Tactile Sensors: Hydroxyl Decorated Silver Metal-Organic Frameworks for Detecting Cr2O72-, MnO4-, Humic Acid, and Fe3+ Ions

Tri-emissive red-green dye-encapsulated UiO-66-Ph as a white-light emission fluorescence sensor for Fe3+ and Cr2O72- detection in environmental water samples

Excessive inorganic ions in water sources can accumulate abnormally or be deficient in the human body, leading to serious health risks, such as liver and kidney damage or even cancer. Therefore, efficient and accurate detection of excessive inorganic ions in water is urgently needed. Using an in situ encapsulation method under solvothermal conditions, we develop a series of triple-emission fluorescent sensors, C6&RhB@UiO-66-Ph (C&R@U), by encapsulating green-emitting Coumarin 6 (C6) and red-emitting Rhodamine B (RhB) into a blue-emitting UiO-66-Ph MOF with 1,4-H2NDC as the ligand. Among them, C&R@U3 exhibits white-light emission with a CIE coordinate of (0.32, 0.32) and is used for the detection of Fe3+ ions and Cr2O72- ions in water. When the C&R@U3 fluorescent probe interacts with target ions, the three emission peaks of the probe are quenched due to the resonance energy transfer effect, resulting in significant shifts in its CIE coordinates compared to other ions. The fluorescence intensity of the C&R@U3 probe demonstrates excellent linearity with Fe3+ ion concentrations (0-0.6 mM) and Cr2O72- ion concentrations (0-0.1 mM), with detection limits of 0.71 μM and 16.9 nM, respectively. Experiments with real-world water samples and portable fluorescence test papers validate the practical applicability of C&R@U3, revealing its great potential in on-site inorganic ion detection. This work provides experimental basis and theoretical foundation for the development of new multifunctional fluorescent sensors, promoting the application of MOFs in environmental monitoring.

Zn-Based Three-Dimensional Metal-Organic Framework for Selective Fluorescence Detection in Zwitterionic Ions

Zinc-based MOFs exhibit significant advantages in ion detection due to their unique structure and chemical properties. They can efficiently and selectively recognize and detect specific ions, making them powerful analytical tools for applications in environmental monitoring, biomedical fields, and more. In this work, we used a simple ligand to improve the coordination environment of Zn2+ ions and successfully synthesized a 3D coordination compound Zn(all-bdc)(Py) MOF through a straightforward hydrothermal method at low temperature. Additionally, we explored the potential of this MOF as a bifunctional ion fluorescence probe for both cationic and anionic recognition. The results showed that this 3D porous MOF exhibited excellent recognition ability for trivalent iron ions (Fe3+) and potassium permanganate (KMnO4-) ions due to its highly porous structures and efficient ion recognition. When iron ions were added to 500 μL and potassium permanganate ions were added to 100 μL, the fluorescence of the compound was effectively quenched, and the detection limits for these two ions were 0.95 μM and 0.13 μM, respectively. The mixed-ion experiments also demonstrated that even in the presence of similar ions, this 3D MOF still maintained good selective recognition ability, specifically identifying Fe3+ and KMnO4- ions. This work provides a novel synthetic strategy for the design of MOFs capable of mixed-ion recognition and detection, expanding their application potential in ion sensing and analysis.

Stable Interpenetrated Zirconium-Based Metal-Organic Framework for the Fluorescence Detection of MnO4. Inorg Chem 2025;64:6648-6655. [PMID: 40128184 DOI: 10.1021/acs.inorgchem.5c00200] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

In this work, a novel stable zirconium-based metal-organic framework (Zr-MOF) with the formula [Zr6O4(OH)4(PVDC)6]4·66DMF (Zr-1, H2PVDC = (E,E)-2,5-dimethoxy-1,4-bis[2-(4-carboxylatestyryl)]benzene; DMF = N,N-dimethylformamide) was synthesized by introducing a linear phenylenevinylene-based carboxylate ligand to react with ZrCl4 under solvothermal conditions. According to single-crystal X-ray diffraction measurement, complex Zr-1 featured a 2-fold interpenetrated framework, in which the single coordination framework possessed a structure similar to that of the well-known Zr-MOF, UiO-66, constructed from [Zr6O4(OH)4]12+ clusters and carboxylate ligands PVDC2-. Due to the introduction of the phenylenevinylene-functionalized ligand, complex Zr-1 exhibited a unique fluorescence sensing performance toward permanganate (MnO4-) with different concentrations. At low concentrations, the fluorescence emission intensity of Zr-1 around 510 nm was enhanced significantly with an increase in the concentration of MnO4- in an aqueous suspension. However, while excess MnO4- was added into the suspension, the fluorescence emission intensity decreased significantly, and the single emission peak turned into five emission peaks upon the addition of MnO4-. Such a phenomenon has been scarcely reported in previous MOF-based fluorescence sensors. Moreover, complex Zr-1 showed high anti-interference capability for the detection of MnO4- both at low and high concentrations. This work may pave a new way for the development of MOF-based fluorescence sensing platforms.

Luminescent Metal-Organic Framework with Negative Electrostatic Pores for Highly Selective GDP Sensing

Electrostatic potential (ESP) plays an essential role in studying interactions among molecules. Developing probe materials capable of selectively detecting analytes by aligning their molecular ESP with the electrostatic interaction of the host probe material is critically important for identifying analogous analytes; however, relevant research is extremely lacking. In this work, we synthesized a luminescent metal-organic framework (LMOF, Cd-DBDP) featuring negative electrostatic pore environments achieved by incorporating numerous electronegative oxygen atoms and N-containing aromatic rings from organic linkers. The molecular ESP distributions of Cd-DBDP and RNA-related nucleotides were calculated and employed to predict the sensing results. Fluorescence tests demonstrated that Cd-DBDP represents the first example of an MOF-based sensor for guanosine diphosphate (GDP) sensing, and the experimental observations were highly consistent with the theoretical prediction. The sensing mechanism for GDP was thoroughly studied through Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), X-ray photoelectron spectroscopy (XPS), and theoretical calculations. These findings provide valuable insights into understanding the interplay between the molecular ESP distribution condition and the sensing results. This study offers a theoretical guide for future sensory research and provides effective means for the design and synthesis of highly efficient sensing MOFs, lending a solid groundwork for further exploration in this field.

Single-phase dye-embedded triple-emitting EY&BPEA@Zr-MOFs for selective detection of inorganic ions in environmental water

The synthesis of multi-wavelength emission fluorescent metal-organic framework sensors has received widespread attention in recent years. Under solvothermal conditions, a series of triple-emission fluorescent sensors were fabricated by in situ encapsulation of red emitting Eosin Y and green emitting 9,10-bis(phenylethynyl)anthracene (BPEA) into a blue emitting naphthalene-based Zr-MOF. By combining the dye quantity regulation and the resonance energy transfer between MOFs and dyes, the single-phase EY&BPEA@Zr-MOFs exhibited tunable triple-emission fluorescence. The EY&BPEA@Zr-MOFs presented the ability to selectively detect Cr2O72- ions and Fe3+ ions in aqueous solution by means of fluorescence quenching and changes in color coordinates. Mechanistic studies revealed that the main mechanism for detecting Cr2O72- and Fe3+ ions involves a cooperative interplay between electron transfer and fluorescence resonance energy transfer between MOFs and analytes. The detection experiments conducted with real-world water samples and the portable fluorescence test papers, conclusively validated the practical applicability of EY&BPEA@Zr-MOFs.

An economical luminescent film sensor for rapid detection of permanganate in water and Diquat in wheat, apple and Chinese cabbage

Developing portable devices with reliable and swift luminescent responses for the detection of anions and pesticide residues are extremely expected for the foods safety and sequently the public health. To reduce cost and simplify the preparation and detection process, a new highly luminescent lanthanide species, [TbL(NO3)3]·0.5CH3CN (TbL) based on an amido-armed open chain crown ether (L) was prepared and well characterized for the assembly of hybrid film, TbL@PMMA. Expectedly, TbL@PMMA exhibits excellent sensitivity and selectivity toward MnO4- and diquat (DQ) rapidly in water with quite low detection limits of 0.53 μM and 0.094 μM respectively. Moreover, TbL@PMMA can also be applicable to MnO4- detection in real water as well as DQ detection in wheat, apples, Chinese cabbage and real water effectively. The recognition mechanisms were explored in detail both experimentally and theoretically. Our research is valuable for the development of new sensing materials for application in food and environmental safety.

Chalcone-based Turn-Off Chemosensor for Selective and Susceptible Detection of Fe2+ Ions: Spectroscopic and DFT Investigations

Herein, in this report we are introducing newly synthesized chalcone derivative, "(E)-1-phenyl-3-(4-((5-(((Z)-thiophen-2-ylmethylene)amino)-1,3,4-thiadiazol-2-yl)thio)phenyl)prop-2-en-1-one" (5), as a chemosensor to detect Fe2+ metal ions in HEPES buffer solution of pH 7.5. Spectroscopic techniques were used to confirm the synthesized sensor. To determine the chemical reactivity and molecular stability of the probe, a frontier molecular orbitals investigation was carried out. A molecular electrostatic potential map was investigated to know the binding site of 5 for metal ion coordination. The theoretical absorption and fluorescence emission properties were estimated and correlated with the experimental observations. The sensor showed excellent selectivity for Fe2+ compared to all other studied metal ions. The fluorescence binding studies were carried out by adding different amounts of Fe2+ ions for a fixed concentration of probe 5. The inclusion of Fe2+ ions resulted in a decrease in fluorescence intensity with a bathochromic shift of emission wavelength of 5 due to the 5-Fe2+ complexation. The binding affinity value for the probe was found to be 576.2 M-1 with the help of the Stern-Volmer plot. The Job's plot and mass spectra supported the 2:1 (5: Fe2+) stoichiometry of complex formation. The detection limit and limit of quantification of 5 for Fe2+ were calculated to be 4.79 × 10-5 M and 14.54 × 10-5 M. Further, in addition to this, the photophysical parameters such as fluorescence lifetime of 5 and 5-Fe2+ complex measured to be 0.1439 and 0.1574 ns. The quantum yield of 5 and 5-Fe2+ was found to be 0.0398 and 0.0376. All these experimental findings revealed that probe 5 has excellent selectivity and sensitivity for Fe2+ ions.

Copper-based metal-organic frameworks for antitumor application

It is urgent to exploit multifunctional materials and combined approaches for efficient antitumor effects. Copper-based metal-organic frameworks (Cu-MOFs) have excellent performances in catalysis, biocompatibility, photothermal conversion, and regulate metabolism, which make them attract more and more attention in antitumor application. Therefore, in this review, representative ligands, synthetic methods, antitumor mechanism, and antitumor applications of Cu-MOFs were provided. Special emphasis is placed on the recent antitumor applications of Cu-MOFs in drug carriers, antitumor therapy, tumor imaging, and theranostic, which are summarized with examples. Finally, we presented the dilemma faced by Cu-MOFs and offered a new perspective for future antitumor application. Hopefully, this review may serve as a reference for further development and application of Cu-MOFs.

Lanthanide-Porphyrin MOF as a Multifunctional Platform for Detection and Integrated Elimination of Cr(VI) and Ciprofloxacin

Environmental concerns are driving the development of eco-friendly and effective methods for contaminant monitoring and remediation. In this study, a lanthanide porphyrin-based MOF with dual fluorescence sensing and photocatalytic properties was synthesized and applied for the detection and combined removal of Cr(VI) and ciprofloxacin (CIP). Using different excitation wavelengths, the material exhibited selective detection of Cr(VI) via fluorescence quenching and CIP through fluorescence enhancement. The variation in color intensity of Tb-MOF on 3D EEM spectra enabled simultaneous detection of both contaminants. Additionally, Tb-MOF demonstrated a synergistic removal effect, achieving over 95% removal rates of Cr(VI) and CIP within 90 min, with consistent sensing and catalytic performance across four cycles. Mechanistic investigations revealed that (i) strong coordination between Tb3+ and CIP altered the surface potential of Tb-MOF, enhancing Cr(VI) adsorption; (ii) as an efficient electron acceptor, Cr(VI) promoted electron transfer and its reduction to Cr(III); and (iii) superoxide radicals generated via a type I mechanism played a key role in CIP degradation. This research underscores the potential of Tb-MOF as a multifunctional platform for simultaneous detection and synergistic remediation of mixed pollutants.

Study curing of epoxy resin by Isophoronediamine/ Triethylenetetramine and reinforced with montmorillonite and effect on compressive strength

Epoxy is a widely used thermosetting resin recognized for its exceptional performance in adhesives, coatings, and various other applications, attributed to its high tensile strength, stiffness, electrical performance, and chemical resistance. Epoxy-clay nanocomposites are extensively employed across diverse industries. The physical and chemical properties of these nanocomposites are influenced by the processing methods, clay modifiers, and curing agents used during their preparation. In this study, epoxy/nanoclay composites based on Diglycidyl Ether Bisphenol-A (DGEBA) will be cross-linked using Isophorone Diamine (IPD), a cycloaliphatic amine, and Triethylenetetramine (TETA), a linear aliphatic amine. The initial phase of the research will assess the impact of different types of cross-linkers, both individually and in combination at various molar ratios (such as Isophorone Diamine: Triethylenetetramine (IPA: TETA) / 25:75 and 75:25), on the compressive strength of the epoxy mortar. In the subsequent phase, the epoxy formulation with an Isophorone Diamine: Triethylenetetramine (IPD: TETA / 75:25), which demonstrates the highest compressive strength, will be selected for further investigation. This formulation will be used to evaluate the effects of different weight percentages (3%, 5%, and 7%) of organically modified montmorillonite (OMMT). The prepared epoxy composites will be characterized using a range of techniques, including Fourier Transform Infrared Spectroscopy (FT-IR), Transmission Electron Microscopy (TEM), and Scanning Electron Microscopy (SEM). The epoxy/nanoclay composite with an IPD: TETA / 75:25 and 3 wt % OMMT is expected to show the highest compressive strength, which is 94 MPa.

Fluorescence Naphthalene Cationic Schiff Base Reusable Paper as a Sensitive and Selective for Heavy Metals Cations Sensor: RSM, Optimization, and DFT Modelling

Heavy metals are particularly damaging contaminants in the environment, and even trace concentrations represent a risk to human health due to their toxicity. To detect the heavy metals of Mn2+ and Co2+ ions, a novel selective reusable paper-based Fluorescence naked-eye sensor based on naphthalene cationic Schiff base (NCSB) was synthesized and confirmed using FT-IR, 1 H-NMR, and MS tools. Based on a blue to colorless color change in the aqueous solution, the NCSB sensor is utilized to Mn2+ and Co2+ cations selectively among other metal ions (Fe2+, Cu2+, Mg2+, Ni2+, Zn2+, Cd2+, Hg2+, Pb2+, Sn2+ and Cr3+). In the aqueous medium, the NCSB sensor displayed high sensitivity, with limits of detection (LOD) values of 0.014 µM (14.08 nM) and 0.041 µM (41.47 nM) for Mn2+ and Co2+ cations, respectively. The paper-based sensor naked-eye detected Mn2+ and Co2+ cations in water at concentrations as low as 0.65 µM (65 nM) and 0.086 µM (86 nM), respectively. It was discovered that 5 min of incubation time and a pH range of 7 to 11 were optimal for the complexation reaction between the Mn2+ and Co2+ ions and the NCSB sensor. Through a static quenching process, the interaction of the different metal ions with the Schiff base group in the NCSB molecule results in the development of a ground-state non-fluorescent complex. NCSB sensor was also successfully applied in analysis of Mn2+ and Co2+ in environmental water with good recoveries of 94.8-105.9%. The theoretical calculations based on density functional theory (DFT) studies are in support of experimental interpretations. The links between the input factors and the anticipated response were evaluated using the quadratic model of the response surface methodology (RSM) modeling.

Recent and emerging trends of metal-organic frameworks (MOFs)-based sensors for detecting food contaminants: A critical and comprehensive review

Interest in the use of sensors based on metal-organic frameworks (MOFs) to detect food pollutants has been growing recently due to the desirable characteristics of MOFs, including uniform structures, large surface area, ultrahigh porosity and easy-to-functionalize surface. Fundamentally, this review offers an excellent solution using MOFs-based sensors (e.g., fluorescent, electrochemical, electrochemiluminescence, surface-enhanced Raman spectroscopy, and colorimetric sensors) to detect food contaminants such as pesticide residues, mycotoxins, antibiotics, food additives, and other hazardous candidates. More importantly, their application scenarios and advantages in food detection are also introduced in more detail. Therefore, this systematic review analyzes detection limits, linear ranges, the role of functionalities, and immobilized nanoparticles utilized in preparing MOFs-based sensors. Additionally, the main limitations of each sensing type, along with the enhancement mechanisms of MOFs in addressing efficient sensing are discussed. Finally, the limitations and potential trends of MOFs-based materials in food contaminant detection are also highlighted.

Biocompatible hydrophobic cross-linked cyclodextrin-based metal-organic framework as quercetin nanocarrier for enhancing stability and controlled release

Cyclodextrin-based metal-organic framework (CD-MOF) has been widely used in various delivery systems due to its excellent edibility and high drug loading capacity. However, its typically bulky size and high brittleness in aqueous solutions pose significant challenges for practical applications. Here, we proposed an ultrasonic-assisted method for rapid synthesis of uniformly-sized nanoscale CD-MOF, followed by its hydrophobic modification through ester bond cross-linking (Nano-CMOF). Proper ultrasound treatment effectively reduced particle size to nanoscale (393.14 nm). Notably, carbonate ester cross-linking method significantly improved water stability without altering its cubic shape and high porosity (1.3 cm3/g), resulting in a retention rate exceeding 90% in various media. Furthermore, the loading of quercetin did not disrupt cubic structure and showcased remarkable storage stability. Nano-CMOF achieved controlled release of quercetin in both aqueous environments and digestion. Additionally, Nano-CMOF demonstrated exceptional antioxidant (free radical scavenging 82.27%) and biocompatibility, indicating its significant potential as novel nutritional delivery systems in food and biomedical fields.

Efficient synthesis of benzoacridines and indenoquinolines catalyzed by acidic magnetic dendrimer

A novel solid acid catalyst with recoverability, named as Fe3O4@SiO2@TAD-G2-SO3H, was successfully synthesized by immobilizing sulfonic acid groups on triazine dendrimer-modified magnetic nanoparticles. This nanomaterial structure and composition were thoroughly characterized using various analytical techniques, including thermogravimetric analysis (TGA), elemental analysis, Fourier transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDX), elemental mapping, acid-base titration, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The acid-decorated magnetic dendrimer was served as a highly effective catalyst for the synthesis of tetrahydrobenzo[c]acridin-8(9H)-one and benzo[h]indeno[1,2-b]quinoline-8-one derivatives. The reaction proceeded smoothly under mild conditions through the one-pot condensation of aromatic aldehydes, 1-naphthylamine, and either dimedone or 1,3-indanedione, affording the desired products in high yields ranging from 90 to 96%. The catalyst was easily separated from the reaction mixture by employing a magnetic field, allowing for its recycling up to five times with slight loss in its activity (only 10%). Nearly, quantitative recovery of catalyst (up to 95%) could be obtained from each run. So, this catalyst facilitates the reaction progress and simplifies the purification process. Other remarkable features of this method are operational simplicity, excellent yields, mild condition, and a wide range of substrate applicability.

One master and two servants: One Zr(Ⅳ) with two ligands of TCPP and NH2-BDC form the MOF as the electrochemiluminescence emitter for the biosensing application

Here we put forward an innovative "one master and two servants" strategy for enhancing the ECL performance. A novel ECL luminophore named Zr-TCPP/NH2-BDC (TCPP@UiO-66-NH2) was synthesized by self-assembly of meso-tetra(4-carboxyphenyl)porphine (TCPP) and 4-aminobenzoic acid (NH2-BDC) with Zr clusters. TCPP@UiO-66-NH2 has a porous structure and a highly ordered structure, which allows the molecular motion of TCPP to be effectively confined, thereby inhibiting nonradiative energy transfer. Importantly, TCPP@UiO-66-NH2 has a higher and more stable ECL signal. To further improve the sensitivity of the sensor, we use polydopamine-coated manganese dioxide (PDA@MnO2), which has a double quenching effect, as the quencher. The nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2-N) is one of the ideal markers for the early diagnosis of COVID-19, and its sensitivity detection is of great significance for the prevention and treatment of COVID-19. Thus, we constructed a quenching-type ECL sensor for the ultrasensitive detection of the SARS-CoV-2-N. Its linear range is 10 fg/mL∼1 μg/mL and the calculated detection limit is 1.4 fg/mL (S/N = 3). The spiked recoveries are 97.40-103.8%, with the relative standard deviations (RSD) under 3.0%. More importantly, the technique offers a viable way to identify and diagnose viral infections early.

Progress and prospects in flexible tactile sensors

Flexible tactile sensors have the advantages of large deformation detection, high fault tolerance, and excellent conformability, which enable conformal integration onto the complex surface of human skin for long-term bio-signal monitoring. The breakthrough of flexible tactile sensors rather than conventional tactile sensors greatly expanded application scenarios. Flexible tactile sensors are applied in fields including not only intelligent wearable devices for gaming but also electronic skins, disease diagnosis devices, health monitoring devices, intelligent neck pillows, and intelligent massage devices in the medical field; intelligent bracelets and metaverse gloves in the consumer field; as well as even brain-computer interfaces. Therefore, it is necessary to provide an overview of the current technological level and future development of flexible tactile sensors to ease and expedite their deployment and to make the critical transition from the laboratory to the market. This paper discusses the materials and preparation technologies of flexible tactile sensors, summarizing various applications in human signal monitoring, robotic tactile sensing, and human-machine interaction. Finally, the current challenges on flexible tactile sensors are also briefly discussed, providing some prospects for future directions.