Ferric Oxide Nanocrystals-Embedded Co/Fe-MOF with Self-Tuned d-Band Centers for Boosting Urea-Assisted Overall Water Splitting.

A novel semiconductive Co/Fe-MOF embedded with Fe2 O3 nanocrystals (Fe2 O3 @CoFe-MOF) is developed as a trifunctional electrocatalyst for the urea oxidation reaction (UOR), oxygen evolution reaction (OER), and hydrogen evolution reaction for enhancing the efficiency of the hydrogen production via the urea-assisted overall water splitting. Fe2 O3 @CoFe-TPyP-MOF comprises unsaturated metal-nitrogen coordination sites, affording enriched defects, self-tuned d-band centers, and efficient π-π interaction between different layers. Density functional theory calculation confirms that the adsorption of urea can be optimized at Fe2 O3 @CoFe-TPyP-MOF, realizing the efficient adsorption of intermediates and desorption of the final product of CO2 and N2 characterized by the in situ Fourier transform infrared spectroscopy. The two-electrode urea-assisted water splitting device-assembled with Fe2 O3 @CoFe-TPyP-MOF illustrates a low cell voltage of 1.41 V versus the reversible hydrogen electrode at the current density of 10 mA cm-2 , attaining the hydrogen production rate of 13.13 µmol min-1 in 1 m KOH with 0.33 m urea. The in situ electrochemical Raman spectra and other basic characterizations of the used electrocatalyst uncover that Fe2 O3 @CoFe-TPyP-MOF undergoes the reversible structural reconstruction after the UOR test, while it demonstrates the irreversible reconstruction after the OER measurement. This work redounds the progress of urea-assisted water spitting for hydrogen production.

Single-Atom Co─O4 Sites Embedded in a Defective-Rich Porous Carbon Layer for Efficient H2O2 Electrosynthesis.

The production of hydrogen peroxide (H2O2) via the two-electron electrochemical oxygen reduction reaction (2e- ORR) is an essential alteration in the current anthraquinone-based method. Herein, a single-atom Co─O4 electrocatalyst is embedded in a defective and porous graphene-like carbon layer (Co─O4@PC). The Co─O4@PC electrocatalyst shows promising potential in H2O2 electrosynthesis via 2e- ORR, providing a high H2O2 selectivity of 98.8% at 0.6 V and a low onset potential of 0.73 V for generating H2O2. In situ surface-sensitive attenuated total reflection Fourier transform infrared spectra and density functional theory calculations reveal that the electronic and geometric modification of Co─O4 induced by defective carbon sites result in decreased d-band center of Co atoms, providing the optimum adsorption energies of OOH* intermediate. The H-cell and flow cell assembled using Co─O4@PC as the cathode present long-term stability and high efficiency for H2O2 production. Particularly, a high H2O2 production rate of 0.25 mol g-1 cat h-1 at 0.6 V can be obtained by the flow cell. The in situ-generated H2O2 can promote the degradation of rhodamine B and sterilize Staphylococcus aureus via the Fenton process. This work can pave the way for the efficient production of H2O2 by using Co─O4 single atom electrocatalyst and unveil the electrocatalytic mechanism.

A Robust n-n Heterojunction: CuN and BN Boosting for Ambient Electrocatalytic Nitrogen Reduction to Ammonia.

An n-n type heterojunction comprising with CuN and BN dual active sites is synthesized via in situ growth of a conductive metal-organic framework (MOF) [Cu3 (HITP)2 ] (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) on hexagonal boron nitride (h-BN) nanosheets (hereafter denoted as Cu3 (HITP)2 @h-BN) for the electrocatalytic nitrogen reduction reaction (eNRR). The optimized Cu3 (HITP)2 @h-BN shows the outstanding eNRR performance with the NH3 production of 146.2 µg h-1 mgcat -1 and the Faraday efficiency of 42.5% due to high porosity, abundant oxygen vacancies, and CuN/BN dual active sites. The construction of the n-n heterojunction efficiently modulates the state density of active metal sites toward the Fermi level, facilitating the charge transfer at the interface between the catalyst and reactant intermediates. Additionally, the pathway of NH3 production catalyzed by the Cu3 (HITP)2 @h-BN heterojunction is illustrated by in situ FT-IR spectroscopy and density functional theory calculation. This work presents an alternative approach to design advanced electrocatalysts based on conductive MOFs.

Sensitive detection of Escherichia coli in diverse foodstuffs by electrochemical aptasensor based on 2D porphyrin-based COF.

The two-dimensional porphyrin-based covalent organic framework (denoted by Tph-TDC-COF) was used as the sensitive layerto build an aptamer-based electrochemical sensor for the detection of Escherichia coli (E.coli). Tph-TDC-COF produced with 5,10,15,20-tetrakis(4-aminophenyl)-21H, 23H-porphine (Tph) and [2,2'-bithiophene]-2,5'-dicarbaldehyde (TDC) as building blocks exhibited a highly conjugated structure, outstanding conductivity, large specific surface area, and strong bioaffinity towards aptamers. The adoption of Tph-TDC-COF-modified electrode resulted in improved sensing performance and increased anchoring affinity toward the E.coli-targeted aptamer. Under optimal conditions, the Tph-TDC-COF-based electrochemical aptasensor demonstrated an extremely low detection limit of 0.17 CFU mL-1 for E.coli detection within a linear range of 10 to 1 × 108 CFU mL-1, accompanied by good stability, excellent reproducibility and regeneration ability, and wide practical applications. The current electrochemical aptasensing technique has the potential to be extended to detect different foodborne bacteria using specific aptamer, therefore widening the application of COFs in biosensing and food safety fields.

Impedimetric aptasensor based on porphyrin-based covalent-organic framework for determination of diethylstilbestrol.

An impedimetric sensing strategy was developed for sensitively determining diethylstilbestrol (DES) based on a platform of porphyrin-containing covalent-organic framework (p-COF). The p-COF was synthesized using 5,10,15,20-tetra (4-aminophenyl) porphyrin (TAPP) and 1,3,6,8-tetrakis(4-formylphenyl) pyrene (TFPy) as building blocks via condensation reaction, for which p-COF was named as TAPP-TFPy-COF. Considering the large specific surface area (302.9 m2 g-1), high porosity, rich nitrogen functionality, superior electrochemical activity, and strong bioaffinity toward DNA strands, the TAPP-TFPy-COF-based platform exhibited enhanced, non-label, and amplified electrochemical signal, large number of immobilized DES-targeted aptamer strands, and fast-response toward the analyte. Electrochemical results reveal that the TAPP-TFPy-COF-based aptasensor promoted the sensing performance for the detection of DES, resulting in an extremely low limit of detection of 0.42 fg mL-1 within a DES concentration ranging from 1 fg mL-1 to 0.1 pg mL-1, which was substantially lower than those of most reported DES sensors. Furthermore, the TAPP-TFPy-COF-based aptasensor possessed outperformed stability, high selectivity, ascendant reproducibility, and acceptable applicability in diverse environments. The recovery values for DES detection in milk, tap water, and frozen shrimp were in the range 91.80-118.50% with low relative standard deviation of 0.11-4.26%. This work provides a new sensing electrochemical approach based on COF network for DES detection and shows a deep insight into the construction of COF-based biosensors, which can be extended to be used for other target compounds.

Impedimetric aptasensor based on zirconium-cobalt metal-organic framework for detection of carcinoembryonic antigen.

A zirconium-cobalt metal-organic framework (ZrCo-MOF) was prepared and used as sensing material to fabricate an aptasensor for trace detection of carcinoembryonic antigen (CEA). The ZrCo-MOF integrates the 3D porous structure and abundant defects of the MOF framework, the catalytic activity and inherent redox behavior of Co, and high stability of Zr-MOF, providing abundant active sites to effectively anchor aptamers. As a result, the ZrCo-MOF-based aptasensor shows high sensitivity to detect CEA via specific recognition between aptamer and CEA, as well as the formation of aptamer-CEA complex. A detection limit of 0.35 fg·mL-1 was deduced from the electrochemical impedance spectroscopy within a wide linear range of 0.001-100 pg·mL-1 for CEA, which was substantially lower than those of most reported CEA biosensors. The ZrCo-MOF-based aptasensor also shows good selectivity, reproducibility, regenerability, stability, and applicability for human serum sample. Therefore, the developed ZrCo-MOF-based aptasensor will be promising for ultrasensitive detection of biomarkers and the early diagnosis of cancer. This work presents a novel electrochemical aptasensor for the trace detection of carcinoembryonic antigen (CEA) based on a zirconium-cobalt metal-organic framework (ZrCo-MOF), which shows low detection limit of 0.35 fg·mL-1, high selectivity as well as good reproducibility, regenerability, stability, and applicability. The result provides a promising approach to detect the cancer biomarkers in an early age.

MOF@COF Heterostructure Hybrid for Dual-Mode Photoelectrochemical-Electrochemical HIV-1 DNA Sensing.

We developed a novel metal-organic framework (MOF)@covalent-organic framework (COF) hybrid with a hierarchical nanostructure and excellent photoactivity, which further acted as the bifunctional platform of a dual-mode photoelectrochemical (PEC) and electrochemical (EC) biosensor for detecting HIV-1 DNA via immobilizing the HIV-1 DNA probe. First, the presynthesized Cu-MOF nanoellipsoids were used as the template for the in situ growth of the COF network, which was synthesized using copper-phthalocyanine tetra-amine (CoPc-TA) and 2,9-bis[p-(formyl)phenyl]-1,10-phenanthroline as building blocks through the Schiff base condensation. In view of the large specific surface area, abundant reserved amino group, excellent electrochemical activity, and high photoactivity, the obtained Cu-MOF@CuPc-TA-COF heterostructure not only can serve as the sensitive platform for anchoring the HIV-1 DNA probe strands but also can be utilized as the signal transducers for PEC and EC biosensors. Thereby, the constructed biosensor shows the sensitive and selective analysis ability toward the HIV-1 target DNA via the complementary hybridization between probe and target DNA strands. The dual-mode PEC and EC measurements revealed that the Cu-MOF@CuPc-TA-COF-based biosensor displayed a wide linear detection range from 1 fM to 1 nM and an extremely low limit of detection (LOD) of 0.07 and 0.18 fM, respectively. In addition, the dual-mode PEC-EC biosensor also demonstrated remarkable selectivity, high stability, good reproducibility, and preferable regeneration ability, as well as acceptable applicability, for which the detected HIV-1 DNA in human serum showed good consistency with real concentrations. Thereby, the present work can open a new dual-mode PEC-EC platform for detecting HIV-1 DNA based on the porous-organic framework heterostructure.

Surface plasmon resonance aptasensor based on niobium carbide MXene quantum dots for nucleocapsid of SARS-CoV-2 detection.

A novel label-free surface plasmon resonance (SPR) aptasensor has been constructed for the detection of N-gene of SARS-CoV-2 by using thiol-modified niobium carbide MXene quantum dots (Nb2C-SH QDs) as the bioplatform for anchoring N-gene-targeted aptamer. In the presence of SARS-CoV-2 N-gene, the immobilized aptamer strands changed their conformation to specifically bind with N-gene. It thus increased the contact area or enlarged the distance between aptamer and the SPR chip, resulting in a change of the SPR signal irradiated by the laser (He-Ne) with the wavelength (λ) of 633 nm. Nb2C QDs were derived from Nb2C MXene nanosheets via a solvothermal method, followed by functionalization with octadecanethiol through a self-assembling method. Subsequently, the gold chip for SPR measurements was modified with Nb2C-SH QDs via covalent binding of the Au-S bond also by self-assembling interaction. Nb2C-SH QDs not only resulted in high bioaffinity toward aptamer but also enhanced the SPR response. Thus, the Nb2C-SH QD-based SPR aptasensor had low limit of detection (LOD) of 4.9 pg mL-1 toward N-gene within the concentration range 0.05 to 100 ng mL-1. The sensor also showed excellent selectivity in the presence of various respiratory viruses and proteins in human serum and high stability. Moreover, the Nb2C-SH QD-based SPR aptasensor displayed a vast practical application for the qualitative analysis of N-gene from different samples, including seawater, seafood, and human serum. Thus, this work can provide a deep insight into the construction of the aptasensor for detecting SARS-CoV-2 in complex environments. A novel label-free surface plasmon resonance aptasensor has been constructed to detect sensitively and selectively the N-gene of SARS-CoV-2 by using thiol-modified niobium carbide MXene quantum dots as the scaffold to anchor the N-gene-targeted aptamer.

Conjugated bimetallic cobalt/iron polyphthalocyanine as an electrochemical aptasensing platform for impedimetric determination of enrofloxacin in diverse environments.

The synthesis of bimetallic cobalt/iron polyphthalocyanine (represented by polyCoFePc) network via a modified solid-phase synthesis method is described. It was exploited as a platform for anchoring enrofloxacin (ENR)-targeted aptamer strands, thus, fabricating a label-free impedimetric aptasensor for determination of ENR. The polyCoFePc exhibited a porous two-dimensional (2D) conjugated nanostructure and rich functional groups, and showed a superior binding interaction toward aptamer strands as compared to monometallic polyFePc and polyCoPc networks. This finding was attributed to structural defects and increased active binding sites, thereby giving a highly sensitive detection ability toward ENR. By using electrochemical impedance spectroscopy (EIS), the polyCoFePc-based electrochemical aptasensor exhibited an extremely low detection limit of 0.06 fg mL-1 within the ENR concentration from 0.1 fg mL-1 to 100 pg mL-1, along with high selectivity, good reproducibility, and remarkable stability. Interestingly, the constructed polyCoFePc-based aptasensor also demonstrated wide practicability in various environments. The recoveries of ENR spiked into river water, milk, and pork samples ranged within 91.2 - 107.2%, 90.5 - 109.6%, and 91.2 - 102.3%, respectively.

Electrospun zirconium oxide embedded in graphene-like nanofiber for aptamer-based impedimetric bioassay toward osteopontin determination.

An impedimetric bioassay was constructed based on a nanohybrid of zirconium oxide nanoparticles and graphene-like nanofiber (denoted by ZrO2@GNF) for the determination of osteopontin (OPN). A series of ZrO2@GNF nanohybrids with different morphologies and nanostructures were derived from zirconium-based metal-organic frameworks (UiO-66) entrapped within the electric spun polyacrylonitrile (PAN) fiber (represented by UiO-66@PAN) by calcination at different temperatures. The basic characterizations revealed that the UiO-66@PAN nanofibers were collapsed into short nanorods. As such, homogeneously distributed ZrO2 nanoparticles were found to be embedded within the GNF nanostructure. This transition in the chemical structure and nanostructure not only can greatly enhance the electrochemical conductivity of the nanohybrid but also can strengthen the adsorbed bioaffinity toward OPN aptamer strands. As compared with bioassays based on ZrO2@GNF calcined at 500 °C and 900 °C, the ZrO2@GNF nanohybrid obtained at 700 °C (ZrO2@GNF700) demonstrated superior sensing performance, showing a determination limit of 4.76 fg mL-1 within a OPN concentration ranging 0.01 pg mL-1 to 2.0 ng mL-1. It also displayed high selectivity, accompanied by  good reproducibility and stability, acceptable applicability, and excellent repeatability. Graphical abstractSchematic representation of an impedimetric aptasensor based on nanohybrids of zirconium oxide nanoparticles and graphene-like nanofiber (ZrO2@CNF) was constructed for osteopontin detection. The ZrO2@CNF700 nanohybrid-based aptasensor demonstrated superior sensing performances, providing a promising tool for detecting cancer markers in biomedical diagnosis.

Nonenzymatic amperometric sensor for hydrogen peroxide released from living cancer cells based on hierarchical NiCo2O4-CoNiO2 hybrids embedded in partially reduced graphene oxide.

The synthesis of hierarchical NiCo2O4-CoNiO2 hybrids embedded in partially reduced graphene oxide (represented by NiCo2O4/CoNiO2@pPRGO) is described. They were derived from ultrathin CoNi-based zeolitic imidazolate framework (CoNi-ZIF) nanosheets vertically grew on three-dimensional (3D) pRGO networks by pyrolysis at different temperatures (300, 600, and 900 °C) in N2 atmosphere. Transmission electron microscopy, X-ray diffraction, and X-ray photoemission spectroscopy measurements showed that the metal coordination centers (Co or Ni) were transferred into NiCo2O4 spinel and CoNiO2 nanostructures, along with a small number of metallic states of Co and Ni. In view of good electrochemical conductivity and large specific surface area of pRGO, good catalytic activity of Co- and Ni-contained NPs, and homogeneous distribution of NPs within the pRGO network, the NiCo2O4/CoNiO2@pRGO600 nanohybrid calcined at 600 °C displayed superior electrocatalytic activity toward hydrogen peroxide (H2O2) reduction. A glassy carbon electrode modified with NiCo2O4/CoNiO2@pRGO600 was used for determination of H2O2 by amperometry at an applied potential of - 0.4 V vs. Ag/AgCl. The nonenzymatic amperometric sensor exhibited high sensitivity and low detection limit (0.41 µM) within a wide working range (5 µM-3 mM and 3-12 mM) toward H2O2, as well as good selectivity, reproducibility, and long-term stability. Benefiting from the good biocompatibility and remarkable analytical performances of NiCo2O4/CoNiO2@pRGO600, the assay was used to determine real-time H2O2 released from living cancer cells. Graphical abstract.

A bimetallic (Cu-Co) Prussian Blue analogue loaded with gold nanoparticles for impedimetric aptasensing of ochratoxin a.

Bimetallic (Cu-Co) Prussian Blue analogs (PBAs) were coupled to gold nanoparticles to give a nanocomposite of type AuNP@CuCoPBA. It is shown to be a viable material for the impedimetric aptamer-based determination of ochratoxin A (OTA). Basic characterizations revealed that the chemical composition and crystal structure of AuNP@CuCoPBA is similar to that of pristine CuCo PBA. Nevertheless, the nanocube shape of CoCu PBA is converted to small nanoparticles on addition of AuNPs. Compared with CuCoPBA-based aptasensor, the AuNP@CuCoPBA-based assay exhibits excellent electrochemical conductivity, strong aptamer binding interaction, and high G-quadruplex stability. Electrochemical impedance spectroscopy revealed that the assay has limits of detection as low as 5.2 fg mL-1 of OTA, a response in the 50 fg mL-1 to 10 ng mL-1 concentration range, high selectivity, good reproducibility, repeatability, and acceptable applicability. In our perception, it represents a universal and powerful method for aptamer strand immobilization. It may be applied to the determination of various other analytes for which aptamers are available. Graphical abstract Schematic presentation of the preparation of a novel bimetallic Cu-Co PBAs coupling with gold nanoparticles (AuNPs) was supplied. The AuNP@CuCoPBA composite was applied for the sensitive detection of ochratoxin A (OTA). The impedimetric aptasensensor based on AuNP@CuCoPBA displays extremely low limits of detection toward OTA (5.2 fg mL-1), along with high selectivity, good reproducibility, high stability, repeatability, and acceptable applicability.

Gold nanoparticles conjugated to bimetallic manganese(II) and iron(II) Prussian Blue analogues for aptamer-based impedimetric determination of the human epidermal growth factor receptor-2 and living MCF-7 cells.

An aptamer-based assay is described for the determination of trace levels of the cancer marker human epidermal growth factor receptor-2 (HER2) and living MCF-7 cells. The method is based on the use of a bimetallic MnFe Prussian blue analogue coupled to gold nanoparticles (MnFePBA@AuNP). Compared to pristine MnFe PBA nanocubes, the series of MnFePBA@AuNP exhibits a core-shell spherical nanostructure, and the shell thickness decreases from 99.9 nm down to 49.3 nm on increasing the fraction of AuNPs. The composite was placed on a gold electrode and incubated with the aptamer solution through electrostatic interaction. Then the modified electrode was employed to detect HER2 and MCF-7 cells using [Fe(CN)6]3-/4- as redox probe and displays good responses to both of them. Electrochemical impedance spectroscopy data show that the signal variation between each step during the whole procedure for the HER2 and MCF-7 cells detection can be embodied as the resistance value change between the [Fe(CN)6]3-/4- and electrode surface. The assay has a very low detection limit (0.247 pg∙mL-1) and works in the 0.001-1.0 ng∙mL-1 HER2 concentration range. It was also used to sense HER2 in MCF-7 cells, and this results in an assay that works within the 500-5 × 104 cell∙mL-1 cell concentration range and a 36 cell∙mL-1 detection limit. Furthermore, the aptamer-based assay is selective, acceptably reproducible, stable, and well feasible for the detection of HER2 and living MCF-7 cells in human serum. Graphical abstract Schematic of an electrochemical aptasensor based on the bimetallic MnFe Prussian blue analogue (MnFe PBA) coupling with gold nanoparticles (represented by MnFePBA@AuNPs). It was employed as the aptasensor for human epidermal growth factor receptor-2 (HER2), and living MCF-7 cells.

Core-Shell Heterostructured CuFe@FeFe Prussian Blue Analogue Coupling with Silver Nanoclusters via a One-Step Bioinspired Approach: Efficiently Nonlabeled Aptasensor for Detection of Bleomycin in Various Aqueous Environments.

We synthesized novel core-shell heterostructured Prussian blue analogue (PBA) nanospheres coupled with silver nanoclusters (AgNCs) via a one-step bioinspired approach and further exploited these as aptasensors for the detection of a trace antibiotic, bleomycin (BLM). Using FeFe Prussian blue (FeFe PB) as the core, a bimetallic CuFe@FeFe PBA layer was prepared by coupling with AgNCs synthesized by taking the BLM-targeted aptamer as a template (denoted by AgNCs/Apt@CuFe@FeFe). The coupling of AgNCs/Apt via a one-step bioinspired approach not only can improve the sensing performance of CuFe@FeFe-based aptasensors but also can shorten the aptasensor fabrication procedure. Due to the strong coordination interaction between abundant Fe(II) ions contained in CuFe@FeFe PBA nanospheres and BLM (represented by Fe(II)·BLM), the Fe(II)·BLM complex formed enables aptamer strands to undergo an irreversible cleavage event that can result in a significant change in electrochemical activity. Electrochemical results displayed that both CuFe@FeFe- and AgNCs/Apt@CuFe@FeFe-based aptasensors exhibited high sensitivity and selectivity, good stability and reproducibility, and acceptable applicability toward BLM. In comparison with the pristine CuFe@FeFe-based aptasensor (limit of detection (LOD) = 0.49 fg mL-1 within the BLM concentration from 1.0 to 2.0 ng mL-1), the as-prepared AgNCs/Apt@CuFe@FeFe-based aptasensor gave a extremely lower LOD value of 0.0082 fg mL-1 within a relatively narrow BLM concentration range (0.01 fg mL-1 to 0.1 pg mL-1). The proposed method can broaden the application of PBA nanomaterials in food safety and biosensing fields and provides a potential determination method for rapidly detecting BLM in various aqueous environments.

Cu x O@DNA sphere-based electrochemical bioassay for sensitive detection of Pb2.

The paper describes a one-step synthetic method to chemically reduce cupric sulfate by ascorbic acid in the presence of DNA strands to directly produce Cu x O@DNA spheres. The DNA strands act as template to assist the preparation of Cu x O, and also are capable of specifically binding  Pb(II) ions. The Cu x O@DNA spheres possess high specific surface area and strong bioaffinity. They can be directly employed as platform for detecting Pb2+ sensitively. Electrochemical impedance spectroscopy data showed that the assay exhibits high sensitivity and a wide linear analytical range that extends from 0.1 to 100 nM, and the detection limit is 6.8 pM at a signal-to-noise ratio of 3. The assay is selective, acceptably reproducible, stable, and well feasible for the detection of Pb2+ in blood serum. Graphical abstract Schematic presentation of the preparation of DNA-templated Cu x O spheres (Cu x O@DNA) for use in electrochemical detection of Pb2+. The assay exhibits detection limit of 6.8 pM, high selectivity, acceptable reproducibility, stability, and good applicability for Pb2+ detection.

Selective detection of silver ions using mushroom-like polyaniline and gold nanoparticle nanocomposite-based electrochemical DNA sensor.

A highly sensitive electrochemical DNA biosensor made of polyaniline (PANI) and gold nanoparticles (AuNPs) nanocomposite (AuNPs@PANI) has been used for the detection of trace concentration of Ag(+). In the presence of Ag(+), with the interaction of cytosine-Ag(+)-cytosine (C-Ag(+)-C), cytosine-rich DNA sequence immobilized onto the surface of AuNPs@PANI has a self-hybridization and then forms a duplex-like structure. The whole detection procedure of Ag(+) based on the developed biosensor was evaluated by electrochemical impedance spectroscopy. On semi-logarithmic plots of the log Ag(+) concentration versus peak current, the results show that the prepared biosensor can detect silver ions at a wide linear range of 0.01-100 nM (R = 0.9828) with a detection limit of 10 pM (signal/noise = 3). Moreover, the fabricated sensor exhibits good selectivity and repeatability. The detection of Ag(+) was determined by Ag(+) self-induced conformational change of DNA scaffold that involved only one oligonucleotide, showing its convenience and availability.

Multifunctional photocatalyst of graphitic carbon embedded with Fe2O3/Fe3O4 nanocrystals derived from lichen for efficient photodegradation of tetracycline and methyl blue.

We propose a feasible and economical method of constructing biomass-based multifunctional photocatalysts with excellent adsorption performance and high photodegradation abilities toward tetracycline (TC) and methyl blue (MB) under visible light. A series of novel hybrids of porous graphitic carbon embedded with Fe2O3/Fe3O4 nanocrystals (denoted as Fe2O3/Fe3O4@C) were derived from lichen doped with different dosages of Fe3+ by calcination at 700°C under a N2 atmosphere. The Fe2O3/Fe3O4@C hybrids exhibited nanoflake-like shapes, mesoporous structures, and efficient visible light harvesting, thus indicating enhanced adsorption ability and photoactivity toward pollutants. The formed Fe2O3/Fe3O4 heterojunction improved the separation efficiency and inhibited the recombination of photogenerated carriers, whereas the carbon network improved the transfer of photogenerated electrons. Under optimised conditions, the Fe2O3/Fe3O4@C-1 hybrid demonstrated enhanced photodegradation efficiencies of 96.4% for TC and 100% for MB under visible light. In addition, electron spin resonance and trapping measurements were performed to identify active species and determine the photocatalytic mechanism toward pollutants. •O2- and •OH were the active species involved, playing critical roles in the TC and MB photodegradation processes. In addition, a bacterium test revealed that the products of TC degradation by Fe2O3/Fe3O4@C-1 showed low biological toxicity. This work provides a promising preparation strategy or biomass-based photocatalysts for application in environmental pollutant treatment.

Confinement of defect-rich bimetallic In2O3/CeO2 nanocrystals in mesoporous nitrogen-doped carbon as a sensitive platform for photoelectrochemical aptasensing of Escherichia coli.

The sensitive determination of food-borne pathogens from food products is essential to ensure food safety and to protect people's health. Herein, a novel photoelectrochemical (PEC) aptasensor was manufactured based on defect-rich bimetallic cerium/indium oxide nanocrystals confined in mesoporous nitrogen-doped carbon (denoted as In2O3/CeO2@mNC) for sensitively detecting Escherichia coli (E. coli) from real samples. A new cerium-based polymer-metal-organic framework [polyMOF(Ce)] was synthesized using polyether polymer containing 1,4-benzenedicarboxylic acid unit (L8) as ligand, trimesic acid as co-ligand, and cerium ions as coordination centers. After adsorbing trace indium ions (In3+), the gained polyMOF(Ce)/In3+ complex was calcined at high temperature under nitrogen atmosphere, resulting in the production of a series of defect-rich In2O3/CeO2@mNC hybrids. Benefitting from the advantages of high specific surface area, large pore size, and multiple functionality of polyMOF(Ce), In2O3/CeO2@mNC hybrids showed enhanced visible light absorption ability, separation performance of the photo-generated electrons and holes, promoted electron transfer, as well as the strong bioaffinity toward E. coli-targeted aptamer. Accordingly, the constructed PEC aptasensor illustrated an ultralow detection limit of 1.12 CFU mL-1, remarkably lower than most of the reported E. coli biosensors, along with high stability and selectivity, excellent reproducibility, and expected regeneration ability. The present work provides insight into the construction of a general PEC biosensing strategy based on MOF-based derivatives for the sensitive analysis of food-borne pathogens.

Multiple active cobalt species embedded in microporous nitrogen-doped carbon network for the selective production of hydrogen peroxide.

To obtain excellent electrocatalysts for improving H2O2 yield and selectivity, we formulated a novel method for embedding cobalt catalytic active sites in porous two-dimensional nitrogen-doped carbon network (CNy) network and employed them as excellent two-electron oxygen reduction reaction (2e--ORR) electrocatalysts. The polymeric cobalt-based metal-organic framework (polyCo-MOF) and melamine-cyanuric acid-complex (MCA) hybrid (denoted as polyCo-MOF@MCA) was used as a precursor for preparing a series of electrocatalysts comprising multiple active sites such as metallic Co, CoOx, or Co-N, which are homogeneously embedded in the porous two-dimensional CNy network through pyrolysis at high temperatures (600 °C, 700 °C, and 800 °C) under N2 atmosphere. The obtained CoOx/Co@CNy,700 hybrid by pyrolyzing polyCo-MOF@MCA at 700 °C displayed remarkably high H2O2 production and large selectivity in an alkaline solution. The possible catalytic mechanism of CoOx/Co@CNy,700 toward 2e--ORR was identified by determining the catalytic kinetics and control experiments. The cathode assembled with the CoOx/Co@CNy,700 hybrid showed the maximum H2O2 production of 405 mmol L-1gcat.-1h-1 with a high Faradaic efficiency of 88.9 % at 0.65 V. The present work demonstrated a novel strategy for identifying excellent electrocatalysts with homogeneously dispersed multiple active sites and high production and selectivity for H2O2 synthesis, extending the applications of porous organic frameworks to the field of clean energy.

Hierarchical CoCoPBA@PCN-221 nanostructure for the highly sensitive detection of deoxynivalenol in foodstuffs.

An electrochemical impedimetric immunosensor was constructed based on a hierarchical nanostructured CoCo Prussian blue analogue entrapped by a Zr-based porphyrin MOF (denoted by CoCoPBA@PCN-221) for the sensitive detection of deoxynivalenol (DON). Given that CoCoPBA@PCN-221 demonstrated a hierarchical nanostructure, large specific surface area, and the synergistic effect between mixed metal valence states (Co2+/Co3+) and Zr clusters, it thus displayed a high binding interaction with the DON-targeted antibody. Compared with CoCoPBA and PCN-221, CoCoPBA@PCN-221 showed a superior stabilization ability toward the antibody-antigen complex in aqueous solution. Under optimum conditions, the CoCoPBA@PCN-221-based impedimetric immunosensor exhibited a good linear range from 1 fg mL-1 to 1 ng mL-1, and an ultralow detection limit of 0.14 fg mL-1, accompanied by high selectivity, reproducibility, stability, and applicability in foodstuffs. This method allows the integration of MOFs with cascading properties for applications in the biosensing and food safety fields.