Size-Controllable Synthesis of Uniform Spherical Covalent Organic Frameworks at Room Temperature for Highly Efficient and Selective Enrichment of Hydrophobic Peptides

Covalent Organic Frameworks as Efficient Photoinitiators and Cross-Linkers To Fabricate Highly Stretchable Hydrogels

In this work, two kinds of imine-type covalent organic framework (COF) nanoparticles are demonstrated as efficient photocatalytic initiators to trigger the free-radical polymerization of acrylamide (AM) to prepare polyacrylamide (PAM) hydrogels under visible light irradiation, without any assistance from the co-initiator. Simultaneously, the COF nanoparticles bearing vinyl side groups (COF-V) promote covalent cross-linking of the polymer chains, which significantly reinforces the mechanical properties of the nanocomposite hydrogel. The obtained PAM/COF-V hydrogel is highly stretchable with an extraordinary elongation up to 3300% strain. On the other hand, the COF nanoparticles modified with methoxy moieties (COF-OMe) endow the resulting PAM/COF-OMe hydrogel with a promising fluorescence feature. In addition, this strategy provides a visible-light-regulated photocatalytic polymerization approach with a simplified recipe to fabricate COF-based nanocomposite hydrogels or resins with diverse functions.

Etching Bulk Covalent Organic Frameworks into Nanoparticles of Uniform and Controllable Size by the Molecular Exchange Etching Method for Sonodynamic and Immune Combination Antitumor Therapy

To improve the therapeutic effect of sonodynamic therapy (SDT), more effective and stable sonosensitizers and therapeutic strategies are still required. A covalent organic framework (COF) sonosensitizer is developed by using a new nanoscale COF preparation strategy. This strategy uses molecular etching based on the imine exchange reaction to etch the bulk COF into nanoparticles and has universal applicability to imine-bond-based COF. The regular COF structure can prevent the loss of sonodynamic performance caused by the aggregation of porphyrin molecules and improve the chemical stability of the porphyrin unit. In addition, the coordination of Fe³⁺ to COF endows the nanoparticle with chemodynamic therapy performance and glutathione consumption ability. The combination of enhanced SDT and α-PD-L1 antibody achieves a good antitumor effect. The innovative nanoscale COF sonosensitizer preparation strategy provides a new avenue for clinical antitumor therapy.

Highly selective adsorption of rare earth elements by honeycomb-shaped covalent organic frameworks synthesized in deep eutectic solvents

One of the key factors to obtain a highly pure individual rare earth element (REE) is to prepare adsorbents with high selectivity and adsorption capacity. Covalent organic frameworks (COFs), which encompass a variety of properties, including regular/tunable pore size, high specific surface area and easy functionalization, could be effective as adsorbents for separating rare earth elements (REEs). In this paper, TpPa COFs were successfully synthesized using an eco-friendly deep eutectic solvent (DES) as the reaction medium instead of toxic organic solvents at room temperature. TpPa COFs have a good separation effect on the nine REEs investigated in this work. Among them, the separation factors (β) of Eu/Yb, Eu/Tm and Eu/La are 15.34, 14.70 and 10.78, respectively, indicating that the TpPa COFs have good separation performance. Further discoveries showed that the adsorption and separation mechanism of the TpPa COFs for REEs in this experiment may be due to the coordination of REE ions with O to form a stable structure. This study blazed a trial for a green and facile synthesis strategy of TpPa COFs and expanded its implementation as a solid adsorbent in the separation of REEs.

Functionalization of Covalent Organic Frameworks with Peptides by Polymer-Assisted Surface Modification and the Application for Protein Detection

Although covalent organic frameworks (COFs) have received extensive attention for biomedical research due to their unique properties, their application is still hindered by the challenges of incorporating COFs with functional biomolecules. Since peptides have shown advantages in biomedical applications, herein, we propose the functionalization of COFs with peptides by a polymer-assisted surface modification strategy. Furthermore, a method based on the peptide-functionalized COFs for protein detection has also been developed to demonstrate their application potential. With the help of the polymers, peptides and horseradish peroxidase are attached onto COFs with a high surface density, and the developed method has achieved simple and sensitive detection of the secreted protein acidic and rich in cysteine. We speculate that the facile method proposed in this work to prepare peptide-functionalized COFs can not only benefit protein detection but also promote more biomedical applications of COFs.

Hydroxyl-riched covalent organic framework for solid-phase microextraction of flavonoids aglycones or their metabolites in mice's plasma: Luteolin and quercetagetin as examples

Herein, a hydroxyl‑riched covalent organic framework (named COF-DES-1) was synthesized using 1,3,5-tris(4-aminophenyl)benzene and 2,5-dihydroxyterephthalaldehyde as building blocks and employed as a coating of solid-phase microextraction (SPME) fiber. Ascribed to the advantages (e.g. suitable pore size and rich functional group characteristics) of coating, the SPME fiber showed good adsorption capacities to flavonoids aglycones including luteolin and quercetagetin, and the maximum adsorption capacities for them were 145.31 µg and 84.75 µg, respectively. Due to the size exclusion property of COF-DES-1, SPME fiber showed good protein exclusion effects on seven selected proteins with high exclusion efficiencies (>93%). Accordingly, an attractive strategy of the combination of COF-DES-1 based SPME fiber and HPLC-MS/MS was proposed for the extraction and determination of luteolin, quercetagetin or their metabolites. The results revealed that the fiber can be effectively applied to extract luteolin and its metabolites, and quercetagetin from mice's palsma. Compared with the traditional protein precipitation methods, the extraction effects of SPME fiber based extraction method were much better, indicating the promising applicability of the fiber for the enrichment of flavonoids aglycones or their metabolites in biological samples.

Fluorine-Functionalized Covalent-Organic-Framework-Coated Stir Bar for the Extraction of Benzoylurea Insecticides in Pear Juice and Beverage Followed by High-Performance Liquid Chromatography-Ultraviolet Detection

A fluorinated covalent organic framework (COF), named F-COF, was fabricated via simple room-temperature synthesis. With the characteristics of rich fluorine atoms, hydrophobicity, and large conjugated structure, F-COF was evaluated for the extraction of five benzoylurea insecticides (BUs) containing fluorine atoms, benzene ring, and urea bridge. Specifically, F-COF-coated stir bars were prepared by physical adhesion and exhibited higher extraction recovery (73-93 versus 40-85%) toward BUs than commercial stir bars in a shorter extraction time (50 min versus 24 h). The adsorption behavior of BUs on F-COF was explored, and it was assumed that the halogen bond (O-F), hydrophobic interaction, electrostatic interaction, and π-π stacking contributed to the adsorption. On the basis of it, a method combining stir bar sorptive extraction with liquid chromatography-ultraviolet detector was developed for trace analysis of five BUs. Under the optimal conditions, the limits of detection for BUs were found to be 0.301-0.672 μg/L, with the linear range of 1.0/2.0-500 μg/L and relative standard deviations of <8.0% (c = 5 μg/L and n = 7). The accuracy of the proposed method was validated by the recovery test, and the recoveries of target BUs in spiked pear juice and pear beverage were 82.0-113 and 84.0-112%, respectively.

Wide-Temperature-Range Li-S Batteries Enabled by Thiodimolybdate [Mo2S12]2- as a Dual-Function Molecular Catalyst for Polysulfide Redox and Lithium Intercalation

In lithium-sulfur batteries, a serious obstacle is the dissolution and diffusion of long-chain polysulfides, resulting in rapid capacity decay and low Coulombic efficiency. At present, a common practice is designing cathode materials to solve this problem, but this gives rise to reduced gravimetric and volumetric energy densities. Herein, we present a thiodimolybdate [Mo₂S₁₂]^2- cluster as sulfur host material that can effectively confine the shuttling of polysulfides and contribute its own capacity in Li-S cells. Moreover, the [Mo₂S₁₂]^2- cluster as a "bidirectional catalyst" can effectively catalyze polysulfide reduction and lithium sulfide oxidation. We further investigate the catalytic mechanism of [Mo₂S₁₂]^2- clusters by theoretical calculations, in situ spectroscopic techniques, and electrochemical studies. The (NH₄)₂Mo₂S₁₂/S cathodes show good electrochemical performance under a wide range of temperatures. In addition, a pouch cell fabricated with (NH₄)₂Mo₂S₁₂/S cathodes maintains a stable output for more than 50 cycles.

Humidity-Independent Artificial Olfactory Array Enabled by Hydrophobic Core-Shell Dye/MOFs@COFs Composites for Plant Disease Diagnosis

As a class of important artificial olfactory system, the colorimetric sensor array possesses great potential for commercialization due to its cost-effectiveness and portability. However, when applied to practical applications, the humidity interference from ambient environment and dissatisfactory sensitivity for trace target VOCs are largely unsolved problems. To overcome the problems, we developed a series of dye/MOFs@COFs gas-sensing materials with core-shell structure using a hydrophobization strategy by encapsulation of dye/metal-organic frameworks (MOFs) into hydrophobic covalent organic frameworks (COFs). Benefiting from the hydrophobic property of the COF shell, the dye/MOFs@COFs composites were endowed with excellent humidity-resistance even under 100% relative humidity (RH). Moreover, due to the uniform distribution of dyes on the porous MOFs, the dye/MOFs@COFs sensors also exhibited improved sensitivity at the sub-ppm level, compared with conventional dye sensors. On basis of the excellent humidity-resistance and improved sensitivity, an artificial olfactory array based on dye/MOFs@COFs composites was proven to be a successful practical application in early and accurate detection of wheat scab (1 day after inoculation) by monitoring its released VOC markers. The synthetic strategy for core-shell dye/MOFs@COFs is applicable to a wide range of colorimetric sensor arrays, endowing them with excellent humidity-resistance and sensitivity for the feasibility of practical applications.

A Ti/Nb-functionalized COF material based on IMAC strategy for efficient separation of phosphopeptides and phosphorylated exosomes

In this work, on the basis of an immobilized metal ion affinity chromatography enrichment strategy, a new kind of covalent organic framework (COF) material for enrichment of phosphorylated peptides and exosomes was successfully prepared in a facile method, and Ti⁴⁺ and Nb⁵⁺ were used as dual-functional ions (denoted as COF-S-S-COOH-Ti⁴⁺/Nb⁵⁺). With the advantage of unbiased enrichment towards phosphopeptides, COF-S-S-COOH-Ti⁴⁺/Nb⁵⁺ shows ultra-high selectivity (maximum molar ratio of β-casein: BSA is 1:20,000) and low limit of detection (0.2 fmol). In addition, the material has an excellent phosphopeptide loading capacity (100 μg/mg) and reusability (at least seven times). Furthermore, applying the material to the actual sample, 4 phosphopeptides were selectively extracted from the serum of renal carcinoma patients. At the same time, exosomes with an intact structure in the serum of renal carcinoma patients were successfully isolated rapidly using this strategy. All experiments have shown that COF-S-S-COOH-Ti⁴⁺/Nb⁵⁺ exhibits exciting potential in practical applications.

Facile preparation of uniform-sized covalent organic framework nanoflowers as versatile sample-pretreatment platforms for sensitive and specific determination of hazardous substances

Covalent-organic frameworks (COFs) have lately received extensive interest for their outstanding performance, especially to adsorption of hazards, while easy-preparation of uniform-sized COFs hold a great challenge. This research presented a simple synthesis method of flower-shaped COF (nanoflower) with strong hydrophobic surface at room temperature. Taking advantage of its easy-prepared and uniform-sized features, we proposed a versatile and efficient sample-pretreatment platform by employing the nanoflower COF for affinity adsorption of various hydrophobic biotoxins and further surface imprinting for selective enrichment of specific biotoxin (COF@MIP), respectively. The COF@MIP was integrating COF with molecular imprinting technique to achieve selective identification of sterigmatocystin (ST) with high specificity and sensitivity. They both exhibited well reusability, preserving 81% of initial activity after being used for six cycles. The as-prepared materials coupled with offline solid phase extraction (SPE) and high performance liquid chromatography (HPLC) were successfully applied to five common cereals with good recoveries in the range of 70.3-100.7%. Moreover, the principle of versatile sample pretreatment and detection platform based on the facile-prepared and uniform-sized COF nanoflower would be easily extended to other hazards. It provided a prospective approach for the pretreatment and determination of hazardous substances with low level in complex sample matrix.

Histostar-Functionalized Covalent Organic Framework for Electrochemical Detection of Exosomes

Covalent organic frameworks (COFs) are gaining growing interest owing to their various structures and versatility. Since their specific physical–chemical characteristics endow them great usage potentiality in biosensing, we herein have synthesized spherical COFs with regular shape and good dispersion, which are further used for the design of a novel nanoprobe by modifying Histostar on the surface of the COFs. Moreover, we have applied a nanoprobe for the fabrication of an electrochemical biosensor to detect exosomes. Since Histostar is a special polymer, conjugated with many secondary antibodies (IgG), and HRP can increase the availability of HRP at the antigenic site, the biosensor can have a strong signal amplification ability. Meanwhile, since COFs with high porosity can be loaded with a huge amount of Histostar, the sensitivity of the biosensor can be further improved. With such a design, the proposed biosensor can achieve a low exosomes detection limit of 318 particles/µL, and a wide linear detection range from 10³ particles/µL to 10⁸ particles/µL. So, this work may offer a promising platform for the ultrasensitive detection of exosomes.

Determination of water in organic solvents and raw food products by fluorescence quenching of a crystalline vinyl-functionalized COF

Covalent organic frameworks (COFs) with good chemical stability, flexible chemical functionalization, tunable pore sizes, and high specific surface areas have been increasingly employed in the field of fluorescence sensing. In this work, a crystalline vinyl-functionalized COF TzDa-V was facilely prepared through a room-temperature synthetic method via condensation reaction between 4,4',4″-(1,3,5-triazine-2,4,6-triyl)trianiline (Tz) and 2,5-diallyloxyterephthalaldehyde (Da-V). The intermolecular charge transfer (ICT) effect endowed the TzDa-V with fluorescence characteristic, and it was sensitive to trace water and can be quenched due to the disruption of ICT process by water. On this base, the prepared COF TzDa-V with excellent chemical/thermal stability was applied to sensing of trace water in common organic solvents such as DMF, acetone, THF, and ethyl acetate with rapid response (less than 10 s), satisfactory sensing range (0.5-18% water in DMF, 0.5-15% water in acetone, 0.5-16% water in THF, 0.5-5% in ethyl acetate, v/v), and high sensitivity. The limits of detection for water in DMF, acetone, THF, and ethyl acetate were 0.0497%, 0.0590%, 0.0502%, and 0.0766% (v/v), respectively. The proposed probe was successfully used for the detection of trace water in food products such as salt and sugar. The COF TzDa-V would be a good candidate for application in water sensing.

Confining enzymes in porous organic frameworks: from synthetic strategy and characterization to healthcare applications

Enzymes are a class of natural catalysts with high efficiency, specificity, and selectivity unmatched by their synthetic counterparts and dictate a myriad of reactions that constitute various cascades in living cells. The development of suitable supports is significant for the immobilization of structurally flexible enzymes, enabling biomimetic transformation in the extracellular environment. Accordingly, porous organic frameworks, including metal organic frameworks (MOFs), covalent organic frameworks (COFs) and hydrogen-bonded organic frameworks (HOFs), have emerged as ideal supports for the immobilization of enzymes because of their structural features including ultrahigh surface area, tailorable porosity, and versatile framework compositions. Specially, organic framework-encased enzymes have shown significant enhancement in stability and reusability, and their tailorable pore opening provides a gatekeeper-like effect for guest sieving, which is beneficial for mimicking intracellular biocatalysis processes. This immobilization technique brings new insight into the development of next-generation enzyme materials and shows huge potential in healthcare applications, such as biomarker diagnosis, biostorage, and cancer and antibacterial therapies. In this review, we describe the state-of-the-art strategies for the structural immobilization of enzymes using the well-explored MOFs and burgeoning COFs and HOFs as scaffolds, with special emphasis on how these porous framework-confined technologies can provide a favorable microenvironment for mimicking natural biocatalysis. Subsequently, advanced characterization techniques for enzyme conformation, the effect of the confined microenvironment on the activity of enzymes, and the emerging healthcare applications will be surveyed.

Core-Shell Carbon-Based Bifunctional Electrocatalysts Derived from COF@MOF Hybrid for Advanced Rechargeable Zn-Air Batteries

The development of highly active carbon-based bifunctional electrocatalysts for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is highly desired, but still full of challenges in rechargeable Zn-air batteries. Metal organic frameworks (MOFs) and covalent organic frameworks (COFs) have gained great attention for various applications due to their attractive features of structural tunability, high surface area and high porosity. Herein, a core-shell structured carbon-based hybrid electrocatalyst (H-NSC@Co/NSC), which contains high density active sites of MOF-derived shell (Co/NSC) and COF-derived hollow core (H-NSC), is successfully fabricated by direct pyrolysis of covalently-connected COF@ZIF-67 hybrid. The core-shell H-NSC@Co/NSC hybrid manifests excellent catalytic properties toward both OER and ORR with a small potential gap (∆E = 0.75 V). The H-NSC@Co/NSC assembled Zn-air battery exhibits a high power-density of 204.3 mW cm^-2 and stable rechargeability, outperforming that of Pt/C+RuO₂ assembled Zn-air battery. Density functional theory calculations reveal that the electronic structure of the carbon frameworks on the Co/NSC shell can be effectively modulated by the embedded Co nanoparticles (NPs), facilitating the adsorption of oxygen intermediates and leading to enhanced catalytic activity. This work will provide a strategy to design highly-efficient electrocatalysts for application in energy conversion and storage.

Biofluids Metabolic Profiling Based on PS@Fe3O4-NH2 Magnetic Beads-Assisted LDI-MS for Liver Cancer Screening

Liver cancer (LC) is the third frequent cause of death worldwide, so early diagnosis of liver cancer patients is crucial for disease management. Herein, we applied NH₂-coated polystyrene@Fe₃O₄ magnetic beads (PS@Fe₃O₄-NH₂ MBs) as a matrix material in laser desorption/ionization mass spectrometry (LDI-MS). Rapid, sensitive, and selective metabolic profiling of the native biofluids was achieved without any inconvenient enrichment or purification. Then, based on the selected m/z features, LC patients were discriminated from healthy controls (HCs) by machine learning, with the high area under the curve (AUC) values for urine and serum assessments (0.962 and 0.935). Moreover, initial-diagnosed and subsequent-visited LC patients were also differentiated, which indicates potential applications of this method in early diagnosis. Furthermore, among these identified compounds by FT-ICR MS, the expression level of some metabolites changed from HCs to LCs, including 29 and 12 characteristic metabolites in human urine and serum samples, respectively. These results suggest that PS@Fe₃O₄-NH₂ MBs-assisted LDI-MS coupled with machine learning is feasible for LC clinical diagnosis.

Landscaping Covalent Organic Framework Nanomorphologies

The practical utilization of covalent organic frameworks (COFs) with manipulation at the atomic and molecular scale often demands their assembly on the nano-, meso-, and macroscale with precise control. Consequently, synthetic approaches that establish the ability to control the nucleation and growth of COF crystallites and their self-assembly to desired COF nanomorphologies have drawn substantial attention from researchers. On the basis of the dimensionality of the COF morphologies, we can categorize them into zero- (0-D), one- (1-D), two- (2-D), and three-dimensional (3-D) nanomorphologies. In this perspective, we summarize the reported synthetic strategies that enable precise control of the COF nanomorphologies' size, shape, and dimensionality and reveal the impact of the dimensionalities in their physicochemical properties and applications. The aim is to establish a synergistic optimization of the morphological dimensionality while keeping the micro- or mesoporosity, crystallinity, and chemical functionalities of the COFs in perspective. A detailed knowledge along the way should help us to enrich the performance of COFs in a variety of applications like catalysis, separation, sensing, drug delivery, energy storage, etc. We have discussed the interlinking between the COF nanomorphologies via the transmutation of the dimensionalities. Such dimensionality transmutation could lead to variation in their properties during the transition. Finally, the concept of constructing COF superstructures through the combination of two or more COF nanomorphologies has been explored, and it could bring up opportunities for developing next-generation innovative materials for multidisciplinary applications.

Recent Advances in the Application of Covalent Organic Frameworks in Extraction: A Review

Covalent organic frameworks (COFs) are a class of emerging materials that are synthesized based on the covalent bonds between different building blocks. COFs possess unique attributes in terms of high porosity, tunable structure, ordered channels, easy modification, large surface area, and great physical and chemical stability. Due to these features, COFs have been extensively applied as adsorbents in various extraction modes. Enhanced extraction performance could be reached with modified COFs, where COFs are presented as composites with other materials including nanomaterials, carbon and its derivatives, silica, metal-organic frameworks, molecularly imprinted polymers, etc. This review article describes the recent advances, developments, and applications of COF-based materials being utilized as adsorbents in the extraction methods. The COFs, their properties, their synthesis approaches as well as their composite structures are reviewed. Most importantly, suggested mechanisms for the extraction of analyte(s) by COF-based materials are also discussed. Finally, the current challenges and future prospects of COF-based materials in extraction methods are summarized and considered in order to provide more insights into this field.

Zinc-Air Battery-Assisted Self-Powered PEC Sensors for Sensitive Assay of PTP1B Activity Based on Perovskite Quantum Dots Encapsulated in Vinyl-Functionalized Covalent Organic Frameworks

The self-powered sensors have attracted widespread attention in the analysis field due to a huge demand of point-of-care testing (POCT) in the early diagnosis of diseases. However, the output voltage of the reported self-powered sensors is always small, resulting in a narrow linear detection range and low assay sensitivity. Herein, a self-powered photoelectrochemical (PEC) sensor with zinc-air batteries as a power source was developed for activity assay of protein tyrosine phosphatase 1B (PTP1B) based on perovskite quantum dots encapsulated in the vinyl-functionalized covalent organic framework (COF-V). CsPbBr₃ nanocrystals were stabilized by the confinement effect of the COF-V cage without aggregation, and the resulting CsPbBr₃@COF-V composite was used as the cathodic photoelectric material to construct the zinc-air battery with a large open-circuit voltage (OCV, 1.556 V). Before PTP1B activity assay, an auxiliary peptide-polyamidoamine-phosphopeptide (P2-PAMAM-P1) hybrid was introduced into the photocathode via thiol-ene click reaction between the thiol group on the P1 and the vinyl group on the COF-V. The steric hindrance effect of the P1-PAMAM-P2 hybrid inhibited the PEC performance of the photocathode, resulting in a small OCV of the zinc-air battery. When the PTP1B existed, PTP1B-catalyzed dephosphorylation of tyrosine on P1 facilitated the cleavage process of P1 by chymotrypsin, leading to the removal of the P2-PAMAM-P1 hybrid from the photocathode and consequently the enhancement of the OCV. Therefore, the activity of PTP1B was sensitively detected. The developed self-powered PEC sensor showed superior performance for PTP1B activity assay (broad linear response range, 0.1 pM to 10 nM and low detection limit, 0.032 pM) due to the large output voltage of the constructed zinc-air battery and has great potential in POCT of protein phosphatase-related diseases and the discovery of protein phosphatase-targeted drugs.

Covalent Organic Framework Nanoplates Enable Solution-Processed Crystalline Nanofilms for Photoelectrochemical Hydrogen Evolution

As covalent organic frameworks (COFs) are coming of age, the lack of effective approaches to achieve crystalline and centimeter-scale-homogeneous COF films remains a significant bottleneck toward advancing the application of COFs in optoelectronic devices. Here, we present the synthesis of colloidal COF nanoplates, with lateral sizes of ∼200 nm and average heights of 35 nm, and their utilization as photocathodes for solar hydrogen evolution. The resulting COF nanoplate colloid exhibits a unimodal particle-size distribution and an exceptional colloidal stability without showing agglomeration after storage for 10 months and enables smooth, homogeneous, and thickness-tunable COF nanofilms via spin coating. Photoelectrodes comprising COF nanofilms were fabricated for photoelectrochemical (PEC) solar-to-hydrogen conversion. By rationally designing multicomponent photoelectrode architectures including a polymer donor/COF heterojunction and a hole-transport layer, charge recombination in COFs is mitigated, resulting in a significantly increased photocurrent density and an extremely positive onset potential for PEC hydrogen evolution (over +1 V against the reversible hydrogen electrode), among the best of classical semiconductor-based photocathodes. This work thus paves the way toward fabricating solution-processed large-scale COF nanofilms and heterojunction architectures and their use in solar-energy-conversion devices.

Phosphorylation of covalent organic framework nanospheres for inhibition of amyloid-β peptide fibrillation

The development and exploration of new nanostructural inhibitors against Alzheimer's disease (AD)-associated amyloid-β (Aβ) fibrillation have attracted extensive attention and become a new frontier in nanomedicine. However, focusing on finding an effective nanostructure is one of the most challenging parts of the therapeutics task. Herein, nanoscale spherical covalent organic frameworks (COFs) via post-synthetic functionalization with sodium phosphate (SP) groups on the channel networks were found to efficiently inhibit Aβ fibrillation. The as-prepared uniform SP-COF nanospheres with high surface area, good crystallinity, and chemical stability were characterized by multifarious microscopic and spectroscopic techniques. Moreover, molecular dynamics simulation together with fibrillation kinetics and cytotoxicity assay experiments shows that there were restricted-access adsorption channels in the SP-COFs which were formed by the cavities with size and functional groups accommodated to the Aβ peptide sequence and significantly affected the fibrillation and cytotoxicity of Aβ. Transmission electron microscopy (TEM), dynamic light scattering (DLS) monitoring, isothermal titration calorimetry (ITC), Fourier transform infrared (FT-IR) and circular dichroism (CD) spectra measurements, and confocal imaging observation were performed to understand the inhibition mechanism and influencing factors of the SP-COFs. To our knowledge, our strategy is the first exploration of COF-based anti-amyloidogenic nanomaterials with high affinity and specific targeting, which are crucial for the inhibition of Aβ fibrillation for AD prevention and treatment.

Nanoscale spherical COFs via phosphorylation functionalization were found to efficiently inhibit fibrillation of the Alzheimer's disease-associated Aβ peptide.

Top-Down Rational Engineering of Heteroatom-Doped Graphene Quantum Dots for Laser Desorption/Ionization Mass Spectrometry Detection and Imaging of Small Biomolecules

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) is widely applied in mapping macrobiomolecules in tissues, but it is still limited in profiling low-molecular-weight (MW) compounds (typically metabolites) due to ion interference and suppression by organic matrices. Here, we present a versatile "top-down" strategy for rational engineering of carbon material-based matrices, by which heteroatom-doped graphene quantum dots (HGQDs) were manufactured for LDI MS detection and imaging of small biomolecules. The HGQDs derived from parent materials inherited the π-conjugated networks and doping sites for promoting energy transfer and negative ion generation, while their extremely small size guaranteed the matrix uniformity and signal reproducibility in LDI MSI. Compared to other HGQDs, nitrogen-doped graphene quantum dots (NGQDs) exhibited superior capability of assisting LDI of various small molecules, including amino acids, fatty acids, saccharides, small peptides, nucleobases, anticancer drugs, and bisphenol pollutants. Density functional theory simulations also corroborated that the LDI efficiency was markedly raised by the proton-capturing pyridinic nitrogen species and compromised by the electron-deficient boron dopants. NGQDs-assisted LDI MS further enabled label-free investigation on enzyme kinetics using an ordinary short peptide as the substrate. Moreover, due to the high salt tolerance and signal reproducibility, the proposed negative-ion NGQDs-assisted LDI MSI was able to reveal the abundance and distribution of low-MW species in rat brain tissue and achieved the imaging of low-MW lipids in coronally sectioned rat brains subjected to traumatic brain injury. Our work offers a new route for customizing nanomaterial matrices toward LDI MSI of small biomolecules in biomedical and pathological research.

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.

Amorphous-to-Crystalline Transformation: General Synthesis of Hollow Structured Covalent Organic Frameworks with High Crystallinity

Morphological control of covalent organic frameworks (COFs) is particularly interesting to boost their applications; however, it remains a grand challenge to prepare hollow structured COFs (HCOFs) with high crystallinity and uniform morphology. Herein, we report a versatile and efficient strategy of amorphous-to-crystalline transformation for the general and controllable fabrication of highly crystalline HCOFs. These HCOFs exhibited ultrahigh surface areas, radially oriented nanopore channels, quite uniform morphologies, and tunable particle sizes. Mechanistic studies revealed that H₂O, acetic acid, and solvent played a crucial role in manipulating the hollowing process and crystallization process by regulating the dynamic imine exchange reaction. Our approach was demonstrated to be applicable to various amines and aldehydes, producing up to 10 kinds of HCOFs. Importantly, based on this methodology, we even constructed a library of unprecedented HCOFs including HCOFs with different pore structures, bowl-like HCOFs, cross-wrinkled COF nanocapsules, grain-assembled HCOFs, and hydrangea-like HCOFs. This strategy was also successfully applied to the fabrication of COF-based yolk-shell nanostructures with various functional interior cores. Furthermore, catalytically active metal nanoparticles were implanted into the hollow cavities of HCOFs with tunable pore diameters, forming attractive size-selective nanoreactors. The obtained metal@HCOFs catalysts showed enhanced catalytic activity and outstanding size-selectivity in hydrogenation of nitroarenes. This work highlights the significance of nucleation-growth kinetics of COFs in tuning their morphologies, structures, and applications.

Functionalization of Covalent Organic Frameworks with DNA via Covalent Modification and the Application to Exosomes Detection

The functionalization of covalent organic frameworks (COFs) with biomacromolecules can extend their functions, which is the premise of their application in biomedical research. However, strategies to functionalize COFs with biomacromolecules, which can ensure the stability in complex medium and minimize the undesired effects, are still lacking. In this work, we have proposed a strategy to functionalize COFs with DNA by covalently linking DNA to the functional group on the COF surface through Cu(I)-catalyzed azide/alkyne cycloaddition (CuAAC) reaction. The as-prepared DNA-functionalized COFs (DNA-COFs) can exhibit good hybridization ability and cargo loading ability; thus, we have designed a DNA-COF-based nanoprobe and then fabricated an electrochemical biosensor for the detection of exosomes. In this design, the functionalization with DNA enables COFs to recognize and capture exosomes, and the encapsulation of a large number of methylene blue (MB) in COFs facilitates signal amplification, which can enhance the sensitivity of the biosensor. Moreover, by simply replacing the oligonucleotide sequences, the strategy proposed here can generally be used to build different DNA-COFs with diverse functions for broader biomedical applications.

Covalent organic framework-based solid phase microextraction coupled with electrospray ionization mass spectrometry for sensitive screening and quantitative evaluation of carbamazepine and its metabolite in mice

Carbamazepine (CBZ) and its metabolite carbamazepine-10,11-epoxide (CBZEP) play vital role in the treatment of epilepsy. It is of great importance to develop a method for rapid and sensitive monitoring of CBZ and CBZEP due to their narrow therapeutic index. Herein, an imine-linked-based covalent organic framework was synthesized by using 1,3,5-tris (4-aminophenyl) benzene (TPB) and 1,3,5-triformylbenzene (TFB) (denoted as TPB-TFB-COF)，and applied as a solid-phase microextraction (SPME) probe for extracting CBZ and CBZEP. The TPB-TFB-COF showed large surface areas (371 m² g^-1), high regular porosity (1.23 nm) and extraordinary stability, which rendered it an ideal adsorbent for highly efficient enrichment of CBZ and CBZEP. Accordingly, an attractive strategy of the combination of the TPB-TFB-COF-based SPME probe and electrospray ionization mass spectrometry system (ESI/MS) was proposed for rapid screening and sensitive monitoring of CBZ and CBZEP. Under the optimized parameters, the developed method exhibited good linearity for CBZ and CBZEP in the range of 4-1000 μg L^-1 with correlation coefficient (r) no less than 0.9953, and the corresponding limits of detection (LODs) were 0.4 and 2.5 μg L^-1, respectively. Moreover, high enrichment factors (EFs, 202-351 folds) and satisfactory relative standard deviations (RSDs) of one probe (3.3-5.1%) and probe-to-probe (4.8-5.6%) were obtained. By using the proposed method, sensitive screening and quantitative evaluation of CBZ and CBZEP in mice whole blood and tissue homogenates were successfully achieved, indicating the promising applicability of the TPB-TFB-COF-SPME-AMIS as a powerful tool for drug monitoring.

Mixed matrix of MOF@COF hybrids for enrichment and determination of phenoxy carboxylic acids in water and vegetables

A novel mixed matrix of MOF@COF hybrid was firstly formed by coating of hexahedral cage structure MOF with lightweight porous COF, and applied in dispersive solid-phase extraction of the phenoxy carboxylic acids (PCAs) from water and vegetable samples. Combined with liquid chromatography-tandem mass spectrometry, an excellent method with low limits of detection (0.69-1.79 ng·L^-1/0.002-0.006 ng·g^-1), good reproducibility (1.32%-7.02%/1.81%-6.71%), and excellent linearities (10-1000 ng·L^-1, R ≥ 0.9955/0.04-50 ng·g^-1, R ≥ 0.9966) was established. The adsorption mechanisms deduced that the π-π interaction, hydrophobic effects, hydrogen bond, and halogen bond may promote the excellent adsorption of the PCAs. Finally, the applicability of the method was verified by spiking four kinds of water and vegetable samples with PCAs, and satisfying recoveries were obtained (between 83.3% and 104.9%).

Aspartic Acid-Assisted Size-Controllable Synthesis of Nanoscale Spherical Covalent Organic Frameworks with Chiral Interfaces for Inhibiting Amyloid-β Fibrillation

Covalent organic framework nanospheres (COF NSs) have garnered special attention due to their uniform sphere morphology, adjustable particle size, and mesoporous microenvironment. However, methods to control an optimal particle size scale while achieving solution dispersibility and specific surface properties remain underdeveloped, which precludes many of the biomedical applications. Here, we propose and develop a general strategy to access simultaneous size control and surface functionalization of uniform spherical COF NSs in a single step using aspartic acid (d-/l-Asp) that plays center roles in an acid catalyst, hydrophilicity, size-controllable synthesis, and chiral enantiomer. In this study, for the first time, we have employed a surface chemistry engineering study to create a variety of nanoscale spherical COFs and subsequently measure parameters to evaluate the effectiveness of Asp in the regulation of the particle size. Moreover, the potential utilization of the d/l-enantiomeric Asp-COF NSs in preventing β-amyloid (Aβ) aggregation is investigated by analyzing their interactions with Aβ amyloids using a multitechnique experimental approach. To our knowledge, our strategy is the first synthesis of hydrophilic COF NSs with an optimal length scale and a chiral-selective targeting surface, which are crucial for the inhibition of Aβ fibrillation for Alzheimer's disease prevention.

SERS Detection of Benzoic Acid in Milk by Using Ag-COF SERS Substrate

Benzoic acid, which has a pivotal role in food additive, is prohibited to add as a preservative in dairy products. China, Brazil, and other countries have proposed standard methods to detect the addition of benzoic acid in food. Surface-enhanced Raman scattering (SERS) is an upcoming spectral detection technique, which has been widely used in the field of material analysis with the advantages of non-invasive, fast detection speed and complex environment with little interference. To detect the illegal use of benzoic acid in dairy industry, we developed Ag-COF (covalent-organic framework) material as SERS substrate to detect benzoic acid in liquid milk. The great enhancement ability of Ag-COF substrate is controlled by the addition of acetic acid and complex interplay between COF material and benzoic acid. This detection method has high sensitivity and reliability that allows us to achieve limit of detection (LOD) of 0.13 μg/mL in milk and 0.00372 μg/mL in water by applying this method. In experiment on recovery rate of real samples, the detection time is less than 15 minutes and the relative standard deviation (RSD) ranged from 2.82% to 5.69%. Therefore, this method has practical significance of the detection of benzoic acid in dairy products.

Efficient extraction of trace organochlorine pesticides from environmental samples by a polyacrylonitrile electrospun nanofiber membrane modified with covalent organic framework

Detecting and analyzing of the trace organochlorine pesticides (OCPs) in the real water has become a big challenge. In this work, a novel functional electrospun nanofiber membrane (PAN@COFs) was synthesized through the in situ growth of covalent organic frameworks (COFs) on a polyacrylonitrile electrospun nanofiber membranes under room temperature and used in the solid-phase micro-extraction (SPME) to enrich trace organochlorine pesticides (OCPs) in water. The resulted PAN@COFs composite consisted of numerous nanofibers coated ample porous COFs spheres (~ 500 nm) and owned stable crystal structure, abundant functional groups, good stability. In addition, the enrichment experiments clearly revealed that PAN@COFs exhibited rather outstanding performance on adsorbing the trace OCPs (as low as 10 ng L^-1) with the enrichment of 482-2686 times. Besides, PAN@COFs displayed good reusability and could be reused 100 times. Notably, in the real water samples (sea water and river water), the high enrichment factors and recovery rates strongly confirmed the feasibility of PAN@COFs for detecting the trace OCPs. Furthermore, due to the synergy of π-π stacking interaction and hydrophobic interaction between the OCPs molecules and PAN@COFs, the OCPs could be efficiently adsorbed on PAN@COFs, even under the extremely low driving force.

Visual naked-eye detection of SARS-CoV-2 RNA based on covalent organic framework capsules

The ongoing outbreak of coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has highlighted that new diagnosis technologies are crucial for controlling the spread of the disease. Especially in the resources-limit region, conveniently operated detection methods such as "naked-eye" detection are urgently required that no instrument is needed. Herein, we have designed a novel and facile strategy to fabricate covalent organic framework (COF) capsules, which can be utilized to establish a new colorimetric assay for naked-eye detection of SARS-CoV-2 RNA. Specifically, we employ the digestible ZIF-90 as the sacrificial template to prepare the hollow COF capsules for horseradish peroxidase (HRP) encapsulation. The fabricated COF capsules can provide an appropriate microenvironment for the enzyme molecules, which may improve the conformational freedom of enzymes, enhance the mass transfer, and endow the enzyme with high environmental resistance. With such design, the proposed assay exhibits outstanding analytical performance for the detection of SARS-CoV-2 RNA in the linear range from 5 pM to 50 nM with a detection limit of 0.28 pM which can go parallel to qTR-PCR analysis. Our method also possesses excellent selectivity and reproducibility. Moreover, this method can also be served to analyze the clinical samples, and can successfully differentiate COVID-19 patients from healthy people, suggesting the promising potential in clinical diagnosis.

Surfactant-free synthesis of covalent organic framework nanospheres in water at room temperature

Covalent organic frameworks (COFs) are a new class of porous materials receiving much attention due to their unique characteristics. However, COFs have been usually synthesized under harsh and complicated conditions, limiting their practical applications. We propose a surfactant-free strategy to controllably synthesize an imine-based covalent organic framework (COF) nanomaterial in water at room temperature. Introduction of tiny amounts of co-solvents not only achieves the morphology and size control of COFs but also ensures stability of COF nanomaterials in aqueous solution. Moreover, water as a solvent plays an important role in the size adjustment of COFs. The surface area of the obtained COFs was approximately 398 m²/g with a pore size distribution of about 2.8 nm. In addition, the COFs displayed a good crystallinity.

Covalent organic framework-V modified porous polypropylene hollow fiber with detachable dumbbell-shaped structure for stir bar sorptive extraction of benzophenones

Polypropylene hollow fiber is a kind of ideal material for stir bar sorptive extraction (SBSE) which possesses the advantages of porous structure, large specific surface area, high mechanical strength, and good solvent resistance. In this work, a novel SBSE device using the polypropylene hollow fiber-based stir bar with the detachable dumbbell-shaped structure was designed and prepared. Covalent organic framework-V (COF-V), which possesses porous structure, sphere shape with large specific surface area, was synthesized at room temperature and grown on polypropylene hollow fiber by polydopamine modification method. Compared with previous studies which used etched poly(ether ether ketone) as supporting material, polypropylene hollow fiber omitted the complicated, difficult and dangerous pretreatment process with high concentrated sulfuric acid. The immobilization of COF-V on the polypropylene hollow fiber significantly endows them with multiple interaction abilities including hydrophobic interaction and π-π interaction. The stir bar showed good performance and stability for the extraction of four benzophenones including BP-1, BP-6, BP-3 and Ph-BP. By coupling with HPLC-UV, the COF-V@polypropylene hollow fiber based SBSE method showed wide linear range (0.1-200 ng/mL), excellent linearity (R² ≥ 0.9979), high sensitivity (LODs in the range of 0.02-0.03 ng/mL), and good repeatability (RSD ≤ 5.21%). This method was successfully applied to the analysis of benzophenones in soil and sunscreen samples.

Emerging porous organic polymers for biomedical applications

This review summarizes and discusses the recent progress in porous organic polymers for diverse biomedical applications such as drug delivery, biomacromolecule immobilization, phototherapy, biosensing, bioimaging, and antibacterial applications.

Controllable synthesis of uniform large-sized spherical covalent organic frameworks for facile sample pretreatment and as naked-eye indicator

The successful application of covalent organic frameworks (COFs) depends on not only their unique chemical structures but also their morphology, size, and architecture. Spherical COFs (SCOFs) are attracted special attention due to the superiority of spherical materials in many applications. However, the synthesis of uniform large-sized SCOFs remains a challenge. Herein, by carefully optimizing the synthesis of a heteropore COF, we find that solvent type and catalyst concentration play important roles in determining the morphology and size of COFs, and eventually achieve the controllable synthesis of large SCOFs with uniform sizes ranging from 200 μm to 5 mm. The obtained SCOFs keep the dual-pore feature of the heteropore COF and show good stability and high crystallinity. To exhibit the superior application potential of SCOFs, the SCOFs with a size range of 200-300 μm were demonstrated to be promising solid-phase extraction (SPE) fillers. As-prepared SCOFs-packed SPE column could effectively remove ≥99% phytochrome matrix from 6 different vegetable samples in 10 s, accompanied by 72.56-112.37% recoveries of 33 chemical hazards with different physicochemical properties, thus showing greatly promising application prospects in sample pretreatment of nontargeted food safety analysis. By utilizing acid/base-adjusted reversible color change, millimeter-sized SCOFs were developed as an easy-to-operate and reusable naked-eye indicator of acids.