MOF-based Sensor Research Articles

Rational design of a functionalized aluminum metal-organic framework as a turn-off fluorescence sensor for α-ketoglutaric acid.

A 3D metal-organic framework (MOF) called Al-DUT-5-N2H3 (1) (DUT: Dresden University of Technology) was prepared hydrothermally using Al(iii) salt and a hydrazinyl functionalized linker called 2-hydrazinyl-[1,1'-biphenyl]-4,4'-dicarboxylic acid (BPDC-N2H3). Material 1 was successfully characterized by X-ray powder diffraction (XRPD), FT-IR spectroscopy, N2 sorption (BET) experiment, thermogravimetric analysis (TGA), EDX and FE-SEM analyses. The activated form of material 1 (called 1') was achieved by a direct heating process. Material 1' was successfully employed for the solution-phase fluorescence detection of α-ketoglutaric acid (α-KG). It showed high detection performance even when there were other competitive analytes present in the mixture. Material 1' is the first MOF-based fluorescent turn-off sensor for the detection of α-KG. The response time for α-KG is exceptionally low (60 s) as compared to any other reported α-KG sensor. The limit of detection (LOD) was found to be 0.61 μM, which is far better as compared to any other reported sensor for α-KG to date. The mechanism for α-KG sensing was thoroughly investigated and proposed to be PET (photoinduced electron transfer) process by TD-DFT (time-dependent DFT) calculations.

Double-Color Lanthanide Metal-Organic Framework Based Logic Device and Visual Ratiometric Fluorescence Water Microsensor for Solid Pharmaceuticals.

Water is one of the most widespread impurities and contaminants for pharmaceuticals and chemical products. A simple, fast and reliable water assay method is of high significance for the pharmaceutical and chemical manufacturing industries. In this work, lanthanide metal-organic framework Eu-dipicolinic acid/2-aminophthalic acid (Eu-DPA/PTA-NH2) was prepared as a double-color ratiometric fluorescent water sensor, which shows ultrasensitive (limit of detection 0.01% v/v) and linear broad-range (0-100% v/v) response to water. An innovative analytical device based on a one-to-two logic gate was constructed by using the water content and the two fluorescence responses as the input and output signals, respectively. The direct analysis of water content can be achieved by the four output types, NOT (0, 1), PASS 0 (0, 0), PASS 1 (1, 1), and YES (1, 0). Importantly, the metal-organic framework (MOF)-loaded fiber paper was prepared as a microsensor, and a water assay tube was designed for rapid water detection of solid pharmaceuticals via ratiometric chromaticity, coupled with a portable visual determination device. The paper-based microsensor is response-rapid (20 s), long-term stable (at least 30 days), and can achieve the accurate (relative error <9.8%) visual assay of trace water in solid pharmaceuticals. To our knowledge, this is the first time to report an MOF-based double-color ratiometric fluorescent water sensor, a water analytical logic device, and a paper-based water microsensor for point-of-care visual water assay in solid samples via ratiometric chromaticity.

UiO-68-PT MOF-Based Sensor and Its Mixed Matrix Membrane for Detection of HClO in Water.

As an important type of reactive oxygen species (ROS), hypochloric acid (HClO) is closely linked with our daily life, and its convenient and rapid detection is very significant and imperative. Fluorescent and visual probes are being recognized as powerful and convenient tools for detection of ROS in the environment and living organisms by visualizing and imaging. In this contribution, a new metal-organic framework-based fluorescent probe UiO-68-PT, which was generated from a phenthiazine-decorated benzimidazole bridging dicarboxyl ligand and ZrCl4 under solvothermal conditions via in situ one-pot approach, is reported. The obtained UiO-68-PT features a unique HClO and Vitamin C-triggered reversible redox process, which is accompanied by both visual and fluorescence changes. Therefore, it can be a highly sensitive, specific, and reusable sensor to detect HClO species in water via both visual and fluorogenic observation (turn-on). Furthermore, its mixed membrane material (MMM) was fabricated by the combination of UiO-68-PT and poly(vinyl alcohol), and the obtained hydrophilic MMM can be used as a reversible colorimetric card for visual detection of the HClO in aqueous solution.

Bimetal-organic framework nanocomposite based point-of-care visual ratiometric fluorescence pH microsensor for strong acidity

pH is of great importance in understanding physiological and pathologic processes. Abnormal gastric juice pH is an indicator of many gastric diseases such as peptic ulcer and gastric cancer. In this work, a nanocomposite 1-hydroxypyrene@ Co/Tb- dipicolinic acid metal-organic framework (1-OHP@Co/Tb-DPA MOF) was constructed as a ratiometric fluorescent pH sensor for strong acidity. The nanocomposite-based pH sensor was response-rapid (30 s), linearly responsive in the broad pH range of 0.3–7.8 (r > 0.95) and ultra-sensitive in the pH range of 0.3–5.0. Importantly, the nanocomposite-loaded fiber paper was prepared as a visual microsensor for point-of-care pH detection via ratiometric chromaticity, coupled with a homemade portable determination device. The paper-based visual microsensor is response-rapid and sensitive, long-term stable (at least 30 days), and suitable for pH assay of microvolume (as little as 5 μL) samples at pH 0.3–5.0. Both the nanocomposite-based ratiometric fluorescent sensor and the paper-based visual microsensor can accurately determine the pH of artificial gastric juices (relative error <5.4%). To our knowledge, this is the first time to report a MOF-based ratiometric fluorescent pH sensor for strong acidity (pH<1) and a paper-based pH microsensor for point-of-care visual assay via ratiometric chromaticity.

Highly selective detection of Fe3+, Cd2+ and CH2Cl2 based on a fluorescent Zn-MOF with azine-decorated pores

The design and synthesis of sensitive and selective luminescent materials as chemical sensing agents is a fundamental goal in fluorescence assays. Considering high porosity, large surface area, excellent photoluminescence property of metal-organic frameworks (MOFs), luminescent properties of a microporous azine-functionalized MOF, TMU-16, dispersed in different metal ions and solvents have been investigated systematically. The TMU-16 displays superb luminescence emission, and it can detect Fe(III) and Cd(II) ions with high selectivity, excellent sensitivity, and short response time (<1 min). The emission intensities of TMU-16 were quenched upon the addition of Fe3+ and increased upon the addition of Cd2+. The detection limits of TMU-16 for Fe3+/Cd2+ in DMF are estimated to be 0.2 and 0.5 μM, respectively. The effect of other metal ions on the fluorescence intensity of the MOF was also studied and other metal ions showed low interference response in recognition of Fe3+ and Cd2+. Furthermore, TMU-16 exhibits distinct solvent-dependent luminescent spectra with emission intensity significantly enhanced toward dichloromethane. More importantly, this is the first example of MOF-based luminescent sensor as efficient multifunctional fluorescence material which can use for selective sensing of Fe(III) and Cd(II) ions and small molecules such as CH2Cl2.

Stable Lanthanide-Organic Framework as a Luminescent Probe To Detect Both Histidine and Aspartic Acid in Water.

A three-dimensional metal-organic framework (MOF) {[Eu(L)(H2O)2]·DMF} n (1) (H3L = 2'-nitro-3,4',5-biphenyl tricarboxylic acid) was obtained by hydrothermal methods and was characterized in detail. Compound 1 contains [Eu2] binuclear units, and [Eu2] units are further linked by H3L, forming a three-dimensional structure. Stability tests suggest that compound 1 exhibits high solvent, pH, and thermal stability. Besides, we also explored the influence of pH values in the luminescence emission of 1 which shows that pH has a negligible effect on the luminescence intensity with the range of pH = 3-11. Importantly, luminescent investigations reveal that 1 can selectively detect aspartic acid or histidine among 14 amino acids with good regenerability in water. Meanwhile, the concentration of aspartic acid can be quantitatively determined. We also discuss the mechanism of luminescence quenching and enhancement in detail. Importantly, this Eu-MOF provides a MOF-based luminescence sensor to detect two amino acids for the first time.

A ZnII-Based Metal-Organic Framework with a Rare tcj Topology as a Turn-On Fluorescent Sensor for Acetylacetone.

A ZnII-based metal-organic framework (MOF) with a rare tcj topology has been solvothermally synthesized and displays relatively good thermal and chemical stabilities. Interestingly, the MOF can sensitively and selectively sense acetylacetone (acac) via a fluorescence enhancement effect with a detection limit of 0.10 ppm and good reusability, which demonstrates the first example of a MOF-based turn-on fluorescent sensor for acac.

Determination of Malachite Green in Fish by a Modified MOF-Based Electrochemical Sensor

Cu-based metal-organic frameworks modified by silver (Ag/Cu-MOFs) were in situ fabricated through a one-step direct synthesis. The as-prepared mixed-node MOFs were modified on glassy carbon (GC) electrode, which was utilized as a voltammetric sensor for probing malachite green. Compared with the bare GC electrode, the introduced Ag/Cu-MOF film on the electrode surface dramatically improved the sensitivity of the sensor response according to the accumulation and catalytic activity of Ag/Cu-MOFs for malachite green. The developed electrochemical sensor exhibited a low detection limit of 2.2 nM with a wide linear range of 10–140 nM and high anti-interference ability. The feasibility of the assay was verified by test of malachite green in fish sample. The proposed strategy presents valuable information for the evaluation of the food safety in aquaculture industry.

Carbon dots embedded metal-organic framework@molecularly imprinted nanoparticles for highly sensitive and selective detection of quercetin

A facile and efficient one-pot approach for the synthesis of carbon dots embedded metal-organic framework@molecularly imprinted polymer nanoparticles (CDs@MOF@MIP), which can be used for highly selective and sensitive optosensing of quercetin (QCT), is reported herein for the first time. Metal-organic frameworks (MOFs) with high specific surface area and porosity were first prepared via a room-temperature reaction and used as a matrix to construct MOF-based sensor. Then, highly blue luminescent carbon dots (CDs) were introduced to act as signal transducer that can sense the bonding interactions between the developed sensor and the target molecules and further transduce them to the detectable fluorescence signals. Final, through a surface molecular imprinting process, the resulting CDs@MOF@MIP was obtained. The CDs@MOF@MIP not only exhibited higher selectivity and sensitivity toward target molecular compared to carbon dots embedded metal-organic framework @non-imprinted polymer (CDs@MOF@NIP), but also showed faster reaction rate than CDs-embedded molecularly imprinted polymer (CDs@MIP) derived from the introduction of porous MOF and the optical detection. This proposed sensor was employed to sense trace QCT, and its fluorescence presented a well linear decline with the increasing concentration of QCT from 0 μM to 50.0 μM with a limit of detection of 2.9 nM (S/N = 3), and the precision for eleven replicate detections of 0.5 μM QCT was 1.9%. This developed CDs@MOF@MIP sensor was also used to determine QCT content in real Ginkgo biloba extract capsules with satisfactory performance, and the results were correlated well with those obtained using high performance liquid chromatography.

Selective sensing and visualization of pesticides by ABW-type metal-organic framework based luminescent sensors.

A new ABW-type luminescent metal–organic framework (MOF) namely (H3O)[Zn2L(H2O)]·3NMP·6H2O (1), constructed with eco-friendly Zn2+ and the multicarboxylate intraligand (LH5) was designed, synthesized and fully characterized by X-ray single-crystal diffraction, steady-state absorption and emission spectroscopy, and SEM observations. The MOF-based suspension sensor 1 (NMP) demonstrated high sensitivity to low-concentration pesticides of chlorothalonil (CTL), nitrofen (NF), trifluralin (TFL), and 2,6-dichloro-4-nitroaniline (DCN), which was assigned to the synergistic effect of the photoinduced electron transfer and the fluorescence resonance energy transfer. With the highest luminescent detection efficiency (KSV up to 11.194 μmol−1 and LOD down to 2.93 ppm) to DCN, 1 (NMP) was successfully applied for the selective sensing of DCN. The MOF-based film sensor 1 (film) illustrated the selective visualization sensing of trace amounts of DCN. In addition, based on the high saturated vapor pressure of TFL and the unique bathochromic shift effect to the emission maxima of 1, the MOF-based luminescent vapor sensing device 1 (LED) successfully exhibited operability for sensing of TFL vapor. The results illustrated a feasible approach to construct new MOF-based luminescent sensors for selective sensing and visualization of pesticides.

A dual-responsive luminescent metal-organic framework as a recyclable luminescent probe for the highly effective detection of pyrophosphate and nitrofurantoin.

Pyrophosphate (PPi) is a significant biological anion, and its abnormal level in the human body is regarded as a signal of some diseases. Herein, we developed a method for the detection of PPi using a luminescent ZTMOF-1 via the luminescence turn-on effect. PPi formed hydrogen bonds with the phenyl and pyridine rings in the framework, and ZTMOF-1 could discriminately detect PPi among other phosphorus oxides in both an aqueous solution and a physiological environment. In addition, to the best of our knowledge, this is the first report on the use of a regenerable MOF-based luminescent sensor for the detection of PPi. Moreover, ZTMOF-1 showed an excellent luminescence quenching response to nitrofurantoin (NFT) over other drugs with the detection limit of 0.175 μM. This study presents a dual-responsive regenerable luminescent probe for the detection of PPi and NFT.

Bimetallic MOF-Based Enzyme-Free Sensor for Highly Sensitive and Selective Detection of Dopamine

A bimetallic metal organic frameworks termed as Fe2Ni MIL-88B was fabricated as an enzyme-free dopamine (DA) sensor, which was designed with crystalline porous structure and synthesized by a facile hydrothermal technique. To gain insight into the structure and morphology of Fe2Ni MIL-88B, a series of characterizations such as fourier transform infrared (FTIR), X-ray diffraction (XRD), transmission electron microscopic (TEM) and field emission scanning electron microscopic (FE-SEM) had been performed, proving the as-prepared composite owned hexagonal rod-like structure with the size 633 nm–967 nm in length and 100 nm–167 nm in width. The Fe2Ni MIL-88B modified glass carbon electrode (Fe2Ni MIL-88B/GCE) possessed an excellent electrochemical catalytic performance to DA which are derived from electrochemical test, having been reported to own wider linear range from 1.2 μM–1.8 mM, lower detection limit of 0.40 μM (S/N = 3) and higher sensitivity of 124.7 μA mM−1 cm−2. The proposed sensor exhibited acceptable stability, repeatability and achievability for analyzing real samples. All the evidence suggested a potential application of Fe2Ni MIL-88B in DA detection.

A dual functional MOF-based fluorescent sensor for intracellular phosphate and extracellular 4-nitrobenzaldehyde.

Herein, we present the successful synthesis, characterization and sensing application of a hydrazine functionalized Zr(iv)-based UiO-66 metal-organic framework (MOF) called Zr-UiO-66-N2H3 (1). The guest-free material 1' shows selective and sensitive fluorimetric detection (turn-on mechanism) of phosphate (PO43-) anions in HEPES buffer (10 mM, pH = 7.4) and aqueous medium. It can also fluorimetrically detect (turn-off mechanism) 4-nitrobenzaldehyde (4-NB) in a HEPES : DMSO (9 : 1, v/v) medium with high selectivity and sensitivity. The selectivity for both analytes is retained in the presence of other potentially competitive analytes. The detection limit for PO43- ions is 0.196 μM, which is far below the PO43- level present in the aqueous environment. MOF 1' can detect intracellular phosphate and it also has the capacity to exhibit differences in the intracellular phosphate level. Furthermore, the probe is capable of sensing PO43- ions in real samples such as tap water, lake water, human urine and human blood serum. The sensitivity of the probe for sensing 4-NB is very high (detection limit = 4.7 μM). The possible mechanisms for sensing PO43- ions and 4-NB have been explored in detail by experimental techniques.

Design of a Highly-Stable Pillar-Layer Zinc(II) Porous Framework for Rapid, Reversible, and Multi-Responsive Luminescent Sensor in Water

The hard–soft-acid–base (HSAB) and dual-ligand strategies have been used to construct a pillar-layer luminescent metal–organic framework (MOF) {[Zn2(TRZ)2(DBTDC-O2)]·DMAc}n (1), in which H2DBTDC-O2 = S,S-dioxodibenzothiophen-3,7-dicarboxylic acid and HTRZ = 1,2,4-triazole. Thanks to its high stability in water and quadrangle microporous channels, MOF 1 can be served as a platform of recyclable multi-responsive luminescent sensor for Fe3+, Al3+, SiF62–, Cr2O72–, nitrofurantoin (NFT), and nitrofurazone (NFZ) in water. This is the first MOF-based sensor for detecting SiF62– anion via luminescent enhancement effect. Significantly, 1 also represents a unique example to probe NFZ or NFT by using transition metal MOFs in water, which exhibits the most sensitive sensing ability for NFZ (Ksv = 5.2 × 104 M–1) and NFT (Ksv = 1.8 × 105 M–1) via luminescent quenching.

A turn-on MOF-based luminescent sensor for highly selective detection of glutathione

Glutathione (GSH), as a key regulator for the redox balance of biological processes, was detected with a metal-organic framework (MOF) (UiO-67-sbdc) fluorescence sensor. The fluorescence of UiO-67-sbdc could be effectively enhanced by GSH via an electronic effect between GSH and the ligand of MOF, thus achieving the recognition of GSH. It is the first attempt to design a MOF-based fluorescent sensor to distinguish GSH from cysteine (Cys). This sensor exhibited short response time (<120 s), suitable linear range, and high selectivity towards GSH. Further research conducted in serum also showed a quantitative and selective detection of GSH. Thus, the reported UiO-67-sbdc in this work has its application prospect in clinically judging antioxidant capacity of the body.

Aqueous detection of antibiotics with a Cd(II)-based metal-organic framework constructed by a tetra(1,2,4-triazole)-functionalized-bis(triphenylamine) ligand

A Cd(II)-based MOF (Cd-TTPBA-4) with sra topology is constructed by a tetra(1,2,4-triazole)-functionalized-bis(triphenylamine) ligand (TTPBA-4) showing two types of 1-D channels with partial channel walls built from columnar stacks of non-coordinated triazole-terminated arms. Particularly, it constitutes a rare example of MOF-based luminescent sensor for aqueous selective detection of NZF (nitrofurazone) and NFT (nitrofurantoin) antibiotics.

A Highly Stable Two-Dimensional Copper(II) Organic Framework for Proton Conduction and Ammonia Impedance Sensing.

This work reports the design and fabrication of a proton conductive 2D metal-organic framework (MOF), [Cu(p-IPhHIDC)]n (1) (p-IPhH3 IDC=2-(p-N-imidazol-1-yl)-phenyl-1 H-imidazole-4,5-dicarboxylic acid) as an advanced ammonia impedance sensor at room temperature and 68-98 % relative humidity (RH). MOF 1 shows the optimized proton conductivity value of 1.51×10-3 S cm-1 at 100 °C and 98 % RH. Its temperature-dependent and humidity-dependent proton conduction properties have been explored. The large amount of uncoordinated carboxylate groups between the layers plays a vital role in the resultant conductivity. Distinctly, the fabricated MOF-based sensor displays the required stability toward NH3 , enhanced sensitivity, and notable selectivity for NH3 gas. At room temperature and 68 % RH, it gives a remarkable gas response of 8620 % to 130 ppm NH3 gas and lower detection limit of 2 ppm towards NH3 gas. It is also found that the gas response of the ammonia sensor increases linearly with the increase of NH3 gas concentration under 68-98 % RH and room temperature. Moreover, the sensor indicates excellent reversibility and selectivity toward NH3 versus N2 , H2 , O2 , CO, CO2 , benzene, and MeOH. Based on structural analyses, activation energy calculations, water and NH3 vapor absorptions, and PXRD determinations, proton conduction and NH3 sensing mechanisms are suggested.

A Cuprous/Lanthanide-Organic Framework as the Luminescent Sensor of Hypochlorite.

A new 3D framework {[Eu2 Cu(IN)5 (CO3 )(H2 O)] ⋅3 H2 O}n (1) was obtained and structurally characterized, containing CuI and an unusual lanthanide duplex chain. The luminescent explorations of compound 1 suggest that 1 could emit the characteristic emission of CuI , and 1 can act as the luminescent sensor of ClO- with the detection limit of 10-5 m. Notably, 1 represents the first example of MOF-based sensor for detecting ClO- .

Aqueous phase sensing of bismuth ion using fluorescent metal-organic framework

In this work, the fluorescent CAU-1-(OH)2 was successfully exploited as a fluorescent probe for bismuth ion (Bi3+) in aqueous solutions, which is the first MOF-based fluorescent sensor for Bi3+ up to date. The MOF can exhibit bright green fluorescence in H2O for the intramolecular proton transfer process between the ligand and H2O molecule. In addition, the carboxylate and hydroxyl groups in the MOF can strongly coordinate with Bi3+. Accordingly, CAU-1-(OH)2 can selectively detect Bi3+ in water in 24 s. In addition, the limit of detection of this MOF was calculated to be 2.16 μM, superior to those of some traditional methods such as spectrophotometry and flow injection potentiometry.

Metal-Organic Framework Thin Film Coated Optical Fiber Sensors: A Novel Waveguide-Based Chemical Sensing Platform.

Integration of optical fiber with sensitive thin films offers great potential for the realization of novel chemical sensing platforms. In this study, we present a simple design strategy and high performance of nanoporous metal-organic framework (MOF) based optical gas sensors, which enables detection of a wide range of concentrations of small molecules based upon extremely small differences in refractive indices as a function of analyte adsorption within the MOF framework. Thin and compact MOF films can be uniformly formed and tightly bound on the surface of etched optical fiber through a simple solution method which is critical for manufacturability of MOF-based sensor devices. The resulting sensors show high sensitivity/selectivity to CO2 gas relative to other small gases (H2, N2, O2, and CO) with rapid (<tens of seconds) response time and excellent reversibility, which can be well correlated to the physisorption of gases into a nanoporous MOF. We propose a refractive index based sensing mechanism for the MOF-integrated optical fiber platform which results in an amplification of inherent optical absorption present within the MOF-based sensing layer with increasing values of effective refractive index associated with adsorption of gases.