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Acetaminophen (AC) is one of the most common over-the-counter drugs, and its pollutant in groundwater has attracted more attention due to its serious risk to human health. Currently, the research on AC is mainly focused on its detection, but few are concerned about its removal. In this work, for the first time, nitrogen-doped Soulangeana sepals derived biochar/β-cyclodextrin-Metal-organic frameworks (N-SC/β-CD-MOFs) composite was proposed for the simultaneous efficient removal and detection of AC. N-SC/β-CD-MOFs combined the properties of host-guest recognition of β-CD-MOFs and porous structure, high porosity, and large surface area of N-SC. Their synergies endowed N-SC/β-CD-MOFs with a high adsorption capacity toward AC, which was up to 66.43 mg/g. The adsorption type of AC on the surface of N-SC/β-CD-MOFs conformed to the Langmuir adsorption model, and the study of the adsorption mechanism showed that AC adsorption on N-SC was mainly achieved through hydrogen bonding. In addition, the high conductivity, large specific surface area and abundant active sites of N-SC/β-CD-MOFs were of great significance to the high-performance detection of AC. Accordingly, the sensor prepared with N-SC/β-CD-MOFs presented a wide linear range (1.0-30.0 μM) and a low limit of detection of 0.3 nM (S/N = 3). These excellent performances demonstrate that N-SC/β-CD-MOFs could act as an efficient dual-functional material for the detection and removal of AC.

Sensitive, selective, and real-time detection of nitric oxide (NO) is still challenging due to its rapid diffusion, short half-life, and low concentration in living systems. Herein, we synthesized well-defined ultralong metal-organic framework nanowires (MOFNWs) that were further uniformly covered with gold nanoparticle (AuNPs) and ionic liquids (ILs) and applied these NWs to detect and monitor NO released from living cells. In this system, ILs and AuNPs act as excellent catalysts for electrochemical oxidation of NO. By taking advantage of the synergetic effect between ILs, AuNPs and MOFNWs, the composite (IL@Au@MOFNWs) sensor probe displays excellent electrocatalytic activity toward NO oxidation with a detection limit as low as 2.28 nM for NO detection. The high levels of selectivity and sensitivity to NO in complex biological environments can be attributed to the exposed Ni 2+ active sites, high ion-electron transport rates of NWs, and the high conductivity of ILs and AuNPs. Furthermore, the IL@Au@MOFNWs offer a biocompatible sensing interface enabling rapid real-time monitoring of NO released from living cells by drug stimulation. Collectively, these results demonstrate that functionalized ultralong MOFNWs exhibit a remarkable ability to quantify NO levels in cells and could therefore provide new potential of this sensor in electrochemical detection of living bodies.

A ratiometric electrochemical biosensor based on a covalent organic framework (COF Thi-TFPB ) loaded with acetylcholinesterase (AChE) was developed. First, an electroactive COF Thi-TFPB with a two-dimensional sheet structure, positive charge and a pair of inert redox peaks was synthesized via a dehydration condensation reaction between positively charged thionine (Thi) and 1,3,5-triformylphenylbenzene (TFPB). The immobilization of AChE on the positively charged electrode surface was beneficial for maintaining its bioactivity and achieving the best catalytic effect; therefore, the positively charged COF Thi-TFPB was an appropriate support material for AChE. Furthermore, the COF Thi-TFPB provided a stable internal reference signal for the constructed AChE inhibition-based electrochemical biosensor to eliminate various effects which were unrelated to the detection of carbaryl. The sensor had a linear range of 2.2-60 μM with a detection limit of 0.22 μM, and exhibited satisfactory reproducibility, stability and anti-interference ability for the detection of carbaryl. This work offers a possibility for the application of COF-based materials in the detection of low-level pesticide residues.

Riboflavin (RF) is one of the necessary vitamins. If human body lacks RF, it will lead to inflammation and dysfunction of mouth, lips and skin. Thus sensitive and accurate determination of RF is necessary. Here, an electroactive covalent-organic framework nanobelt (COF TFPB-Thi ) with thickness of 1.4 nm was prepared by amine-aldehyde condensation reaction between thionine and 1, 3, 5-tris (p-formylphenyl) benzene, which was then grown vertically on three-dimensional porous carbon derived from kenaf stem (3D-KSC) for double signal ratiometric electrochemical detection of RF. The resulted 3D-KSC/COF TFPB-Thi showed two reduction peaks at -0.08 V and -0.23 V, which came from the reduction of COF TFPB-Thi and the conjugated structure of COF TFPB-Thi , respectively . In the presence of RF, those RF molecules near the electrode surface were oxidized at 0.6 V. Then some oxidized RF (RF ox ) adsorbed on COF TFPB-Thi would oxidize COF TFPB-Thi into COF TFPB-Thi (ox) while other RF ox adsorbed on 3D-KSC kept unchanged. When the potential was scanned from 0.6 V to -0.6 V, both COF TFPB-Thi (ox) and RF ox adsorbed on 3D-KSC were reduced at -0.08 V and -0.45 V accordingly, while the reduction peak of -0.23 V of the conjugated structure of COF TFPB-Thi kept constant. When j -0.45 /j -0.23 was used as the response signal, the detection limit was 44 nM and the linear range was 0.13 μM -0.23 mM. By using j -0.08 /j -0.23 as the response signal, a detection limit of 90 nM and a linear range of 0.30 μM-0.23 mM (S/N = 3) were obtained. By using double signals, the measurement results can be corrected to make the results more accurate and reliable. The sensor also showed good selectivity, reproducibility and stability, which provided a good application prospects., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Electrochemical biosensors based on enzymes modified electrode are attracting special attention due to their broad applications. However, the immobilization of enzymes on electrode is always an important challenge because it's not conducive to conformational expansion of enzymes and affects the bioactivity of enzymes accordingly. Although the imobilization of enzymes in micropores of crystalline covalent-organic framework (COF) and metal-organic framework (MOF) to construct electrochemical biosensors based on pore embedding can achive good reuslts, their micropores can still not guarantee that the enzyme's conformation is well extended. Herein, a multienzyme microcapsules (enzymes@COF) containing glucose oxidase, horseradish peroxidase and acetylcholinesterase with a 600 nm-sized cavity and a shell of COF was used to construct electrochemical biosensors. The 600 nm-sized cavity ensures free conformation expansion of encapsulated enzymes and the shell of COF with good chemical stablity protects encapsulated enzymes against external harsh environments. And the specific catalytic substrates of the enzymes can infiltrated into the microcapsule through the pores of COF shell. So, the biosensor based on enzymes@COF microcapsules demonstrated preeminent performances as compared with those of enzymes assembled on electrode. The detection limits were 0.85 μM, 2.81 nM, 3.0×10 -13  g/L, and the detection range were 2.83 μM-8.0 mM, 9.53 nM-7.0 μM, 10 -12  g/L-10 -8  g/L for glucose, H2O2 and malathion detection. This work shows that it is feasible to fabricate electrochemical sensors using enzymes@COF microcapsules., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Here, a novel iron-porphyrin-based covalent organic framework (COF p-Fepor NH2-BTA ) was synthesized and applied for electrochemical sensing H 2 O 2 and pH which involved in many biological processes. The COF p-Fepor NH2-BTA was obtained by post-modification of porphyrin-based COF (COF p-por NH2-BTA ) which was firstly synthesized by aldehyde-ammonia condensation reaction between 1,3,5-benzenetricarboxaldehyde and 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H- porphine. The COF p-por NH2-BTA was proved to be regular and uniform spherical particles with diameter about 1 μm, as well as possessed good crystalline structure and abundant micropores of about 1.4 nm. The resulted COF p-Fepor NH2-BTA after post-modification with Fe 2+ maintained the original shape and crystalline structure of COF p-por NH2-BTA , while the micropores decreased to be about 0.89 nm. Electrochemical results indicated that the synthesized COF p-Fepor NH2-BTA had good electrochemical redox and proton activity owing to iron-porphyrin, enabling to simultaneously be used as mimic peroxidase to catalyze the reduction of hydrogen peroxide (H 2 O 2 ) and evaluate pH using current and potential as signal, respectively. The prepared sensor showed good performance for H 2 O 2 detection from 6.85 nM to 7 μM with the detection limit of 2.06 nM (S/N = 3), and pH test from 3.0 to 9.0. This work demonstrated that the iron-porphyrin-based COF could be used as a mimic peroxidase to apply in biological fields., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Graphical abstract Highlights • Covalent organic framework with multiple redox-active states was used as electrochemical sensing platform. • The COF DHTA-TTA was synthesized by amine-aldehyde condensation reaction between TTA and DHTA. • COF DHTA-TTA was two-dimensional nanosheet with highly ordered crystal structure and mesopores. • A ratiometric electrochemical sensor was created based on COF DHTA-TTA to determine H 2 O 2 and pH. • A glucose biosensor was also created via using COF DHTA-TTA and exhibited excellent performances. Abstract Here, a covalent organic framework with multiple redox-active state synthesized by amine-aldehyde condensation reaction between 4,4′,4′'-(1,3,5-triazine-2,4,6-triyl) trianiline and 2,5-dihydroxy terethaldehyde (COF DHTA-TTA) was used as novel electrochemical sensing and biosensing platform at first time. The COF DHTA-TTA was demonstrated to be two-dimensional nanosheets with highly ordered conjugated structure and uniform mesopores about 3.67 nm. Electrochemical studies revealed that a ratiometric electrochemical sensor could be constructed by using COF DHTA-TTA itself as electroactive materials to determine hydrogen peroxide (H2O2) and pH level based on both current and potential signals. The single electrochemical sensor could monitor H2O2 concentration from 5.66 μM to 400 μM and pH level ranging from 11.0 to 3.0. Considering that the COF DHTA-TTA had good catalytic activity for oxygen reduction reaction in 0.2 M PBS (pH = 7.0), glucose oxidase was further loaded on COF DHTA-TTA via its nanosized pores and abundant active sites originated from N-doped skeleton, and the glucose biosensor exhibited good performances for glucose detection from 1.26 μM to 6.0 mM at −0.30 V, as well as from 0.60 μM to 6.0 mM at −0.53 V. The work provided good examples to construct electrochemical sensors based on redox-active COF. [ABSTRACT FROM AUTHOR]

A novel Ni@carbon nanocomposites/three-dimensional kenaf stem-derived macroporous carbon (3D-KSCs)-integrated electrode was prepared by calcinating Ni-benzenetricarboxylic acid (Ni-BTC) metal-organic frameworks (MOFs) grown on 3D-KSCs under N2 atmosphere for electrochemical glucose sensor. Both Ni-BTC MOFs/3D-KSCs and Ni@carbon nanocomposites/3D-KSCs-integrated electrode were studied by scanning electron microscopy and X-ray powder diffraction. These results showed that many flowerlike Ni-BTC MOFs which were composed of sticklike nanostructures were grown on the surface of 3D-KSCs. After calcination under N2 atmosphere, lots of pearl chain-like nanostructures were formed and uniformly arrayed on 3D-KSC electrode. XRD results confirmed that the Ni-BTC MOFs were successfully transformed into pearl chain-like Ni@carbon nanocomposites. Both electrochemical behaviors and electrocatalytic performances of Ni@carbon nanocomposites/3D-KSCs-integrated electrode were explored. Thanks to its large specific surface area, 3D macropores and special structures, the Ni@carbon nanocomposites/3D-KSCs-integrated electrode showed wide linear range (0.024-1.2 mM) and low detection limit (7.85 μM, S/N = 3) for glucose sensing. Noteworthily, the MOFs/3D-KSCs might be proposed to prepare other nanocomposites for electrochemical biosensing. [ABSTRACT FROM AUTHOR]

This study demonstrates the exploitation of carbon nanotubes (CNTs) combined with mesoporous metal-organic frameworks (Tb@mesoMOFs) to form a novel nanocomposite as the platform to construct electrochemical biosensors for glucose detection. Energy-dispersive X-ray spectroscopy, UV/Vis spectroscopy, scanning electron microscopy, and electrochemical techniques were used to characterize the Tb@mesoMOFs-CNT nanocomposites. The results showed that a thin layer of Tb@mesoMOFs uniformly covered the surface of CNTs. The Tb@mesoMOFs-CNT nanocomposites served as a supporting matrix to load both methylene green (MG) as electron mediators and glucose dehydrogenases (GDH) as electrocatalysts on a glassy carbon electrode (GCE) for constructing an electrochemical glucose biosensor, owing to the large number of micropores of Tb@mesoMOFs and excellent electrical conductivity of the CNTs together with ultrahigh surface area of the nanocomposites. GDH/MG−Tb@MOF-CNTs/GCE showed good performance for glucose detection with a wide linear range of approximately 25 μM to 17 mM and a low detection limit of 8 μM ( R=0.998, n=10). The work also provided a novel idea to prepare excellent MOFs/CNT-based materials for electrochemical sensing. [ABSTRACT FROM AUTHOR]