An intriguing electrochemical impedance aptasensor based on a porous organic framework supported silver nanoparticles for ultrasensitively detecting theophylline

State-of-the-art electrochemical biosensors based on covalent organic frameworks and their hybrid materials

As the development of global population and industry civilization, the accurate and sensitive detection of intended analytes is becoming an important and great challenge in the field of environmental, medical, and public safety. Recently, electrochemical biosensors have been constructed and used in sensing fields, such as antibiotics, pesticides, specific markers of cancer, and so on. Functional materials have been designed and prepared to enhance detection performance. Among all reported materials, covalent organic frameworks (COFs) are emerging as porous crystalline materials to construct electrochemical biosensors, because COFs have many unique advantages, including large surface area, high stability, atom-level designability, and diversity, to achieve a far better sensing performance. In this comprehensive review, we not only summarize state-of-the-art electrochemical biosensors based on COFs and their hybrid materials but also highlight and discuss some typical examples in detail. We finally provide the challenge and future perspective of COFs-based electrochemical biosensors.

Integrating porphyrin-based nanoporous organic polymers with electrochemical aptasensors for ultratrace detection of kanamycin

The synthesis and characterization of two new porphyrin-based porous organic polymers (POPs) via Sonogashira cross-coupling reaction and leverage the two obtained POPs is reported for the fabrication of electrochemical aptasensors to detect kanamycin at an ultratrace level. The resultant electrochemical aptasensor demonstrates a high linear relationship with the logarithmic value of kanamycin concentration in the range 5 × 10-5-5 μg/L with the limit of detection of 17.6 pg/L or 36.3 fM. During the analysis of real samples from milk and river, a relative standard deviation of less than 4.39%, and good recovery values in the range 97.0-105% were obtained.

Flexible electrode-based voltammetric detection of Y (III) ions in real water samples using an efficient CyDTA complexing strategy

The rapid detection of rare earth elements is crucial in various fields, such as materials science, biomedicine, and water quality assessment. However, no studies have reported on the detection of yttrium (Y) using electrochemical sensor-based devices. In this study, we present an innovative method for detecting Y(III) ions in aquatic environments using an electroanalytical detection platform. We have developed a complexation catalytic method that integrates trans-1,2-cyclohexanediaminetetraacetic acid (CyDTA) and silver nanoparticles (Ag NPs), thereby enhancing the adsorption and electrochemical response of Y(III) ions. The modified electrode demonstrates an 18-fold increase in the response signal of the Y(III) reduction peak compared to the bare LIG electrode. To elucidate the electrocatalytic mechanism, we conducted various interface characterization methods and DFT simulations. The Ag-CyDTA/LIG electrode exhibits excellent detection performance, with a broad linear dynamic range of 1 × 10-6 to 0.01 g/L and an exceptionally low detection limit of 0.02 μg/L. Significantly, we successfully employed the electrochemical sensing platform to analyze real water samples from rare earth ore, marking the first report on the voltammetric detection of Y(III) ions in real water samples using a flexible electrode. These findings offer a promising technical solution for the practical detection of Y(III) ions.

One-step self-assembly of Fe-biochar composite for enhanced persulfate activation to phenol degradation: Different active sites-induced radical/non-radical mechanism

Persulfate (PS) activation by nanoscale zerovalent iron (nZVI) is promising for water purification, while is limited due to its easy agglomeration and oxidation. Herein, nZVI encapsuled in carbon matrix shell was synthesized via one-step carbothermal reduction. The core-shell structure effectively inhibited oxidation and agglomeration of nZVI core, and graphitized porous structures facilitated phenol binding with maximal adsorption capacity of 117.10 mg/g achieved by nZVI_0.6-BC₈₀₀. Both reactive oxygen species (SO₄^•-, O•H, O₂^•- and ¹O₂) and electron transfer process resulted in phenol decomposition. Owing to diversified active sites, the nZVI_0.6-BC₈₀₀/PS system could completely degrade phenol degradation within short time, and exhibited great adaptation to extensive pH range (3.0-9.0) and coexisting substances. Additionally, the nZVI_0.6-BC₈₀₀/PS system could maintain over 85% removal of phenol after three recycles or 50 days of storage, and was highly-efficient to different water environments, thus proposing rational design of iron-carbon catalyst with potential in water treatment.

Advancements in nanomaterial-based aptasensors for the detection of emerging organic pollutants in environmental and biological samples

The combination of nanomaterials (NMs) and aptamers into aptasensors enables highly specific and sensitive detection of diverse pollutants. The great potential of aptasensors is recognized for the detection of diverse emerging organic pollutants (EOPs) in different environmental and biological matrices. In addition to high sensitivity and selectivity, NM-based aptasensors have many other advantages such as portability, miniaturization, facile use, and affordability. This work showcases the recent advances achieved in the design and fabrication of NM-based aptasensors for monitoring EOPs (e.g., hormones, phenolic contaminants, pesticides, and pharmaceuticals). On the basis of their sensing mechanisms, the covered aptasensing systems are classified as electrochemical, colorimetric, PEC, fluorescence, SERS, and ECL. Special attention has been paid to the fabrication processes, analytical achievements, and sensing mechanisms of NM-based aptasensors. Further, the practical utility of aptasensing approaches has also been assessed based on their basic performance metrics (e.g., detection limits, sensing ranges, and response times).

Paper-based analytical device coupled with Bi-MOF: Electric field amplification and fluorescence sensing of glyphosate

Glyphosate, a potent herbicide wildly used in the world, involves potential hazards to human health by accumulating in the food chain. Due to its absence of chromophores and fluorophores, the rapid visual detection of glyphosate has always been difficult. Herein, a paper-based geometric field amplification device visualized by the amino-functionalized bismuth-based metal-organic framework (NH₂-Bi-MOF) was constructed for sensitive fluorescence determination of glyphosate. Fluorescence of the synthesized NH₂-Bi-MOF was immediately enhanced by interaction with glyphosate. The field amplification of glyphosate was implemented by coordinating the electric field and the electroosmotic flow, which was orchestrated by the geometric configuration of paper channel and the concentration of polyvinyl pyrrolidone, respectively. Under the optimal conditions, the developed method exhibited a linear range of 0.80-200 μmol L^-1 with about 12500-fold signal enhancement achieved by just 100 s electric field amplification. It was applied to soil and water with recoveries between 95.7% and 105.6%, holding great prospects in on-site analysis of hazardous anions for environment safety.

Design and Construction of an Azo-Functionalized POP for Reversibly Stimuli-Responsive CO2 Adsorption

A porous azo-functionalized organic polymer (JJU-2) was designed and prepared via oxidative coupling polymerization promoted by FeCl3. JJU-2 exhibited reversibly stimuli-responsive CO2 adsorption properties as a result of the trans/cis isomerization of the polymer’s azo-functionalized skeleton. Under UV irradiation and heat treatment, this porous material displayed various porous structures and CO2 adsorption properties. The initial Brunauer-Emmett-Teller (BET) surface area of JJU-1 is 888 m2 g−1. After UV irradiation, the BET surface area decreases to 864 m2 g−1, along with the decrease of micropores around 0.50 nm and 1.27 nm during the trans-to-cis isomerization process. In addition, CO2 sorption isotherms demonstrate an 8%t decrease, and the calculated Qst of CO2 has decreased from 29.0 kJ mol−1 to 26.5 kJ mol−1 due to the trans to cis conversion of the azobenzene side group. It is noteworthy that JJU-2′s CO2 uptakes are nearly constant over three cycles of alternating external stimuli. Therefore, this azo-functionalized porous material was a potential carbon capture material that was responsive to stimuli.

Advances in Biosensing of Chemical Food Contaminants Based on the MOFs-Graphene Nanohybrids

Food safety issue is becoming an international challenge for human health owing to the presence of contaminants. In this context, reliable, rapid, and sensitive detecting technology is extremely demanded to establish food safety assurance systems. MOFs (Metal-organic frameworks) are a new type of porous crystalline material with particular physical and chemical characteristics presented in food safety requirements. (Bio)sensors driven MOF materials have emerged as a promising alternative and complementary analytical techniques, owing to their great specific area, high porosity, and uniform and fine-tunable pore buildings. Nevertheless, the insufficient stability and electrical conductivity of classical MOFs limit their utilization. Employing graphene-derived nanomaterials with high functional elements as patterns for the MOF materials not only improves the structural instability and poor conductivity but also impedes the restacking and aggregation between graphene layers, thus significantly extending the MOFs application. A review of MOFs-graphene-based material used in food contamination detection is urgently needed for encouraging the advance of this field. Herein, this paper systematically outlines current breakthroughs in MOF-graphene-based nanoprobes, outlines their principles, and illustrates their employments in identifying mycotoxins, heavy metal ions, pathogens, antibiotics, and pesticides, referring to their multiplexing and sensitivity ability. The challenges and limitations of applying MOF-graphene composite for precise and efficient assessment of food were also debated. This paper would maybe offer some inspired concepts for an upcoming study on MOF-based composites in the food security context.

Electrochemical Aptasensing of SARS-CoV-2 Based on Triangular Prism DNA Nanostructures and Dumbbell Hybridization Chain Reaction

Development of convenient, accurate, and sensitive methods for rapid screening of severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infection is highly desired. In this study, we have developed a facile electrochemical aptasensor for the detection of the SARS-CoV-2 S1 protein amplified by dumbbell hybridization chain reaction (DHCR). A triangular prism DNA (TPDNA) nanostructure is first assembled and modified at the electrode interface. Due to the multiple thiol anchors, the immobilization is quite stable. The TPDNA nanostructure also provides an excellent scaffold for better molecular recognition efficiency on the top single-strand region (DHP0). The aptamer sequence toward the SARS-CoV-2 S1 protein is previously localized by partial hybridization with DHP0. In the presence of the target protein, the aptamer sequence is displaced and DHP0 is exposed. After further introduction of the fuel stands of DHCR, compressed DNA linear assembly occurs, and the product can be stacked on the TPDNA nanostructure for the enrichment of electrochemical species. This electrochemical method successfully detects the target protein in clinical samples, which provides a simple, robust, and accurate platform with great potential utility.

An Azo-Group-Functionalized Porous Aromatic Framework for Achieving Highly Efficient Capture of Iodine

The strong radioactivity of iodine compounds derived from nuclear power plant wastes has motivated the development of highly efficient adsorbents. Porous aromatic frameworks (PAFs) have attracted much attention due to their low density and diverse structure. In this work, an azo group containing PAF solid, denoted as LNU-58, was prepared through Suzuki polymerization of tris-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-phenyl)-amine and 3,5-dibromoazobenzene building monomers. Based on the specific polarity properities of the azo groups, the electron-rich aromatic fragments in the hierarchical architecture efficiently capture iodine molecules with an adsorption capacity of 3533.11 mg g−1 (353 wt%) for gaseous iodine and 903.6 mg g−1 (90 wt%) for dissolved iodine. The iodine uptake per specific surface area up to 8.55 wt% m−2 g−1 achieves the highest level among all porous adsorbents. This work illustrates the successful preparation of a new type of porous adsorbent that is expected to be applied in the field of practical iodine adsorption.

Integrating a Luminescent Porous Aromatic Framework into Indicator Papers for Facile, Rapid, and Selective Detection of Nitro Compounds

Porous aromatic framework materials with high stability, sensitivity, and selectivity have great potential to provide new sensors for optoelectronic/fluorescent probe devices. In this work, a luminescent porous aromatic framework material (LNU-23) was synthesized via the palladium-catalyzed Suzuki cross-coupling reaction of tetrabromopyrene and 1,2-bisphenyldiborate pinacol ester. The resulting PAF solid exhibited strong fluorescence emission with a quantum yield of 18.31%, showing excellent light and heat stability. Because the lowest unoccupied molecular orbital (LUMO) of LNU-23 was higher than that of the nitro compounds, there was an energy transfer from the excited LNU-23 to the analyte, leading to the selective fluorescence quenching with a limit of detection (LOD) ≈ 1.47 × 10⁻⁵ M. After integrating the luminescent PAF powder on the paper by a simple dipping method, the indicator papers revealed a fast fluorescence response to gaseous nitrobenzene within 10 s, which shows great potential in outdoor fluorescence detection of nitro compounds.

Introducing Polar Groups in Porous Aromatic Framework for Achieving High Capacity of Organic Molecules and Enhanced Self-Cleaning Applications

Due to the frequent oil/organic solvent leakage, efficient oil/water separation has attracted extensive concern. However, conventional porous materials possess nonpolar building units, which reveal relatively weak affinity for polar organic molecules. Here, two different polarities of superhydrophobic porous aromatic frameworks (PAFs) were synthesized with respective orthoposition and paraposition C=O groups in the PAF linkers. The conjugated structure formed by a large number of alkynyl and benzene ring structures enabled porous and superhydrophobic quality of PAFs. After the successful preparation of the PAF solids, PAF powders were coated on polyester fabrics by a simple dip-coating method, which endowed the resulting polyester fabrics with superhydrophobicity, porosity, and excellent stability. Based on the unique structure, the oil/water separation efficiency of two superhydrophobic flexible fabrics was more than 90% for various organic solvents. Polar LNU-26 PAF showed better separation performance for the polar oils. This work takes the lead in adopting the polar groups as building units for the preparation of porous networks, which has great guiding significance for the construction of advanced oil/water separation materials.

Metal-Organic Framework Accelerated One-Step Capture and Reduction of Palladium to Catalytically Active Nanoparticles

Recovery of noble metals and in situ transforming to functional materials hold great promise in the sustainability of natural resources but remain as a challenge. Herein, the variable chemical microenvironments created by the inorganic-organic hybrid composition of metal-organic frameworks (MOFs) were exploited to tune the metal-support interactions, thus establishing an integrated strategy for recovering and reducing palladium (Pd). Assisted by sonic waves and alcoholic solvent, selective capture of Pd(II) from a complicated matrix to directly afford Pd nanoparticles (NPs) in MOFs can be achieved in one step within several minutes. Mechanism investigation reveals that the Pd binding site and the energy barriers between ionic and metallic status are sensitive to chemical environments in different frameworks. Thanks to the clean, dispersive, and uniform nature of Pd NPs, Pd@MOFs synthesized from a complicated environment exhibited high catalytic activity toward 4-nitrophenol reduction and Suzuki coupling reactions.

Recent advances in metal/covalent organic framework-based electrochemical aptasensors for biosensing applications

The booming development of novel porous materials, metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) has been attracting a lot of attention due to their designabilities, diversities, and extensive applications. MOFs and COFs provide a new potential opportunity and platform to fabricate electrochemical aptasensors for biosensing applications. Compared to other traditional materials, MOF/COF-based electrochemical biosensors can appreciably amplify the electrochemical response signals to improve the sensing performance. Herein, we provide a comprehensive overview of MOF/COF-based electrochemical aptasensors for monitoring different ultra-trace analytes (e.g. antibiotics, pesticides, and cancer markers). This review systematically discusses the classification of electrochemical aptasensors based on various functional materials, including pure MOFs, MOF/conductive composites, metal nanoparticle/MOF composites, pure COFs, COFs/conductive composites, and other hybrid materials. Furthermore, some typical MOF/COF-based electrochemical aptasensors in the recognition of specific targets are described in detail to improve and guide further research for biosensing applications.

A Carbazole-Functionalized Porous Aromatic Framework for Enhancing Volatile Iodine Capture via Lewis Electron Pairing

Nitrogen-rich porous networks with additional polarity and basicity may serve as effective adsorbents for the Lewis electron pairing of iodine molecules. Herein a carbazole-functionalized porous aromatic framework (PAF) was synthesized through a Sonogashira-Hagihara cross-coupling polymerization of 1,3,5-triethynylbenzene and 2,7-dibromocarbazole building monomers. The resulting solid with a high nitrogen content incorporated the Lewis electron pairing effect into a π-conjugated nano-cavity, leading to an ultrahigh binding capability for iodine molecules. The iodine uptake per specific surface area was ~8 mg m-2 which achieved the highest level among all reported I2 adsorbents, surpassing that of the pure biphenyl-based PAF sample by ca. 30 times. Our study illustrated a new possibility for introducing electron-rich building units into the design and synthesis of porous adsorbents for effective capture and removal of volatile iodine from nuclear waste and leakage.

Rational Construction of a Responsive Azo-Functionalized Porous Organic Framework for CO2 Sorption

An azo-functionalized porous organic framework (denoted as JJU-1) was synthesized via FeCl3-promoted oxidative coupling polymerization. By virtue of a porous skeleton and a light/heat responsive azo functional group, this task-specific JJU-1 displays a reversible stimuli-responsive adsorption property triggered by UV irradiation and heat treatment. The initial Brunauer-Emmet-Teller (BET) surface area of this porous material is 467 m2 g-1. The CO2 sorption isotherms exhibit a slight decrease after UV irradiation because of the trans to cis conversion of the azo functional skeleton. It is worth mentioning that the responsive CO2 adsorption performance can be recycled for three cycles via alternating external stimuli, confirming the excellently reversible switchability of trans-to-cis isomerization and controllable CO2 adsorption.