A covalent organic framework nanosheet-based electrochemical aptasensor with sensitive detection performance

Target-driven cascade amplified assembly of covalent organic frameworks on tetrahedral DNA nanostructure with multiplex recognition domains for ultrasensitive detection of microRNA

BACKGROUND

MicroRNA (miRNA) emerges as important cancer biomarker, accurate detection of miRNA plays an essential role in clinical sample analysis and disease diagnosis. However, it remains challenging to realize highly sensitive detection of low-abundance miRNA. Traditional detection methods including northern blot and real-time PCR have realized quantitative miRNA detection. However, these detection methods are involved in sophisticated operation and expensive instruments. Therefore, the development of novel sensing platform with high sensitivity and specificity for miRNA detection is urgently demanded for disease diagnosis.

RESULTS

In this work, a novel electrochemical biosensor was constructed for miRNA detection based on target-driven cascade amplified assembly of electroactive covalent organic frameworks (COFs) on tetrahedral DNA nanostructure with multiplex recognition domains (m-TDN). COFs were employed as nanocarriers of electroactive prussian blue (PB) molecules by the "freeze-drying-reduction" method without the use of DNA as gatekeeper, which was simple, mild and efficient. The target-triggered catalytic hairpin assembly (CHA) and glutathione reduction could convert low-abundance miRNA into a large amount of Mn2+. Without the addition of exogenous Mn2+, the dynamically-generated Mn2+-powered DNAzyme cleavage process induced abundant PB-COFs probe assembled on the four recognition domains of m-TDN, resulting in significantly signal output. Using miRNA-182-5p as the model target, the proposed electrochemical biosensor achieved ultrasensitive detection of miRNA-182-5p in the range of 10 fM-100 nM with a detection limit of 2.5 fM.

SIGNIFICANCE AND NOVELTY

Taking advantages of PB-COFs probe as the enhanced signal labels, the integration of CHA, Mn2+-powered DNAzyme and m-TDN amplification strategy significantly improved the sensitivity and specificity of the biosensor. The designed sensing platform was capable of miRNA detection in complex samples, which provided a new idea for biomarker detection, holding promising potential in clinical diagnosis and disease screening.

Effective separation of dyes/salts by sulfonated covalent organic framework membranes based on phenolamine network conditioning

This study developed a modified polyacrylonitrile (PAN) membrane controlled by a phenol-amine network and enhanced with a sulfonated covalent organic framework (SCOF), aimed at improving the efficiency of textile wastewater treatment. Utilizing a phenol-amine network control strategy allows for precise manipulation of interfacial reactions in the synthesis of SCOF, achieving highly uniform modification on the surface of the PAN membrane. This modified membrane demonstrated high rejection of over 98% for various water-soluble dyes, including Alcian blue 8GX, Coomassie Brilliant Blue G250, methyl blue, congo red, and rose bengal, and also exhibited specific selectivity in processing salt-containing wastewater. By adjusting the deposition time of the phenol-amine and the concentration of SCOF monomers, optimal retention performance and permeate flux were achieved, effectively separating dyes and salts. This research provides a new and effective solution for treating textile wastewater, especially in separating and recovering dyes and salts, offering broad application prospects in environmental management and water resource management, and highlighting its significant practical implications.

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

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

Aptasensor based on high surface area covalent organic framework for simple and ultrasensitive detection of sarcosine in the diagnosis of prostate cancer

In this study, an electrochemical aptasensor was developed for the specific detection of sarcosine using a covalent organic framework (COF). The imine-based two-dimensional COF was synthesized through a solvothermal process using terephthaldehyde and melamine. This resulted in the formation of a structure that is highly porous and has a unique surface area of 908 m2/g. The produced biosensor demonstrated a significant linear relationship between charge transfer resistance (Rct) and various concentrations of sarcosine in blood serum samples. The aptasensor had two linear ranges, spanning from 0.5 fM to 700 fM and 10 pM to 0.12 nM, respectively, with a detection limit of 0.15 fM. The incorporation of high surface area COFs in the aptasensor design offers a promising combination of sensitivity, stability, and specificity. This combination creates a valuable device for diagnosing and monitoring of prostate cancer and potentially other diseases.

Not Only Graphene Two-Dimensional Nanomaterials: Recent Trends in Electrochemical (Bio)sensing Area for Biomedical and Healthcare Applications

Two-dimensional (2D) nanomaterials (e.g., graphene) have attracted growing attention in the (bio)sensing area and, in particular, for biomedical applications because of their unique mechanical and physicochemical properties, such as their high thermal and electrical conductivity, biocompatibility, and large surface area. Graphene (G) and its derivatives represent the most common 2D nanomaterials applied to electrochemical (bio)sensors for healthcare applications. This review will pay particular attention to other 2D nanomaterials, such as transition metal dichalcogenides (TMDs), metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and MXenes, applied to the electrochemical biomedical (bio)sensing area, considering the literature of the last five years (2018-2022). An overview of 2D nanostructures focusing on the synthetic approach, the integration with electrodic materials, including other nanomaterials, and with different biorecognition elements such as antibodies, nucleic acids, enzymes, and aptamers, will be provided. Next, significant examples of applications in the clinical field will be reported and discussed together with the role of nanomaterials, the type of (bio)sensor, and the adopted electrochemical technique. Finally, challenges related to future developments of these nanomaterials to design portable sensing systems will be shortly discussed.

Covalent organic framework-based immunosensor to detect plasma Latexin reveals novel biomarker for coronary artery diseases

It is a great challenge to develop an efficient and rapid method to detect of biomarkers of cardiovascular disease. In this research, a differential pulse voltammetry (DPV)-based ultrasensitive immunosensor for the detection of plasma Latexin (LXN) has been established. With the aim to increase the surface area of the bare glassy carbon electrode (GCE), multi-walled carbon nanotube-graphene oxide has been developed. Covalent organic frameworks (COFs) are dropped with gold nanoparticles (AuNPs), secondary antibody and thionine (Thi-Ab2-Au-COFs) act as the signal probe with high electronic conductivity. Under the ideal conditions, the immunosensor displayed a broad linear response range from 0.01 ng mL-1 to 100 ng mL-1, with a detection limit of 50 pg mL-1 (S/N = 3). The immunosensor also demonstrates outstanding sensitivity, repeatability, and stability. Finally, we utilized the designed immunosensor to detect plasma LXN in coronary artery disease (CAD) patients, and the data showed that plasma LXN was significantly increased in CAD patients with a good performance of ROCAUC (AUC 0.871, 95 % CI 0.725-1.0, p = 0.002), indicating plasma LXN is a potential biomarker of cardiovascular disease. This immunosensor is a promising strategy for screening CAD patients in clinical practice.

A homogeneous label-free electrochemical aptasensor based on an omega-like DNA nanostructure for progesterone detection

A novel homogeneous label-free electrochemical aptamer sensor for the detection of progesterone was prepared by combining a well-designed omega (Ω)-like DNA (Ω-DNA) nanostructure, with an isothermal cycling amplification strategy based on the highly efficient exonuclease III (Exo III). The omega-like (Ω) DNA is composed of two oligonucleotide strands: DNA1 and DNA2. The Pro aptamer triggers a chain displacement reaction of Ω-DNA nanostructures, forms a new double-stranded DNA structure (aptamer precursor-DNA2), and releases DNA1. Then, Exo III selectively cleaves the DNA duplex and releases the Pro aptamer to participate in a new displacement reaction. Meanwhile, the released DNA1 strands gain access to the strongly bound hemin, forming a hemin/G-quadruplex (DNAzyme). In the presence of hydrogen peroxide (H2O2), differential pulse voltammetry (DPV) was used to detect the current signal from the oxidation of o-phenylenediamine (OPD) to aminoazobenzene (DAP) catalyzed by DNAzyme. However, the amount of released DNA1 from the Ω-DNA nanostructures is reduced in the presence of the target Pro, and the DPV signal declines because of the small amount of DNAzyme formed. The developed electrochemical aptasensor has a wide dynamic linear relationship in the range of 1 pg mL-1 to 10 ng mL-1 under optimal conditions. Its detection limit is down to 0.3 pg mL-1, providing a potential platform for a sensitive Pro assay among electrochemical assays.

Size-controlling preparation of covalent organic framework nanospheres for electrochemical impedimetric aptasensing of oxytetracycline

Covalent organic framework (COF) nanospheres with controlled size of ∼500 and ∼1100 nm were successfully prepared by adjusting the HOAc amount in the synthetic system. The as-synthesized COFs have large conjugate aromatic skeleton, excellent stability, abundant pore, and uniform morphology. These advantages of COFs are benefit for immobilizing aptamers to fabricate the targeted electrochemical aptasensor. The commonly used oxytetracycline (OTC) is an analytic model to explore the sensing performance of the COF-based aptasensor, indicating that the smaller COF (∼500 nm) is more conducive to acquiring the sensitive sensor than that of the larger COF (∼1100 nm). Moreover, the limitation of detection of the COF (∼500 nm)-based aptasensor is calculated to be 7.4 fg mL^-1 using the response impedance signal. Additionally, the aptamer-based biosensor has fine reproducibility, good stability, excellent specificity, and available usability even in real samples.

Ultrasensitive electrochemical aptasensor with Nafion-stabilized f-MWCNTs as signal enhancers for OTA detection

In this study, an ultrasensitive electrochemical (EC) aptasensor with Nafion-stabilized functionalized multi-walled carbon nanotubes (f-MWCNTs) as signal enhancers was established for ochratoxin A (OTA) determination. Herein, f-MWCNTs were prepared through functionalization with nitric acid. The incorporation of Nafion promoted a good dispersion of f-MWCNTs and prevented their leaching on the electrode, making a robust stability of the aptasensor. The Nafion-f-MWCNTs composites were used as the sensing substrates to largely enhance the electroactive surface area and the conductivity of the electrode, realizing a significant signal amplification. Carboxyl groups on the surface of f-MWCNTs readily exposed from Nafion membrane to couple with streptavidin, facilitating the immobilization of biotinylated aptamers to achieve selective recognition towards OTA. When OTA existed, aptamers preferentially combined with it, causing a noticeable decline in the current response. Under optimum conditions, a good linear relationship between the current changes and the logarithm of OTA concentration was observed from 0.005 ng/mL to 10 ng/mL, with a limit of detection low to 1 pg/mL for OTA. The specific, sensitive, and reproducible aptasensor succeeded in application in malt samples, confirming a great promise for more contaminants and providing a universal platform in complex matrices by simply replacing the corresponding aptamers.

Bending Resistance Covalent Organic Framework Superlattice: "Nano-Hourglass"-Induced Charge Accumulation for Flexible In-Plane Micro-Supercapacitors

Covalent organic framework (COF) film with highly exposed active sites is considered as the promising flexible self-supported electrode for in-plane micro-supercapacitor (MSC). Superlattice configuration assembled alternately by different nanofilms based on van der Waals force can integrate the advantages of each isolated layer to exhibit unexpected performances as MSC film electrodes, which may be a novel option to ensure energy output. Herein, a mesoporous free-standing A-COF nanofilm (pore size is 3.9 nm, averaged thickness is 4.1 nm) with imine bond linkage and a microporous B-COF nanofilm (pore size is 1.5 nm, averaged thickness is 9.3 nm) with β-keto-enamine-linkages are prepared, and for the first time, we assembly the two lattice matching films into sandwich-type superlattices via layer-by-layer transfer, in which ABA-COF superlattice stacking into a "nano-hourglass" steric configuration that can accelerate the dynamic charge transportation/accumulation and promote the sufficient redox reactions to energy storage. The fabricated flexible MSC-ABA-COF exhibits the highest intrinsic CV of 927.9 F cm-3 at 10 mV s-1 than reported two-dimensional alloy, graphite-like carbon and undoped COF-based MSC devices so far, and shows a bending-resistant energy density of 63.2 mWh cm-3 even after high-angle and repeat arbitrary bending from 0 to 180°. This work provides a feasible way to meet the demand for future miniaturization and wearable electronics.

Electrochemical Aptasensor Based on Au Nanoparticles Decorated Porous Carbon Derived from Metal-Organic Frameworks for Ultrasensitive Detection of Chloramphenicol

A facile and sensitive electrochemical aptamer sensor (aptasensor) based on Au nanoparticles-decorated porous carbon (AuNPs/PC) composite was developed for the efficient determination of the antibiotic drug chloramphenicol (CAP). AuNPs modified metal-organic framework (AuNPs/ZIF-8) is applied as a precursor to synthesize the porous carbon with homogeneous AuNPs distribution through a direct carbonization step under nitrogen atmosphere. The as-synthesized AuNPs/PC exhibits high surface area and improved conductivity. Moreover, the loading AuNPs could enhance the attachment of the aptamers on the surface of electrode through the Au–S bond. When added to CAP, poorly conductive aptamer-CAP complexes are formed on the sensor surface, which increases the hindrance to electron transfer resulting in a decrease in electrochemical signal. Based on this mechanism, the developed CAP aptasensor represents a wide linear detection range of 0.1 pM to 100 nM with a low detection limit of 0.03 pM (S/N = 3). In addition, the proposed aptasensor was employed for the analysis of CAP in honey samples and provided satisfactory recovery.