Recent advances in the construction of functionalized covalent organic frameworks and their applications to sensing

Nanozymes meet hydrogels: Fabrication, progressive applications, and perspectives

Nanozyme, a class of emerging enzyme mimics, is the nanomaterials with enzyme-mimicking activity, which has obtained significant and widespread applications in various fields. However, they still face many challenges in practical applications (e.g., instability and low biocompatibility in the physiological environments), which affect their widespread applications to a certain extent. Hydrogels with superior performances (e.g., the controllable degradability, good biocompatibility, hydrophilic properties, and adjustable physical properties) may provide a promising strategy to make up the existing deficiencies of nanozymes in practical applications. Thus, the sapiential combination of nanozymes with hydrogels endows nanozyme hydrogels with both characteristics of nanozymes and properties of hydrogels, making nanozyme hydrogels become novel multifunctional materials. In this review, we comprehensively summarizes the preparation, properties, and progressive applications of nanozyme hydrogels. First of all, the main design and preparation strategies of nanozyme hydrogels are considerately summarized. Then, the properties of different nanozyme hydrogels are introduced. In addition, sophisticated applications of nanozyme hydrogels in the fields of biosensing, biomedicine applications, and environmental are comprehensively summarized. Most importantly, future obstacles and chances in this emerging field are profoundly proposed. This review will provide a new horizon for the development and future applications of novel nanozyme hydrogels.

Applications of covalent organic frameworks (COFs)-based sensors for food safety: Synthetic strategies, characteristics and current state-of-art

Food safety is a pressing global public issue that has garnered significant attention worldwide, especially recent outbreaks of foodborne illnesses. The use of emerging porous materials enables the development of effective and durable detection methods for the detection of food contaminants. Covalent organic frameworks (COFs), as a class of emerging porous crystalline materials, rendered with the advantage of large specific surface area, highly controllable and ordered structures, diverse pore structures, high stability, and controllable surface functionalization. Especially in the development of sensors, COFs exhibit versatile roles as signal amplifiers, molecular recognizers, molecular transfer mediators, carriers, catalysts, and reporters, making them highly valuable in various applications. In the context of food safety, COFs-based sensing platforms have shown great potential. This review aims to provide an in-depth understanding of COFs-based sensors by discussing recent advancements in this field. It begins with a systemic introduction of the synthetic strategies of COFs and the pros and cons, followed by the distinctive characteristics of COFs and their diverse functional roles in sensing strategies, emphasizing their importance in analysing food safety risks. Then the review further presented a comprehensive summary of the applications of COFs in sensing, specifically highlighting significant breakthroughs in the detection of various food contaminants like foodborne pathogens, mycotoxins, pesticides, antibiotics, heavy metals, etc. Additionally, the review addressed the challenges and opportunities associated with COFs-based sensors in the detection of food safety issues. The aim of the review was to contribute to the ongoing development and advancement of COFs for ensuring food safety.

A review of research progress on COF-based biosensors in pathogen detection

Despite the availability of various detection tools, the rapid identification and accurate detection of pathogens remain a major challenge in public health management. Covalent organic frameworks (COFs), which are crystalline conjugated organic polymers with considerable application potential, offer unique advantages in several fields owing to their highly ordered structure, large specific surface area, stable chemical properties, and tunable pore microenvironment. In recent years, with the rapid development of biosensing technology, COF application in the field of pathogen detection has attracted extensive attention. Herein, the properties, applications, and synthesis methods of COFs are briefly described, and the application types and basic principles of COFs in building an efficient and sensitive pathogen detection platform are emphatically discussed. Overall, we analyze the current challenges associated with COF-based biosensors in pathogen detection and look forward to their broad application prospects in biomedicine and public health in future.

Covalent organic frameworks in cancer theranostics: advancing biomarker detection and tumor-targeted therapy

In recent years, covalent organic frameworks (COFs) have garnered considerable attention in the field of onco-nanotechnology as a new type of nanoporous construct due to their promising physicochemical properties, ease of modification, and ability to be coupled with several moieties and therapeutic molecules. They can not only be used as biocompatible nanocarriers to deliver therapeutic payloads to the tumor zone selectively but can also be combined with a variety of therapeutic modalities to achieve the desired treatments. This review comprehensively presented recent achievements and progress in COF-based cancer diagnosis, detection, and cancer therapy to provide a better prospect for further research. Herein our primary emphasis lies on exploring the application of COFs as potential sensors for cancer-derived biomarkers that have received comparatively less attention in previous discussions. While the utilization of COFs in solid tumor therapy has faced significant challenges in scientific research and clinical applications, we reviewed the most promising features that underscore their potential in cancer theranostics.

Computational Screening Guiding the Development of a Covalent-Organic Framework-Based Gas Sensor for Early Detection of Lithium-Ion Battery Electrolyte Leakage

This study presents a computationally guided approach for selecting covalent organic frameworks (COFs) for the selective detection of the trace ethylene carbonate (EC) vapor, a key indicator of electrolyte leakage from lithium-ion batteries (LIBs). High-throughput screening, employing grand canonical Monte Carlo (GCMC) simulation complemented by density functional theory (DFT) calculations, was used to identify potential COF candidates from the CURATED COF database. Among the screened materials, an imine COF functionalized with quaternary ammonium (QA) groups, named COF-QA-4, exhibited a high adsorption capacity (5.88 mmol/g) and selectivity of EC vapor. DFT analysis revealed strong molecular interactions driven by a partial charge transfer mechanism between EC and the COF-QA-4 framework, underpinning its superior adsorption properties. Experimental validation through chemiresistive gas sensors fabricated with COF-QA-4 demonstrated excellent sensitivity and reversibility to 1.15 ppmv of EC vapor, maintaining consistent performance over three response-recovery cycles. This work highlights the potential of computationally guided material discovery for advancing sensor technologies in LIB safety monitoring.

Rational Design of Covalent Organic Frameworks for Photocatalytic Hydrogen Peroxide Production

Photocatalytic production of hydrogen peroxide (H2O2) represents a significant approach to achieving sustainable energy generation through solar energy, addressing both energy shortages and environmental pollution. Among various photocatalytic materials, covalent organic frameworks (COFs) have gained widespread attention and in-depth research due to their unique advantages, including high porosity, predesignability, and atomic-level tunability. In recent years, significant progress has been made in the development, performance enhancement, and mechanistic understanding of COF-based photocatalysts. This review focuses on the latest advancements in photocatalytic H2O2 production using COFs, particularly emphasizing the rational design of COF structures to regulate catalytic performance and exploring the fundamental processes involved in photocatalysis. Based on current research achievements in this field, this paper also discusses existing challenges and future opportunities, aiming to provide a reference for the application of COFs in photocatalytic H2O2 production.

Postbiotic-biosynthesized silver nanoparticles anchored on covalent organic frameworks integrated into carboxymethyl chitosan-based film for enhancing antibacterial packaging

Food packaging plays a vital role in guaranteeing the quality and safety of fresh products during the storage and distribution. Carboxymethyl chitosan (CMCS) is identified as a promising polymer for food packaging film owing to its film-forming ability, non-toxicity, and biodegradability. Nevertheless, the practical applications of pure CMCS film usually suffer from some limits owing to its poor antibacterial effect and mechanical strength. In this study, postbiotic-biosynthesized silver nanoparticles (AgNPs) anchored on covalent organic frameworks (COF) (namely COF-AgNP) were integrated into the CMCS film to enhance antibacterial packaging performance for preservation of fruits. Utilizing postbiotic as a reducing agent, COF-AgNPs composite nanomaterials were prepared by anchoring AgNPs on COF via in-situ reduction of Ag+. Furthermore, antibacterial packaging film was prepared using CMCS and COF-AgNPs (CMCS@COF-AgNPs) via a solution-casting method. Furthermore, characterization results proved that mechanical strength of CMCS@COF-AgNP films exhibited a gradual enhancement with the increased COFs-AgNPs content. Moreover, CMCS@COF-AgNP films exhibited an enhanced antibacterial activity and excellent biocompatibility. Importantly, CMCS@COF-AgNP coating can effectively preserve citrus quality and prolong its storage time. Therefore, CMCS@COF-AgNP films could be used as a promising and economically viable solution to diminish postharvest losses and prolong the shelf life of fresh products.

Cancer treatment approaches within the frame of hyperthermia, drug delivery systems, and biosensors: concepts and future potentials

This work presents a review of the therapeutic modalities and approaches for cancer treatment. A brief overview of the traditional treatment routes is presented in the introduction together with their reported side effects. A combination of the traditional approaches was reported to demonstrate an effective therapy until a few decades ago. With the improvement in the fabrication of nanomaterials, targeted therapy represents a novel therapeutic approach. This improvement established on nanoparticles is categorized into hyperthermia, drug delivery systems, and biosensors. Hyperthermia presents a personalized medicine-based approach in which targeted zones are heated up until the diseased tissue is destroyed by the thermal effect. The use of magnetic nanoparticles further improved the effectiveness of hyperthermia owing to the enhanced heating action, further increasing the accuracy of the targeting process. Nanoparticle-based biosensors present a smart nanodevice that can detect, monitor, and target tumor tissues by following the biomarkers in the body fluids. Magnetic nanoparticles offer a controlled thermo-responsive device that can be manipulated by changing the magnetic field, offering a more personalized and controlled hyperthermia therapeutic modality. Similarly, gold nanoparticles offer an effective aid in the hyperthermia treatment approach. Furthermore, carbon nanotubes and metal-organic frameworks present a cutting-edge approach to cancer treatment. A combination of functionalized nanoparticles offers a unique route for drug delivery systems, in which therapeutic agents carried by nanoparticles are guided into the human body and then released in the target spot.

Unveiling the catalytic potency of a novel hydrazone-linked covalent organic framework for the highly efficient one-pot synthesis of 1,2,4-triazolidine-3-thiones

A novel hydrazone-linked covalent organic framework (TRIPOD-DHTH COF) was synthesized through the ultrasonic treatment of 2,5-dihydroxyterephthalohydrazide (DHTH) and 4,4',4''-[1,3,5-triazine-2,4,6-triyltris(oxy)]tris-benzaldehyde (TRIPOD). The COF was extensively analyzed using FT-IR, PXRD, SEM, TEM, BET, XPS, TGA, and DTA techniques. The characterization studies revealed the presence of mesoporous properties and high thermal stability, with a surface area measuring 2.78 m2 g-1 and an average pore size of 8.88 nm. The developed COF demonstrated exceptional catalytic activity in synthesizing 1,2,4-triazolidine-3-thiones from thiosemicarbazide and various ketones and aldehydes using a water : ethanol (1 : 2) medium at room temperature. A significant yield (80-98%) of 1,2,4-triazolidine-3-thiones was obtained in a low reaction time (4-20 min). The role of TRIPOD as a precursor in the synthesis of the COF and as a reactant in the synthesis of 1,2,4-triazolidine-3-thione (3l) was found to be fascinating. The synthesized COF maintained its catalytic activity over eight runs, underscoring its efficiency and reusability, highlighting its potential for sustainable chemical syntheses.

Fast detection of tryptamine in meat products with azide-functionalized covalent organic frameworks confined in molecularly imprinted polymers

Tryptamine is a biogenic amine that affects organoleptic quality through the generation of off-odours in foods. Herein, imine-based covalent organic frameworks (COFs) were synthesized via Schiff base reactions and postmodified with click chemistry to generate azide-functionalized COFs with tunable azide units on the walls. The combination of molecular imprinting with COFs enabled the specific recognition of the targets. The resulting optosensing system (azide-functionalized COFs@MIPs) was used as a sample-to-answer analyser for detecting tryptamine (detection time within 10 min). A linear relationship was observed for the fluorescence response to tryptamine concentrations in the range of 3-120 μg L-1, with a limit of detection of 1.74 μg L-1. The recoveries for spiked samples were satisfactory, with relative standard deviations <9.90%. The optosensing system is a potential tool for the quantitative detection of tryptamine in meat products because of its lower cost, shorter processing time, and simpler processing steps compared to conventional chromatographic techniques.

A Machine Learning-Driven Surface-Enhanced Raman Scattering Analysis Platform for the Label-Free Detection and Identification of Gastric Lesions

Background

Gastric lesions pose significant clinical challenges due to their varying degrees of malignancy and difficulty in early diagnosis. Early and accurate detection of these lesions is crucial for effective treatment and improved patient outcomes.

Methods

This paper proposed a label-free and highly sensitive classification method for serum of patients with different degrees of gastric lesions by combining surface-enhanced Raman scattering (SERS) and machine learning analysis. Specifically, we prepared Au lotus-shaped (AuLS) nanoarrays substrates using seed-mediated and liquid-liquid interface self-assembly method for measuring SERS spectra of serum, and then the collected spectra were processed by principal component analysis (PCA) - multi-local means based nearest neighbor (MLMNN) model to achieve differentiation.

Results

By employing this pattern analysis, AuLS nanoarray substrates can achieve fast, sensitive, and label-free serum spectral detection. The classification accuracy can reach 97.5%, the sensitivity is higher than 96.7%, and the specificity is higher than 95.0%. Moreover, by analyzing the PCs loading plots, the most critical spectral features distinguishing different degrees of gastric lesions were successfully captured.

Conclusion

This discovery lays the foundation for combining SERS with machine learning for real-time diagnosis and recognition of gastric lesions.

Covalent-Organic Frameworks for Selective and Sensitive Detection of Antibiotics from Water

As the consumption of antibiotics rises, they have generated some negative impacts on organisms and the environment because they are often unable to be effectively degraded, and seeking effective detection methods is currently a challenge. Covalent-organic frameworks (COFs) are new types of crystalline porous crystals created based on the strong covalent interactions between blocked monomers, and COFs demonstrate great potential in the detection of antibiotics from aqueous solutions because of their large surface area, adjustable porosity, recyclability, and predictable structure. This review aims to present state-of-the-art insights into COFs (properties, classification, synthesis methods, and functionalization). The key mechanisms for the detection of antibiotics and the application performance of COFs in the detection of antibiotics from water are also discussed, followed by the challenges and opportunities for COFs in future research.

Conjugated molecularly imprinted polymers based on covalent organic frameworks: Fluorescent sensing platform for specific capture of urea and elimination of ethyl carbamate

This study described the preparation of an azide covalent organic framework-embedded molecularly imprinted polymers (COFs(azide)@MIPs) platform for urea adsorption and indirect ethyl carbamate (EC) removal from Chinese yellow rice wine (Huangjiu). By modifying the pore surface of COFs using the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction, COFs(azide) with a high fluorescence quantum yield and particular recognition ability were inventively produced. In order to selectively trap urea, the COFs(azide) were encased in an imprinted shell layer via imprinting technology. With a detection limit (LOD) of 0.016 μg L-1 (R2 = 0.9874), the COFs(azides)@MIPs demonstrated a good linear relationship with urea in the linear range of 0-5 μg L-1. Using real Huangjiu samples, the spiking recovery trials showed the viability of this sensing platform with recoveries ranging from 88.44 % to 109.26 % and an RSD of less than 3.40 %. The Huangjiu processing model system achieved 38.93 % EC reduction by COFs(azides)@MIPs. This research will open up new avenues for the treatment of health problems associated with fermented alcoholic beverages, particularly Huangjiu, while also capturing and removing hazards coming from food.

Magnetic covalent organic frameworks as sorbents in the chromatographic analysis of environmental organic pollutants

Covalent organic frameworks (COFs) are featured with large specific surface areas, good thermal stability, and abundant pores. These properties are exactly what the sorbents used for extraction or adsorption of interest substances are desired with. While, the low density and hydrophobicity of COFs often makes them difficult to be dispersed evenly and recovered from the aqueous solution. Magnetic covalent organic frameworks (MCOFs) inherit magnetic property of the magnetic particles and porous structure of COFs. They have improved dispersity in aqueous solution and phase separation can be rapidly achieved via external magnetic fields. This review summarized the synthesis strategies for MCOFs, and their application in trace environmental organic pollutants analysis by chromatography techniques. The selection of COFs types and modification with active groups for a certain adsorption purpose is discussed, along with the exploration of adsorption mechanisms, which is beneficial for the design and synthesis of MCOFs.

Fluorescent chemosensors facilitate the visualization of plant health and their living environment in sustainable agriculture

Globally, 91% of plant production encounters diverse environmental stresses that adversely affect their growth, leading to severe yield losses of 50-60%. In this case, monitoring the connection between the environment and plant health can balance population demands with environmental protection and resource distribution. Fluorescent chemosensors have shown great progress in monitoring the health and environment of plants due to their high sensitivity and biocompatibility. However, to date, no comprehensive analysis and systematic summary of fluorescent chemosensors used in monitoring the correlation between plant health and their environment have been reported. Thus, herein, we summarize the current fluorescent chemosensors ranging from their design strategies to applications in monitoring plant-environment interaction processes. First, we highlight the types of fluorescent chemosensors with design strategies to resolve the bottlenecks encountered in monitoring the health and living environment of plants. In addition, the applications of fluorescent small-molecule, nano and supramolecular chemosensors in the visualization of the health and living environment of plants are discussed. Finally, the major challenges and perspectives in this field are presented. This work will provide guidance for the design of efficient fluorescent chemosensors to monitor plant health, and then promote sustainable agricultural development.

Hydrazone-linked covalent organic framework functionalized with cysteine as a fluorescence sensor and Exploration of paper chip for p-nitrophenol detection

The large use and emission of p-nitrophenol (p-NP) seriously pollute the environment and endanger human health. In this work, a hydrazone-linked fluorescent covalent organic framework (BATHz-COF) was simply synthesized at room temperature and covalently linked N-acetyl-L-cysteine (NALC) via the "thiol-ene" click reaction, where carboxyl groups were introduced to improve dispersion and fluorescence intensity. As a rapid, good selectivity and reusability fluorescence sensor, the obtained COF-NALC has been used for quantitative analysis of p-NP predicated on the internal filtering effect (IFE). Under optimal conditions, COF-NALC enabled quantitative detection of p-NP with a linear range of 5-50 μM and the detection limit was 1.46 μM. The application of COF-NALC to the detection of p-NP in river water samples was successful, and the satisfactory recoveries were 98.0%-109.3%. Furthermore, the fluorescent COF paper chips constructed by in situ growth were combined with a smartphone to build a visual platform for the quick and real-time detection of p-NP, providing an excellent illustration for the development of intelligent fluorescence sensing in environmental analysis.

High-Performance Trimethylamine Sensor Based on an Imine Covalent Organic Framework

As trimethylamine (TMA) is widely used in agriculture and industry, inhalation of TMA can cause very serious negative effects on human health. However, most of the current gas sensors for detecting TMA are commonly performed at high temperatures and cannot meet market needs. Inspired by this, we prepared imine covalent organic frameworks (TB-COF) synthesized from two monomers, 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 1,3,5-benzotricarboxaldehyde (BTCA), using acetic acid as a catalyst at room temperature. Based on this, three sensors were prepared for gas sensitivity testing, namely, TA, BT, and TB-COF sensors. The three sensors were tested for 15 different gases at room temperature. From the whole gas sensitivity data, the TB-COF sensor made by compositing TA and BT has a higher sensitivity (6845.9%) to TMA at 500 ppm, which is 6.1 and 5.4 times higher than the response of TA and BT sensors, respectively. The TB-COF sensor adsorbs and desorbs TMA in a controlled 23 s cycle with a low detection limit of 28.6 ppb. This result indicates that TB-COF prepared at room temperature can be used as a gas-sensitive sensing material for real-time monitoring of TMA. The gas sensing results demonstrate the great potential of COFs for sensor development and application and provide ideas for further development of COFs-based gas sensors.

Integrating molecular imprinting into flexible covalent organic frameworks for selective recognition and efficient extraction of aflatoxins

Covalent organic frameworks (COFs) are promising adsorbents for extraction, but their selectivity for molecular recognition remains a challenging issue due to the very limited structural design with rigid structure. Herein, we report an elegant strategy for the design and synthesis of molecularly imprinted flexible COFs (MI-FCOFs) via one-pot reaction between the flexible building block of 2,4,6-tris(4-formylphenoxy)- 1,3,5-triazine and linear 4-phenylenediamine for selective extraction of aflatoxins. The flexible chain structure enabled the developed MI-FCOF to adjust the shape and conformation of frameworks to suit the template molecule, giving high selectivity for aflatoxins recognition. Moreover, MI-FCOF with abundant imprinted sites and function groups exhibited an exceptional adsorption capacity of 258.4 mg g-1 for dummy template which is 3 times that of no-imprinted FCOF (NI-FCOF). Coupling MI-FCOF based solid-phase extraction with high-performance liquid chromatography gave low detection limits of 0.003-0.09 ng mL-1 and good precision with relative standard deviations ≤ 6.7% for the determination of aflatoxins. Recoveries for the spiked rice, corn, wheat and peanut samples were in the range of 85.4%- 105.4%. The high selectivity of the developed MI-FCOF allows matrix-free determination of AFTs in food samples. This work offers a new way to the design of MI-FCOF for selective molecular recognition.

Two-dimensional nanomaterials induced nano-bio interfacial effects and biomedical applications in cancer treatment

Two-dimensional nanomaterials (2D NMs), characterized by a large number of atoms or molecules arranged in one dimension (typically thickness) while having tiny dimensions in the other two dimensions, have emerged as a pivotal class of materials with unique properties. Their flat and sheet-like structure imparts distinctive physical, chemical, and electronic attributes, which offers several advantages in biomedical applications, including enhanced surface area for efficient drug loading, surface-exposed atoms allowing precise chemical modifications, and the ability to form hierarchical multilayer structures for synergistic functionality. Exploring their nano-bio interfacial interactions with biological components holds significant importance in comprehensively and systematically guiding safe applications. However, the current lack of in-depth analysis and comprehensive understanding of interfacial effects on cancer treatment motivates our ongoing efforts in this field. This study provides a comprehensive survey of recent advances in utilizing 2D NMs for cancer treatment. It offers insights into the structural characteristics, synthesis methods, and surface modifications of diverse 2D NMs. The investigation further delves into the formation of nano-bio interfaces during their in vivo utilization. Notably, the study discusses a wide array of biomedical applications in cancer treatment. With their potential to revolutionize therapeutic strategies and outcomes, 2D NMs are poised at the forefront of cancer treatment, holding the promise of transformative advancements.

Recent progress in the synthesis and applications of covalent organic framework-based composites

Covalent organic frameworks (COFs) have historically been of interest to researchers in different areas due to their distinctive characteristics, including well-ordered pores, large specific surface area, and structural tunability. In the past few years, as COF synthesis techniques developed, COF-based composites fabricated by integrating COFs and other functional materials including various kinds of metal or metal oxide nanoparticles, ionic liquids, metal-organic frameworks, silica, polymers, enzymes and carbon nanomaterials have emerged as a novel kind of porous hybrid material. Herein, we first provide a thorough summary of advanced strategies for preparing COF-based composites; then, the emerging applications of COF-based composites in diverse fields due to their synergistic effects are systematically highlighted, including analytical chemistry (sensing, extraction, membrane separation, and chromatographic separation) and catalysis. Finally, the current challenges associated with future perspectives of COF-based composites are also briefly discussed to inspire the advancement of more COF-based composites with excellent properties.

Fouling-resistant electrode for electrochemical sensing based on covalent-organic frameworks TpPA-1 dispersed cabon nanotubes

The key problem that limits the practical applications of nonenzymatic electrochemical sensors in biological media, is the biofouling and chemical fouling of electrodes due to the adsorption of biological molecules and oxidation (reduction) products. Electrode fouling will cause low accuracy, poor stability, and low sensitivity. Here, a simple and efficient antifouling electrode was demonstrated for electrochemical sensing based on covalent-organic framework (COF) TpPA-1 and carboxylic multi-walled carbon nanotubes (CNT) composites. COF TpPA-1 possesses abundant hydrophilic groups, which assisted the dispersion of CNT in water and formed uniform composites by π-π interaction. In addition, the introduction of CNT into the composites improved the electron transfer rate of COF TpPA-1. The antifouling interface was characterized by electrochemistry, contact angle measurement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The electrode showed good chemical and bio-fouling resistant performance for the electrochemical detection of β-nicotinamide adenine dinucleotide (NADH) and uric acid (UA) in real serum samples.

Chemical Sensors Based on Covalent Organic Frameworks

Covalent organic frameworks (COFs) are a type of crystalline porous polymer composed of light elements through strong covalent bonds. COFs have attracted considerable attention due to their unique designable structures and excellent material properties. Currently, COFs have shown outstanding potential in various fields, including gas storage, pollutant removal, catalysis, adsorption, optoelectronics, and their research in the sensing field is also increasingly flourishing. In this review, we focus on COF-based sensors. Firstly, we elucidate the fundamental principles of COF-based sensors. Then, we present the primary application areas of COF-based sensors and their recent advancements, encompassing gas, ions, organic compounds, and biomolecules sensing. Finally, we discuss the future trends and challenges faced by COF-based sensors, outlining their promising prospects in the field of sensing.

Advances of Electrochemical and Electrochemiluminescent Sensors Based on Covalent Organic Frameworks

Covalent organic frameworks (COFs), a rapidly developing category of crystalline conjugated organic polymers, possess highly ordered structures, large specific surface areas, stable chemical properties, and tunable pore microenvironments. Since the first report of boroxine/boronate ester-linked COFs in 2005, COFs have rapidly gained popularity, showing important application prospects in various fields, such as sensing, catalysis, separation, and energy storage. Among them, COFs-based electrochemical (EC) sensors with upgraded analytical performance are arousing extensive interest. In this review, therefore, we summarize the basic properties and the general synthesis methods of COFs used in the field of electroanalytical chemistry, with special emphasis on their usages in the fabrication of chemical sensors, ions sensors, immunosensors, and aptasensors. Notably, the emerged COFs in the electrochemiluminescence (ECL) realm are thoroughly covered along with their preliminary applications. Additionally, final conclusions on state-of-the-art COFs are provided in terms of EC and ECL sensors, as well as challenges and prospects for extending and improving the research and applications of COFs in electroanalytical chemistry.

Simulation insights into the lipase adsorption on zeolitic imidazolate framework-8

Zeolitic imidazolate frameworks (ZIFs) have recently emerged as immobilization matrices for biomolecules, most notably enzymes. Understanding the key factors that dominate the enzyme's catalytic activity on/in ZIFs is crucial for the development of new immobilization matrices. In this work, a combination of the parallel tempering Monte Carlo simulation and all-atom molecular dynamics simulation is performed to study the orientation and conformation of the Candida rugose lipase (CRL) adsorbed on oppositely charged and neutral ZIF-8 (i.e., ZIF-8-COOH, ZIF-8-NH2, and ZIF-8-neutral) surfaces. The results show that CRL could adsorb on all ZIF-8 surfaces, with an ordered orientation obtained on charged ZIF-8 surfaces. ZIF-8-NH2 is a good candidate for CRL immobilization since it can maximize the catalytic activity of CRL. The native conformation of CRL is well preserved on all three surfaces due to the partially water-containing surface of ZIF-8. The results could provide theoretical support for the application of porous materials in enzyme immobilization.

Strategies to control mycotoxins and toxigenic fungi contamination by nano-semiconductor in food and agro-food: a review

Mycotoxins are toxic secondary metabolites generated from toxigenic fungi in the contaminated food and agro-food, which have been regarded as a serious threat to the food safety and human health. Therefore, the control of mycotoxins and toxigenic fungi contamination is of great significance and has attracted the increasing attention of researchers. As we know, nano-semiconductors have many unique properties such as large surface area, structural stability, good biocompatibility, excellent photoelectrical properties, and low cost, which have been developed and applied in many research fields. Recently, nano-semiconductors have also been promisingly applied in mitigating or controlling mycotoxins and toxigenic fungi contaminations in food and agro-food. In this review, the type, occurrence, and toxicity of main mycotoxins in food and agro-food were introduced. Then, a variety of strategies to mitigate the mycotoxin contamination based on nano-semiconductors involving mycotoxins detection, inhibition of toxigenic fungi, and mycotoxins degradation were summarized. Finally, the outlook, opportunities, and challenges have prospected in the future for the mitigation of mycotoxins and toxigenic fungi based on nano-semiconductors.

Drug delivery using biocompatible covalent organic frameworks (COFs) towards a therapeutic approach

Covalent organic frameworks (COFs) are constructed exclusively with lightweight organic scaffolds, which can have a 2D or 3D architecture. The ease of synthesis, robust skeleton and tunable properties of COFs make them superior candidates among their counterparts for a wide range of uses including biomedical applications. In the biomedical field, drug delivery or photodynamic-photothermal (PDT-PTT) therapy can be individually considered a potential parameter to be investigated. Therefore, this comprehensive review is focused on drug delivery using COFs, highlighting the encapsulation and decapsulation of drugs by COF scaffolds and their delivery in biological media including live cells. Versatile COF scaffolds together with the delivery of several drug molecules are considered. We attempted to incorporate the status of drug encapsulation and decapsulation considering a wide range of recent publications.

Post-synthetic modifications of covalent organic frameworks (COFs) for diverse applications

Covalent organic frameworks (COFs) are porous and crystalline organic polymers, which have found usage in various fields. These frameworks are tailorable through the introduction of diverse functionalities into the platform. Indeed, functionality plays a key role in their different applications. However, sometimes functional groups are not compatible with reaction conditions or can compete and interfere with other groups of monomers in the direct synthetic method. Also, pre-synthesis of bulky moieties in COFs can negatively affect crystal formation. To avoid these problems a post-synthetic modification (PSM) approach is a helpful tactic. Also, with the assistance of this strategy porous size can be tunable and stability can be improved without considerable effect on the crystallite. In addition, conductivity, hydrophobicity/ hydrophilicity, and chirality are among the features that can be reformed with this method. In this review, different types of PSM strategies based on recent articles have been divided into four categories: (i) post-functionalization, (ii) post-metalation, (iii) chemical locking, and (iv) host-guest post-modifications. Post-functionalization and chemical locking methods are based on covalent bond formation while in post-metalation and host-guest post-modifications, non-covalent bonds are formed. Also, the potential of these post-modified COFs in energy storage and conversion (lithium-sulfur batteries, hydrogen storage, proton-exchange membrane fuel cells, and water splitting), heterogeneous catalysts, food safety evaluation, gas separation, environmental domains (greenhouse gas capture, radioactive element uptake, and water remediation), and biological applications (drug delivery, biosensors, biomarker capture, chiral column chromatography, and solid-state smart nanochannels) have been discussed.

Triazine-based covalent-organic framework embedded with cuprous oxide as the bioplatform for photoelectrochemical aptasensing Escherichia coli

A superior photoelectrochemical (PEC) aptasensor was manufactured for the detection of Escherichia coli (E. coli) based on a hybrid of triazine-based covalent-organic framework (COF) and cuprous oxide (Cu2O). The COF synthesized using 1,3,5-tris(4-aminophenyl)-benzene (TAPB) and 1,3,5-triformylphloroglucinol (Tp) as building blocks acted as a scaffold for encapsulated Cu2O nanoparticles (denoted as Cu2O@TAPB-Tp-COF), which then was employed as the bioplatform for anchoring E. coli-targeted aptamer. Cu2O@Cu@TAPB-Tp-COF demonstrated enhanced separation of the photogenerated carriers and photoabsorption ability and boosted photoelectric conversion efficiency. The developed Cu2O@TAPB-Tp-COF-based PEC aptasensor exhibited a lower detection limit of 2.5 CFU mL-1 toward E. coli within a wider range of 10 CFU mL-1 to 1 × 104 CFU mL-1 than most of reported aptasensors for determining foodborne bacteria, together with high selectivity, good stability, and superior ability and reproducibility. The recoveries of E. coli spiked into milk and bread samples ranged within 95.3-103.6% and 96.6-102.8%, accompanying with low RSDs of 1.37-4.48% and 1.74-3.66%, respectively. The present study shows a promising alternative for the sensitive detection of foodborne bacteria from complex foodstuffs and pathogenic bacteria-polluted environment.

Improving the Bioactivity and Stability of Embedded Enzymes by Covalent Organic Frameworks

De novo embedding enzymes within reticular chemistry materials have shown the enhancement of physical and chemical stability for versatile catalytic reactions. Compared to metal-organic frameworks (MOFs), covalent organic frameworks (COFs) are usually considered to be the more superior host of enzymes because of their large channels with low diffusion barriers, outstanding chemical/thermal stability, and metal-free nature. However, detailed investigations on the comparison of COFs and MOFs in enhancing biocatalytic performance have not been explored. Here, we de novo encapsulated enzymes within two COFs via a mechanochemical strategy, which avoided the extreme synthetic conditions of COFs and highly maintained the biological activities of the embedded enzymes. The enzymes@COFs biocomposites exhibited a much higher activity (3.4-14.7 times higher) and enhanced stability than those in MOFs (ZIF-8, ZIF-67, HKUST-1, MIL-53, and CaBDC), and the rate parameter (kcat/Km) of enzyme@COFs was 41.3 times higher than that of enzyme@ZIF-8. Further explorations showed that the conformation of enzymes inside MOFs was disrupted, owing to the harmful interfacial interactions between enzymes and metal ions as confirmed by ATR-FTIR, fluorescence spectroscopy, and XPS data. In contrast, enzymes that were embedded in metal-free COFs highly preserved the natural conformation of free enzymes. This study provides a better understanding of the interfacial interactions between reticular supports and enzymes, which paves a new road for optimizing the bioactivities of immobilized enzymes.

Review of covalent organic frameworks for enzyme immobilization: Strategies, applications, and prospects

Efficient enzyme immobilization systems offer a promising approach for improving enzyme stability and recyclability, reducing enzyme contamination in products, and expanding the applications of enzymes in the biomedical field. Covalent organic frameworks (COFs) possess high surface areas, ordered channels, optional building blocks, highly tunable porosity, stable mechanical properties, and abundant functional groups, making them ideal candidates for enzyme immobilization. Various COF-enzyme composites have been successfully synthesized, with performances that surpass those of free enzymes in numerous ways. This review aims to provide an overview of current enzyme immobilization strategies using COFs, highlighting the characteristics of each method and recent research applications. The future opportunities and challenges of enzyme immobilization technology using COFs are also discussed.

Lanthanide Functionalized Covalent Organic Frameworks Hybrid Materials for Luminescence Responsive Chemical Sensing

Covalent organic frameworks (COFs) possess several unique features of structural and functional chemistry, together with other modular photophysical performance, which make them candidates for luminescence responsive chemical sensing. Lanthanide (Ln3+ ) functionalized COFs hybrid materials still keep the parent COFs' virtues and also embody the abundant multiple luminescence response with both COFs and Ln3+ ions or other guest species. In this review, the summary is highlighted on the lanthanide functionalized COFs hybrid materials and their relevant systems for luminescence responsive chemical sensing. It is subdivided into five sections involving the three main topics. Firstly, the basic knowledges of COFs materials related to the luminescence responsive chemical sensing are introduced (including three sections), involving the chemistry, application and post-synthetic modification (PSM) of COFs, the luminescence and luminescence responsive chemical sensing, and the luminescence responsive chemical sensing of non-lanthanide functionalized COFs hybrids materials. Secondly, the systematic progresses are outlined on the lanthanide functionalized COFs hybrid materials in luminescence responsive chemical sensing, which is the emphasis for this review. Finally, the conclusion and prospect are given.

Building Blocks and COFs Formed in Concert-Three-Component Synthesis of Pyrene-Fused Azaacene Covalent Organic Framework in the Bulk and as Films

A three-component synthesis methodology is described for the formation of covalent organic frameworks (COFs) containing extended aromatics. Notably, this approach enables synthesis of the building blocks and COF along parallel reaction landscapes, on a similar timeframe. The use of fragmental building block components, namely pyrene dione diboronic acid as aggregation-inducing COF precursor and the diamines o-phenylenediamine (Ph), 2,3-diaminonaphthalene (Naph), or (1R,2R)-(+)-1,2-diphenylethylenediamine (2Ph) as extending functionalization units in conjunction with 2,3,6,7,10,11-hexahydroxytriphenylene, resulted in the formation of the corresponding pyrene-fused azaacene, i.e., Aza-COF series with full conversion of the dione moiety, long-range order, and high surface area. In addition, the novel three-component synthesis was successfully applied to produce highly crystalline, oriented thin films of the Aza-COFs with nanostructured surfaces on various substrates. The Aza-COFs exhibit light absorption maxima in the blue spectral region, and each Aza-COF presents a distinct photoluminescence profile. Transient absorption measurements of Aza-Ph- and Aza-Naph-COFs suggest ultrafast relaxation dynamics of excited-states within these COFs.

Covalent organic frameworks assisted for food safety analysis

Food safety incidents threaten human health and life safety. It is an effective method to prevent and control the occurrence of food safety events by enhancing the rapid and sensitive detection of food contaminants. Emerging porous materials provide for the development of efficient and stable detection methods. Covalent organic frameworks (COFs) are favored by researchers for their highly ordered pore structure, large specific surface area, and good structural and functional designability. Especially in the sensing field, COFs play the roles of carriers, conductors, quenchers, and reporters, and have broad application prospects. To better understand COFs-based sensing studies, this review briefly introduces the characteristics and different functional roles of COFs in food safety analysis, focusing on the applications of COFs in the detection of various food contaminants (including foodborne pathogens, mycotoxins, pesticides, antibiotics, heavy metals, and others). Finally, the challenges and opportunities for COFs-based sensing are discussed to facilitate further applications and development of COFs in food safety.

Composite materials based on covalent organic frameworks for multiple advanced applications

Covalent organic frameworks (COFs) stand for a class of emerging crystalline porous organic materials, which are ingeniously constructed with organic units through strong covalent bonds. Their excellent design capabilities, and uniform and tunable pore structure make them potential materials for various applications. With the continuous development of synthesis technique and nanoscience, COFs have been successfully combined with a variety of functional materials to form COFs-based composites with superior performance than individual components. This paper offers an overview of the development of different types of COFs-based composites reported so far, with particular focus on the applications of COFs-based composites. Moreover, the challenges and future development prospects of COFs-based composites are presented. We anticipate that the review will provide some inspiration for the further development of COFs-based composites.

Highly efficient nanocomposites based on molecularly imprinted magnetic covalent organic frameworks for selective extraction of bisphenol A from liquid matrices

Highly efficient nanocomposites, hydrophobic molecularly imprinted magnetic covalent organic frameworks (MI-MCOF), have been farbricated by a facile Schiff-base reaction. The MI-MCOF was based on terephthalaldehyde (TPA) and 1,3,5-tris(4-aminophenyl) benzene (TAPB) as functional monomer and crosslinker, anhydrous acetic acid as catalyst, bisphenol AF as dummy template, and NiFe₂O₄ as magnetic core. This organic framework significantly reduced the time consumption of conventional imprinted polymerization and avoided the use of traditional initiator and cross-linking agents. The synthesized MI-MCOF exhibited superior magnetic responsivity and affinity, as well as high selectivity and kinetics for bisphenol A (BPA) in water and urine samples. The equilibrium adsorption capacity (Q_e) of BPA on the MI-MCOF was 50.65 mg g^-1, which was 3-7-fold higher than of its three structural analogues. The imprinting factor of BPA reached up to 3.17, and the selective coefficients of three analogues were all > 2.0, evidencing the excellent selectivity of fabricated nanocomposites to BPA. Based on the MI-MCOF nanocomposites, the magnetic solid-phase extraction (MSPE), combined with HPLC and fluorescence detection (HPLC-FLD), offered superior analytical performance: wide linear range of 0.1-100 μg L^-1, high correlation coefficient of 0.9996, low limit of detection of 0.020 μg L^-1, good recoveries of 83.5-110%, and relative standard deviations (RSDs) of 0.5-5.7% in environmental water, beverage, and human urine samples. Consequently, the MI-MCOF-MSPE/HPLC-FLD method provides a good prospect in selective extraction of BPA from complex matrices while replacing traditional magnetic separation and adsorption materials.

An in-situ strategy to construct uracil-conjugated covalent organic frameworks with tunable fluorescence/recognition characteristics for sensitive and selective Mercury(II) detection

Previous researches of covalent organic frameworks (COFs) have shown their potential as fluorescent probes, but the regulation of their optical properties and recognition characteristics still remains a challenge, and most of reports required complicated post-decoration to improve the sensing performance. In this context, we propose a novel in-situ strategy to construct uracil-conjugated COFs and modulate their fluorescence properties for sensitive and selective mercury(II) detection. By using 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) and 1,3,6,8-tetrakis(4-aminophenyl)pyrene (TAPPy) as fundamental blocks and 5-aminouraci (5-AU) as the functional monomer, a series of COFs (Py-COFs and Py-U-COFs-1 to Py-U-COFs-5) with tunable fluorescence were solvothermally synthesized through an in-situ Schiff base reaction. The π-conjugated framework serves as a signal reporter, the evenly and densely distributed uracil acts as a mercury(II) receptor, and the regular pores (channels) make the rapid and sensitive detection of the mercury(II) possible. In this research, we manage to regulate the crystalline structure, the fluorescence properties, and the sensing performance of COFs by simply changing the molar ratio of precursors. We expect this research to open up a new strategy for effective and controllable construction of functionalized COFs for environmental analysis.

Covalent organic framework: A state-of-the-art review of electrochemical sensing applications

Covalent organic framework (COF), a kind of porous polymer with crystalline properties, is a periodic porous framework material with precise regulation at atomic level, which can be formed by the orderly connection of pre-designed organic construction units through covalent bonds. Compared with metal-organic frameworks, COFs exhibit unique performance, including tailor-made functions, stronger load ability, structural diversity, ordered porosity, intrinsic stability and excellent adsorption features, are more conducive to the expansion of electrochemical sensing applications and the universality of applications. In addition, COFs can accurately integrate organic structural units with atomic precision into ordered structures, so that the structural diversity and application of COFs can be greatly enriched by designing new construction units and adopting reasonable functional strategies. In this review, we mainly summarized state-of-the-art recent advances of the classification and synthesis strategy of COFs, the design of functionalized COF for electrochemical sensors and COFs-based electrochemical sensing. Then, an overview of the considerable recent advances made in applying outstanding COFs to establish electrochemical sensing platform, including electrochemical sensor based on voltammetry, amperometry, electrochemical impedance spectroscopy, electrochemiluminescence, photoelectrochemical sensor and others. Finally, we discussed the positive outlooks, critical challenges and bright directions of COFs-based electrochemical sensing in the field of disease diagnosis, environmental monitoring, food safety, drug analysis, etc.

Engineering Single-Atom Nanozymes for Catalytic Biomedical Applications

Nanomaterials with enzyme-mimicking properties, coined as nanozymes, are a promising alternative to natural enzymes owing to their remarkable advantages, such as high stability, easy preparation, and favorable catalytic performance. Recently, with the rapid development of nanotechnology and characterization techniques, single atom nanozymes (SAzymes) with atomically dispersed active sites, well-defined electronic and geometric structures, tunable coordination environment, and maximum metal atom utilization are developed and exploited. With superior catalytic performance and selectivity, SAzymes have made impressive progress in biomedical applications and are expected to bridge the gap between artificial nanozymes and natural enzymes. Herein, the recent advances in SAzyme preparation methods, catalytic mechanisms, and biomedical applications are systematically summarized. Their biomedical applications in cancer therapy, oxidative stress cytoprotection, antibacterial therapy, and biosensing are discussed in depth. Furthermore, to appreciate these advances, the main challenges, and prospects for the future development of SAzymes are also outlined and highlighted in this review.

Covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) as electrochemical sensors for the efficient detection of pharmaceutical residues

Pharmaceutical residues are the undecomposed remains from drugs used in the medical and food industries. Due to their potential adverse effects on human health and natural ecosystems, they are of increasing worldwide concern. The acute detection of pharmaceutical residues can give a rapid examination of their quantity and then prevent them from further contamination. Herein, this study summarizes and discusses the most recent porous covalent-organic frameworks (COFs) and metal-organic frameworks (MOFs) for the electrochemical detection of various pharmaceutical residues. The review first introduces a brief overview of drug toxicity and its effects on living organisms. Subsequently, different porous materials and drug detection techniques are discussed with materials' properties and applications. Then the development of COFs and MOFs has been addressed with their structural properties and sensing applications. Further, the stability, reusability, and sustainability of MOFs/COFs are reviewed and discussed. Besides, COFs and MOFs' detection limits, linear ranges, the role of functionalities, and immobilized nanoparticles are analyzed and discussed. Lastly, this review summarized and discussed the MOF@COF composite as sensors, the fabrication strategies to enhance detection potential, and the current challenges in this area.

Covalent Organic Frameworks-Based Electrochemical Sensors for Food Safety Analysis

Food safety is a key issue in promoting human health and sustaining life. Food analysis is essential to prevent food components or contaminants causing foodborne-related illnesses to consumers. Electrochemical sensors have become a desirable method for food safety analysis due to their simple, accurate and rapid response. The low sensitivity and poor selectivity of electrochemical sensors working in complex food sample matrices can be overcome by coupling them with covalent organic frameworks (COFs). COFs are a kind of novel porous organic polymer formed by light elements, such as C, H, N and B, via covalent bonds. This review focuses on the recent progress in COF-based electrochemical sensors for food safety analysis. Firstly, the synthesis methods of COFs are summarized. Then, a discussion of the strategies is given to improve the electrochemistry performance of COFs. There follows a summary of the recently developed COF-based electrochemical sensors for the determination of food contaminants, including bisphenols, antibiotics, pesticides, heavy metal ions, fungal toxin and bacterium. Finally, the challenges and the future directions in this field are discussed.

Facile synthesis of hollow microtubular COF as enrichment probe for quantitative detection of ultratrace quinones in mice plasma with APGC-MS/MS

A hollow microtubular covalent organic framework (denoted as TatDha-COF) was synthesized by solvothermal method for the enrichment and determination of quinones. The TatDha-COF showed large specific surface area (2057 m² g^-1), good crystal structure, ordered pore size distribution (2.3 nm), stable chemical properties and good reusability. Accordingly, a simple and efficient method based on dispersive solid-phase extraction (d-SPE) and atmospheric pressure gas chromatography tandem mass spectrometry (APGC-MS/MS) was developed for the determination of quinones in complex samples. The established method demonstrated a wide liner range, good linearity (r>0.9990), high enrichment factors (EFs, 24-69-folds) and low detection limits (LODs, 0.200-30.0 pg L^-1, S/N≥3). On this basis, the suggested method was successfully applied to sensitively detect the eight ultratrace quinones in mice plasma. Overall, the established method has provided a powerful tool for the enrichment and detection of ultratrace quinones in complex samples, presenting the promising application of TatDha-COF in sample pretreatment.

Highly Crystalline Polyimide Covalent Organic Framework as Dual-Active-Center Cathode for High-Performance Lithium-Ion Batteries

Polyimide covalent organic framework (PI-COF) materials that can realize intrinsic redox reactions by changing the charge state of their electroactive sites are considered as emerging electrode materials for rechargeable devices. However, the highly crystalline PI-COFs with hierarchical porosity are less reported due to the rapid reaction between monomers and the poor reversibility of the polyimidization reaction. Here, we developed a water-assistant synthetic strategy to adjust the reaction rate of polyimidization, and PI-COF (COF_TPDA-PMDA) with kgm topology consisting of dual active centers of N,N,N',N'-tetrakis(4-aminophenyl)-1,4-benzenediamine (TPDA) and pyromellitic dianhydride (PMDA) ligands was successfully synthesized with high crystallinity and porosity. The COF_TPDA-PMDA possesses hierarchical micro-/mesoporous channels with the largest surface area (2669 m²/g) in PI-COFs, which can promote the Li⁺ ions and bulky bis(trifluoromethanesulfonyl)imide (TFSI^-) ions in organic electrolyte to sufficiently interact with the dual active sites on COF skeleton to increase the specific capacity of cathode materials. As a cathode material for lithium-ion batteries, COF_TPDA-PMDA@50%CNT which integrated high surface area and dual active center of COF_TPDA-PMDA with carbon nanotubes via π-π interactions gave a high initial charge capacity of 233 mAh/g (0.5 A/g) and maintains at 80 mAh/g even at a high current density of 5.0 A/g after 1800 cycles.

Point-of-care CRISPR/Cas biosensing technology: A promising tool for preventing the possible COVID-19 resurgence caused by contaminated cold-chain food and packaging

The ongoing coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused great public health concern and has been a global threat due to its high transmissibility and morbidity. Although the SARS-CoV-2 transmission mainly relies on the person-to-person route through the respiratory droplets, the possible transmission through the contaminated cold-chain food and packaging to humans has raised widespread concerns. This review discussed the possibility of SARS-CoV-2 transmission via the contaminated cold-chain food and packaging by tracing the occurrence, the survival of SARS-CoV-2 in the contaminated cold-chain food and packaging, as well as the transmission and outbreaks related to the contaminated cold-chain food and packaging. Rapid, accurate, and reliable diagnostics of SARS-CoV-2 is of great importance for preventing and controlling the COVID-19 resurgence. Therefore, we summarized the recent advances on the emerging clustered regularly interspaced short palindromic repeats (CRISPR)/Cas system-based biosensing technology that is promising and powerful for preventing the possible COVID-19 resurgence caused by the contaminated cold-chain food and packaging during the COVID-19 pandemic, including CRISPR/Cas system-based biosensors and their integration with portable devices (e.g., smartphone, lateral flow assays, microfluidic chips, and nanopores). Impressively, this review not only provided an insight on the possibility of SARS-CoV-2 transmission through the food supply chain, but also proposed the future opportunities and challenges on the development of CRISPR/Cas system-based detection methods for the diagnosis of SARS-CoV-2.

CRISPR/Cas Systems-Inspired Nano/Biosensors for Detecting Infectious Viruses and Pathogenic Bacteria

Infectious pathogens cause severe human illnesses and great deaths per year worldwide. Rapid, sensitive, and accurate detection of pathogens is of great importance for preventing infectious diseases caused by pathogens and optimizing medical healthcare systems. Inspired by a microbial defense system (i.e., CRISPR/ CRISPR-associated proteins (Cas) system, an adaptive immune system for protecting microorganisms from being attacked by invading species), a great many new biosensors have been successfully developed and widely applied in the detection of infectious viruses and pathogenic bacteria. Moreover, advanced nanotechnologies have also been integrated into these biosensors to improve their detection stability, sensitivity, and accuracy. In this review, the recent advance in CRISPR/Cas systems-based nano/biosensors and their applications in the detection of infectious viruses and pathogenic bacteria are comprehensively reviewed. First of all, the categories and working principles of CRISPR/Cas systems for establishing the nano/biosensors are simply introduced. Then, the design and construction of CRISPR/Cas systems-based nano/biosensors are comprehensively discussed. In the end, attentions are focused on the applications of CRISPR/Cas systems-based nano/biosensors in the detection of infectious viruses and pathogenic bacteria. Impressively, the remaining opportunities and challenges for the further design and development of CRISPR/Cas system-based nano/biosensors and their promising applications are proposed.

Facile synthesis of surface functionalized Pd2+@P-CDP/COFs for highly sensitive detection of norfloxacin drug based on the host-guest interaction

In this work, β-cyclodextrin porous polymers (P-CDPs) functionalized novel covalent organic frameworks (P-CDPs/COFs) were synthesized by a simple and facile method. After combined with Pd²⁺ via electrostatic interaction, the Pd²⁺@P-CDPs/COFs nanocomposites were prepared and utilized as novel electrode materials to fabricate the non-enzyme electrochemical sensors for high-sensitivity detection of Norfloxacin (NF). Due to the host-guest recognition, excellent adsorption performance and catalytic performance of Pd²⁺@P-CDPs/COFs, the prepared sensor exhibited excellent electrochemical performance for detecting NF under the optimum conditions, which showed two linear ranges of 0.08-7.0 μM and 7.0-100.0 μM with a low detection limit of 0.031 μM (S/N = 3). Additionally, the obtained sensor has also been successfully applied to measure NF with satisfactory results in the real medicinal samples of NF eye-drops. Our findings paved the way for the development of COFs-based sensing platform in drug analysis and testing for human health, food security and the quality control of drugs.

Metalated covalent organic frameworks: from synthetic strategies to diverse applications

Covalent organic frameworks (COFs) are a class of organic crystalline porous materials discovered in the early 21st century that have become an attractive class of emerging materials due to their high crystallinity, intrinsic porosity, structural regularity, diverse functionality, design flexibility, and outstanding stability. However, many chemical and physical properties strongly depend on the presence of metal ions in materials for advanced applications, but metal-free COFs do not have these properties and are therefore excluded from such applications. Metalated COFs formed by combining COFs with metal ions, while retaining the advantages of COFs, have additional intriguing properties and applications, and have attracted considerable attention over the past decade. This review presents all aspects of metalated COFs, from synthetic strategies to various applications, in the hope of promoting the continued development of this young field.

Facile Preparation of a Thienoisoindigo-Based Nanoscale Covalent Organic Framework with Robust Photothermal Activity for Cancer Therapy

The covalent organic frameworks (COFs) so far are usually built with small aromatic subunits, which makes their absorption spectra mainly located in the high-energy part of the visible region. In this work, we have developed a COF with a low band gap by integrating electron-deficient thienoisoindigo and electron-rich triphenylamine. The intramolecular charge-transfer effect combining the extended length of the π-conjugated backbone of COF endow it with broad absorption even to the second near-infrared region. After optimizing the solvent, a uniform size and colloidal stable COF is obtained. Benefiting from the coplanar structure of the monomer, this COF achieves a considerable photothermal conversion efficiency (PCE) of 48.2%. With these advantages, it displays convincing cancer cell killing effect upon laser irradiation in vitro or in vivo. This work provides a simple and practical method to acquire promising a COF-based phototherapy reagent that is applied in biomedicine field.

COF-43 based voltammetric sensor for Ag(I) determination: optimization of experimental conditions by Box-Behnken design

Hydrazone-linked covalent organic framework-43 (COF-43) was synthesized and the carbon paste electrode (CPE) modified with this COF was used as a voltammetric sensor to measure silver(I). Various characterization tests (XRD, FTIR, BET, SEM/EDX, electrochemical impedance (EIS), and cyclic voltammetry (CV)) were performed on the synthesized COF-43 and the prepared COF-43/CPE. Box-Behnken design was used to optimize the preparation and operation conditions of the sensor. EIS and CV investigations reveal the diffusive characteristics of silver transport in the electrode matrix. An appropriate mechanism for the sensor procedure has been suggested and ratified by electrochemical and SEM/EDX techniques. The COF-43 used has several recognition elements for the selective binding of silver ion and due to its high porosity provides a large space for the deposition and reduction of large amounts of silver. Therefore, due to the correct selection of COF used in the construction of the sensor, high selectivity and sensitivity for the prepared sensor has been achieved. The obtained data disclosed that the modification of the carbon paste electrode by COF-43 significantly improves the analytical characteristics of the sensor, which specifies the performance of COF-43 as a sensory material for determining silver(I). The obtained calibration curve is linear in the concentration range from 0.001 μM to 10.0 μM and the detection limit is 1.5 × 10^-10 M. Various statistical tests have been employed to evaluate the sensor performance. The appropriate accuracy and precision of the proposed method were confirmed using the analysis of variance (ANOVA) approach. Potential interferences were investigated and it was found that the other species did not have a significant effect on the sensor performance. The prepared sensor has been successfully used to measure silver in two samples of photographic effluents, bleaching, and fixing agents. The results from the analysis of real samples demonstrate the reliable applicability of the fabricated sensor.

Engineering single-atom catalysts toward biomedical applications

Due to inherent structural defects, common nanocatalysts always display limited catalytic activity and selectivity, making it practically difficult for them to replace natural enzymes in a broad scope of biologically important applications. By decreasing the size of the nanocatalysts, their catalytic activity and selectivity will be substantially improved. Guided by this concept, the advances of nanocatalysts now enter an era of atomic-level precise control. Single-atom catalysts (denoted as SACs), characterized by atomically dispersed active sites, strikingly show utmost atomic utilization, precisely located metal centers, unique metal-support interactions and identical coordination environments. Such advantages of SACs drastically boost the specific activity per metal atom, and thus provide great potential for achieving superior catalytic activity and selectivity to functionally mimic or even outperform natural enzymes of interest. Although the size of the catalysts does matter, it is not clear whether the guideline of "the smaller, the better" is still correct for developing catalysts at the single-atom scale. Thus, it is clearly a new, urgent issue to address before further extending SACs into biomedical applications, representing an important branch of nanomedicine. This review begins by providing an overview of recent advances of synthesis strategies of SACs, which serve as a basis for the discussion of emerging achievements in improving the enzyme-like catalytic properties at an atomic level. Then, we carefully compare the structures and functions of catalysts at various scales from nanoparticles, nanoclusters, and few-atom clusters to single atoms. Contrary to conventional wisdom, SACs are not the most catalytically active catalysts in specific reactions, especially those requiring multi-site auxiliary activities. After that, we highlight the unique roles of SACs toward biomedical applications. To appreciate these advances, the challenges and prospects in rapidly growing studies of SACs-related catalytic nanomedicine are also discussed in this review.