Ultrasensitive detection of zearalenone based on electrochemiluminescent immunoassay with Zr-MOF nanoplates and Au@MoS2 nanoflowers

In this work, an effective competitive-type electrochemiluminescence (ECL) immunosensor was constructed for zearalenone determination by using Zr-MOF nanoplates as the ECL luminophore and Au@MoS2 nanoflowers as the substrate material. Zr-MOF have an ultra-thin sheet-like structure that accelerates the transfer of electrons, ions and co-reactant intermediates, which exhibited strong and stable anodic luminescence. The three-dimensional Au@MoS2 nanoflowers would form a thin film modification layer on the glassy carbon electrode (GCE). And its good electrical conductivity and higher specific surface area utilization further improving the sensitivity of the ECL immunosensor. Under the optimized conditions, the proposed immunosensor exhibited satisfactory stability, sensitivity and accuracy, and its ECL signal was proportional to the logarithm of ZEN concentration (0.0001-100 ng/mL) and the limit of detection (LOD) was 0.034 pg/mL. In addition, the results of recovery experiment acquired for wheat flour and pig urine samples further proved the feasibility of the immunosensor for the detection of real samples, indicating its potential for ultrasensitive detection of ZEN.

Triplet Generation Through Singlet Fission in Metal-Organic Framework: An Alternative Route to Inefficient Singlet-Triplet Intersystem Crossing

High quantum yield triplets, populated by initially prepared excited singlets, are desired for various energy conversion schemes in solid working compositions like porous MOFs. However, a large disparity in the distribution of the excitonic center of mass, singlet-triplet intersystem crossing (ISC) in such assemblies is inhibited, so much so that a carboxy-coordinated zirconium heavy metal ion cannot effectively facilitate the ISC through spin-orbit coupling. Circumventing this sluggish ISC, singlet fission (SF) is explored as a viable route to generating triplets in solution-stable MOFs. Efficient SF is achieved through a high degree of interchromophoric coupling that facilitates electron super-exchange to generate triplet pairs. Here we show that a predesigned chromophoric linker with extremely poor ISC efficiency (kISC ) butE S 1 ≥ 2 E T 1 ${{E}_{{S}_{1}}\ge {2E}_{{T}_{1}}}$ form triplets in MOF in contrast to the frameworks that are built from linkers with sizable kISC butE S 1 ≤ 2 E T 1 ${{E}_{{S}_{1}}\le {2E}_{{T}_{1}}}$ . This work opens a new photophysical and photochemical avenue in MOF chemistry and utility in energy conversion schemes.

Performance of Zr-Based Metal-Organic Framework Materials as In Vitro Systems for the Oral Delivery of Captopril and Ibuprofen

Zr-based metal-organic framework materials (Zr-MOFs) with increased specific surface area and pore volume were obtained using chemical (two materials, Zr-MOF1 and Zr-MOF3) and solvothermal (Zr-MOF2) synthesis methods and investigated via FT-IR spectroscopy, TGA, SANS, PXRD, and SEM methods. The difference between Zr-MOF1 and Zr-MOF3 lies in the addition of reactants during synthesis. Nitrogen porosimetry data indicated the presence of pores with average dimensions of ~4 nm; using SANS, the average size of the Zr-MOF nanocrystals was suggested to be approximately 30 nm. The patterns obtained through PXRD were characterized by similar features that point to well-crystallized phases specific for the UIO-66 type materials; SEM also revealed that the materials were composed of small and agglomerate crystals. Thermogravimetric analysis revealed that both materials had approximately two linker deficiencies per Zr6 formula unit. Captopril and ibuprofen loading and release experiments in different buffered solutions were performed using the obtained Zr-based metal-organic frameworks as drug carriers envisaged for controlled drug release. The carriers demonstrated enhanced drug-loading capacity and showed relatively good results in drug delivery. The cumulative percentage of drug release in phosphate-buffered solution at pH 7.4 was higher than that in buffered solution at pH 1.2. The release rate could be controlled by changing the pH of the releasing solution. Different captopril release behaviors were observed when the experiments were performed using a permeable dialysis membrane.

Process intensification of synthesis of metal organic framework particles assisted by ultrasound irradiation

This study synthesized UiO-66, a typical Zr-Metal Organic Framework (MOF), by using an ultrasound-assisted synthesis method to reduce the synthesis time. This method was short-time ultrasound irradiation at the initial stage of the reaction. As compared with average particle size of conventional solvothermal method (=192 nm), averaged particle size by the ultrasound-assisted synthesis method showed particle sizes that were smaller on average, ranging from 56 to 155 nm. In order to compare the relative reaction rates of the solvothermal method and the ultrasound-assisted synthesis method, the cloudiness of the reaction solution in the reactor was observed with a video camera, and the luminance was calculated from the images obtained by the video camera. It was found that the ultrasound-assisted synthesis method showed a faster increase in luminance and shorter induction time than the solvothermal method. The slope of the luminance increase during the transient period was also found to become increase with the addition of ultrasound, which also affects the growth of particles. Observation of the aliquoted reaction solution confirmed that particle growth was faster in the ultrasound-assisted synthesis method than in the solvothermal method. Numerical simulations were also performed using MATLAB ver. 5.5 to analyze the unique reaction field generated by ultrasound. Bubble radius and temperature inside a cavitation bubble was obtained using the Keller-Miksis equation, which reproduces the motion of a single bubble. The bubble radius expanded and contracted repeatedly according to the ultrasound sound pressure, and eventually collapsed. The temperature at the time of collapse was extremely high, exceeding 17,000 K. It was confirmed that the high-temperature reaction field generated by ultrasound irradiation promoted nucleation, leading to a reduction in particle size and induction time.

Ru(II)-modified metal organic framework as excellent electrochemiluminescence emitter for ultrasensitive nicotine detection

The sensitive and selective nicotine detection in cigarette is necessary due to the cigarette addiction problem and the neurotoxicity of nicotine on human body. In this study, a novel electrochemiluminescence (ECL) emitter with excellent performance was prepared for nicotine analysis, by combining Zr-based metal organic framework (Zr-MOF) and branched polyethylenimine (BPEI)-coated Ru(dcbpy)₃²⁺ through electrostatic interaction. Ru(dcbpy)₃²⁺ integrated by Zr-MOF could be catalyzed by the reaction intermediates SO₄^•-, produced from the co-reactant S₂O₈^2-, resulting in a significant increase in ECL response. Interestingly, SO₄^•- with strong oxidizing ability could preferentially oxidize nicotine, leading to ECL quenching. The constructed ECL sensor based on the Ru-BPEI@Zr-MOF/S₂O₈^2- system displayed ultrasensitive determination of nicotine with a lower detection limit of 1.9 × 10^-12 M (S/N = 3), which is three orders lower than previously reported ECL results and 4-5 orders lower than that of other types of method. This method puts forward a new approach for building efficient ECL system with greatly improved ECL sensitivity for nicotine detection.

Multifunctional Zr-MOF Based on Bisimidazole Tetracarboxylic Acid for pH Sensing and Photoreduction of Cr(VI)

Herein, a new luminescent zirconium MOF [Zr-BBI, BBI = 4,4',4″,4‴-(1,4-phenylenebis(1H-imidazole-2,4,5-triyl))tetrabenzoic acid] was successfully constructed by a rationally designed functionalized bisimidazole tetracarboxylic acid ligand. Zr-BBI consists of eight-connected Zr₆ clusters and four-connected BBI ligands. The high connection mode must be responsible for the high stabilities of Zr-BBI in both acidic and basic systems. Apart from the high stability, the inherent bisimidazole units endow Zr-BBI with the traits of intense fluorescent emission as well as the protonation/deprotonation behavior. Therefore, Zr-BBI could display a highly sensitive fluorescence response along with the varying pH values in the aqueous solutions and act as a pH sensing scaffold, especially in the pH value range from 4.6 to 7.12. Zr-BBI also shows good fluorescence detection performance toward Cr₂O₇^2- at a low concentration with a high K_SV value up to 6.49 × 10⁴ M^-1. Moreover, by the utilization of Zr-BBI as a catalyst, Cr(VI) could be effectively photoreduced to Cr(III) in aqueous solution under visible light irradiation, in which the introduction of a hole scavenger (benzyl alcohol) could further significantly enhance the photocatalytic efficiency. Compared to that of the recently representative MOFs, the k value of the photocatalytic reaction over Zr-BBI is as high as 0.073 min^-1. With the consideration of the presented results, Zr-BBI can serve as a multifunctional platform for efficiently sensing and photoreducing Cr₂O₇^2- in an aqueous system, which fully illustrates the feasibility that introducing specific functional groups in the framework of MOFs would enhance the related photocatalytic activity.

Enhancing toxic gas uptake performance of Zr-based MOF through uncoordinated carboxylate and copper insertion; ammonia adsorption

This study reports the development of a new type of Zr-based MOF by inserting copper and carboxylate into HCl modulated UiO-67 (UiO-67-vac) which gained higher surface area/vacant than UiO-67. Copper was inserted into MOF containing uncoordinated carboxylate group, to create open metal site in the form of -COOCu which called UiO-67-ox-Cu. PXRD, FTIR, BET, SEM, EDS, UV-Vis and XPS were used to characterize the obtained MOFs. As expected, UiO-67-ox-Cu exhibits the highest ammonia capacity (178.3 mg/g) among UiO-67 (104 mg/g) and UiO-67-vac (121 mg/g) at 298 K and 1 bar pressure. In fact, the significant increase in ammonia uptake of UiO-67-ox-Cu is related to the modified binding affinity of -COOCu groups with ammonia. Moreover, UiO-67-vac with the highest surface area showed the hydrogen adsorption capacity of 18.75 mg/g at 77 K, which is comparable or even superior to the previously reported value. Interestingly, adsorption capacities were retained with slight changes around five cycles and three regeneration temperatures, 25, 60 and 120 °C under vacuum pressure which were proved by PXRD after ammonia adsorption/desorption. The good results obtained in the current work clearly show the role of postsynthesis functionalization approach for creation of new metal/active sites into MOFs.

Synergistic Effect between Zr-MOF and Phosphomolybdic Acid with the Promotion of TiF4 Template

Metal-Organic Framework (MOF) materials are often modified or functionalized, and then the crystal size and morphology of MOF materials are changed. In the process of preparing UiO-66 confined phosphomolybdic acid (PMA) composites (PU), the TiF₄-modified PU (PMA + UiO-66) composite catalyst (TiF₄-PU) was successfully synthesized by adding titanium tetrafluoride, and the catalytic desulfurization activity was excellent. Similarly, the reaction mechanism was investigated by means of infrared spectroscopy, Raman spectroscopy, XPS, and UV/Vis spectroscopy. The results show that the addition of TiF₄ not only changes the appearance and color of the catalyst, but also changes the valence distribution of the elements in the catalyst. The number of oxygen vacancies in the MOF increases due to the addition of TiF₄, and more electrons are transferred from the Zr-MOF to PMA to form more Mo⁵⁺, which improved the performance of oxidative desulfurization in comparison. Thus, a stronger strong metal-support interaction (SMSI) effect is observed for TiF₄-modified PU catalysts. In addition, the quenching experiment of free radicals shows that ·OH radical is the main active substance in the oxidative desulfurization reaction over TiF₄-PU catalyst.

Colorimetric Sensor Array for Human Semen Identification Designed by Coupling Zirconium Metal-Organic Frameworks with DNA-Modified Gold Nanoparticles

Rapid and accurate identification of semen is critical for male infertility diagnosis and the arrangement of personalized treatment. However, the complexity and diversity of samples impose lots of restrictions in detection. To solve this problem, we propose a colorimetric sensor array in this work by coupling zirconium metal-organic frameworks (Zr-MOFs) with single-stranded-DNA-decorated gold nanoparticles (ssDNA-AuNPs) for human semen identification. Because of the coordination interactions between the Zr₆ clusters and the DNA phosphate backbone, as well as π-π stacking and H-bonding, Zr-MOFs can absorb and precipitate AuNPs with the aid of single-stranded DNA. What's more, addition of semen samples in the test solution, proteins, or other contents in the samples will affect the co-precipitation of Zr-MOFs and ssDNA-AuNPs. Subsequently, the color of the supernatant will change and a method to identify human semen can be developed. Further studies reveal that the method can completely detect different semen cases based on the differences in inclusions, demonstrating the characteristics of simplicity, feasibility, and sensitivity in the application of male infertility diagnosis.

Electrochemical determination of Salmonella typhimurium by using aptamer-loaded gold nanoparticles and a composite prepared from a metal-organic framework (type UiO-67) and graphene

An aptamer based assay is described for the determination of Salmonella typhimurium (S.typhimurium). A metal-organic framework-graphene composite of type UiO-67/GR is used as the substrate, and an aptamer-gold nanoparticles-horseradish peroxidase (Apt-AuNP-HRP) conjugate the signal amplification probe. A phosphate-terminal and partially complementary DNA (cDNA) of the aptamer is covalently bound to UiO-67/GR via the chemical complexation between phosphate and Zr-OH groups of UiO-67, and then S. typhimurium and cDNA will compete for the binding sites. The binding of Apt-AuNP-HRP to S.typhimurium leads to the formation of strong conjugates. The unbound signal probes then attach to the surface of a glassy carbon electrode via hybridization with cDNA. This generates a large current response (best measured at a potential as low as -0.02 V vs. saturated calomel electrode) under the catalytic action of HRP on the H₂O₂-hydroquinone system. Under the optimal conditions, the differential pulse voltammetric signal decreases linearly in the 2 × 10¹ - 2 × 10⁸ cfu·mL^-1 S.typhimurium concentration range, with a lower detection limit of 5 cfu·mL^-1 (based on S/N = 3). The method was successfully applied to the detection of S. typhimurium in spiked milk samples. Graphical abstract Schematic presentation of electrochemical determination of Salmonella typhimurium (S.typhimurium). A metal-organic framework (type UiO-67) and graphene (GR) composite were used as substrate, and gold nanoparticles carrying horseradish peroxidase (HRP) for signal amplification. HQ: hydroquinone; cDNA: complementary DNA of aptamer.

Organophosphate hydrolase conjugated UiO-66-NH2 MOF based highly sensitive optical detection of methyl parathion

The hexahistidine-tagged organophosphorus hydrolase (OPH^6His) has been immobilized on a Zr-MOF, namely UiO-66-NH₂. The resulting enzyme-MOF composite was used as a carrier to facilitate the hydrolysis of an organophosphate pesticide, i.e., methyl parathion in to p-nitrophenol (PNP). The formation of PNP took place in direct proportion to the added pesticide concentration. Coumarin1 (7-diethylamino-4-methylcoumarin) was then introduced in the reaction mixture as a reporter fluorescent molecule. As PNP acted to quench the fluorescence of coumarin1, it became possible to detect methyl parathion over a wide concentration range of 10-10⁶ ng/mL with an achievable limit of quantification as 10 ng/mL. The immobilization of OPH^6His on the surface of UiO-66-NH₂ was found to endow an improvement in the enzymatic activity by about 37%. The OPH^6His/UiO-66-NH₂ conjugate was reusable for at least up to eight times and also found stable toward long-term storage (minimum 60 days). The potential practical utility of the above proposed sensing method has been demonstrated by employing it for an accurate analysis of pesticide-spiked food samples.

Ligands-Coordinated Zr-Based MOF for Wastewater Treatment

Isostructural zirconium-based metal⁻organic frameworks (Zr-MOFs) have attracted the attention of researchers because of their remarkable stability at high temperatures and high pressures and their chemical stabilities against acids and bases. Due to this stability, Zr-MOFs can be utilized in adsorption research, and the adsorption performance of a Zr-MOF depends on the pore size and the surroundings of the MOF. In this study, as the dimensions changed and the adsorption was carried out, the Zr-MOF material remained stable, and the adsorption of the best state was achieved at 235 mg/g. Through the simulation of theoretical kinetic models of Zr-MOFs, we initially postulated that the adsorption capacity is proportional to the pore size and that acid orange 7 (AO7) was adsorbed by the MOFs. Afterwards, we verified our hypotheses through a series of Brunauer⁻Emmett⁻Teller (BET) data analysis; non-local density function theory (NLDFT) was mainly used to analyze the data. Moreover, we determined that physical adsorption occurs on the surface of the MOFs during the adsorption process, while chemisorption occurs in the form of dye molecules combining with active sites. Ultimately, we concluded that the larger the pore size, the stronger the adsorption capacity, and this contribution casts a new light on the issue of wastewater treatment.