotherms equation, adsorption thermodynamics, and kinetics. To this end, the developing trends of MOF-based composites for the removal of heavy metal ions had also prospected. This review will provide a new idea for the study of the adsorption mechanism of heavy metal ions on sorbents and the development of high-performance media for the efficient removal of pollutants in wastewater.

Zirconium(Ⅳ)-based metal-organic framework for determination of imidacloprid and thiamethoxam pesticides from fruits by UPLC-MS/MS

Zirconium(Ⅳ)-based metal-organic framework (MOF)-UiO-66-NH₂ was fabricated to adsorb the imidacloprid and thiamethoxam in fruit samples before analysis using UPLC-MS/MS. The UiO-66-NH₂ was confirmed by SEM, FTIR, and XRD. Key experimental parameters were investigated by response surface methodology (RSM). The desirability recovery of imidacloprid was 94.52% under optimum conditions (mount of adsorbent = 52.48 mg, volume of eluent = 5.18 mL, pH = 9, extraction time = 15 min). The desirability recovery of thiamethoxam was 93.57% under optimum conditions (mount of adsorbent = 50.58 mg, volume of eluent = 2.6 mL, pH = 5.65, extraction time = 11.94 min). Under the optimal conditions, the actual recovery of imidacloprid and thiamethoxam was 92.39% and 94.37%, respectively. Besides, the method was applied successfully to detect imidacloprid and thiamethoxam in different fruit samples. The results demonstrated that the UiO-66-NH₂ is an excellent adsorbent for the extraction imidacloprid and thiamethoxam from fruit samples.

Carbon dots based ratiometric fluorescent sensing platform for food safety

Food safety has become a major global concern and the rapid detection of food nutritional ingredients and contaminants has aroused much more attention. Nanomaterials-based fluorescent sensing holds great potential in designing highly sensitive and selective detection strategies for food safety analysis. Carbon dots (CDs) possess tremendous prospects in fluorescent sensing food ingredients and contaminants due to their superior properties of chemical and photostability, highly fluorescence with tunability, and no/low-toxicity. Numerous endeavors are demanded to contribute to overcoming the challenge of lower sensitivity and selectivity of the sensors interfered by various components in intricate food matrices to ensure food safety and human health. Nanohybrid CDs based ratiometric fluorescent sensing with self-calibration is regarded as an efficient strategy for the CDs based sensors for the specific recognition of target analyte in the food matrices. This work is devoted to reviewing the development of nanohybrid CDs based ratiometric fluorescent sensing platform and the perspectives of the platform for food safety. The applications of nanohybrid CDs in sensing are summarized and the sensing mechanisms are briefly discussed.