Nb 4 C 3 T x (MXene)/Au/DNA Aptasensor for the Ultraselective Electrochemical Detection of Lead in Water Samples

A highly selective and sensitive electrochemical sensor for tetracycline resistant genes detection based on the non-covalent interaction of graphene oxide and nucleobase

Antibiotic resistance genes (ARGs) are causing worldwide environmental problems, however, the traditional analytical methods and test equipment for them are time-consuming and expensive. The electrochemical sensor using the non-covalent bond between graphene oxide (GO) and single-stranded tet (ss-tet) was established for specific tetracycline resistance genes (tet, composed of ss-tet and complementary ss-tet (ss-tet') in water) detection, which preparation time was only 35 min and far less than most reported sensors based on covalent bond. As the result of the detection for tet, the developed sensor not only had the low detection limit of 50.0 pM (8.1 × 102 copies·mL-1), the short detection time within 42 min, but also had satisfactory stability, excellent reproducibility, and highly selectivity (RSD < 4.43 %). Besides, it also had acceptable accuracy comparing to the real-time quantitative polymerase chain reaction (RT-qPCR) and PCR array in tet detection. Noticeably, it also had been successfully applied to tetA detection in different water samples. In brief, the prepared non-covalent bond sensor is simple, rapid, and suitable for highly selective and sensitive detection of the ARGs in actual water.

Nanomaterials-based aptasensors: An efficient detection tool for heavy-metal and metalloid ions in environmental and biological samples

In light of potential risks of heavy metal exposure, diverse aptasensors have been developed through the combination of aptamers with nanomaterials for the timely and efficient detection of metals in environmental and biological matrices. Aptamer-based sensors can benefit from multiple merits such as heightened sensitivity, facile production, uncomplicated operation, exceptional specificity, enhanced stability, low immunogenicity, and cost-effectiveness. This review highlights the detection capabilities of nanomaterial-based aptasensors for heavy-metal and metalloid ions based on their performance in terms of the basic quality assurance parameters (e.g., limit of detection, linear dynamic range, and response time). Out of covered studies, dendrimer/CdTe@CdS QDs-based ECL aptasensor was found as the most sensitive option with an LOD of 2.0 aM (atto-molar: 10-18 M) detection for Hg2+. The existing challenges in the nanomaterial-based aptasensors and their scientific solutions are also discussed.

Multiplex solid-phase RPA coupled CRISPR-based visual detection of SARS-CoV-2

The COVID-19 pandemic has presented a significant challenge to the world's public health and led to over 6.9 million deaths reported to date. A rapid, sensitive, and cost-effective point-of-care virus detection device is essential for the control and surveillance of the contagious severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic. The study presented here aimed to demonstrate a solid-phase isothermal recombinase polymerase amplification coupled CRISPR-based (spRPA-CRISPR) assay for on-chip multiplexed, sensitive and visual COVID-19 DNA detection. The assay targets the SARS-CoV-2 structure protein encoded genomes and can simultaneously detect two specific genes without cross-interaction. The amplified target sequences were immobilized on the one-pot device surface and detected using the mixed Cas12a-crRNA collateral cleavage of reporter-released fluorescent signal when specific genes were recognized. The endpoint signal can be directly visualized for rapid detection of COVID-19. The system was tested with samples of a broad range of concentrations (20 to 2 × 104 copies) and showed analytical sensitivity down to 20 copies per microliter. Furthermore, a low-cost blue LED flashlight (~$12) was used to provide a visible SARS-CoV-2 detection signal of the spRPA-CRISPR assay which could be purchased online easily. Thus, our platform provides a sensitive and easy-to-read multiplexed gene detection method that can specifically identify low concentration genes.

Film-forming, stable, conductive composites of polyhistidine/graphene oxide for electrochemical quantification of trace Pb2

Nanomaterials with unique properties, such as good film-formation and plentiful active atoms, play a vital role in the construction of electrochemical sensors. In this work, an in situ electrochemical synthesis of conductive polyhistidine (PHIS)/graphene oxide (GO) composite film (PHIS/GO) was designed to construct an electrochemical sensor for the sensitive detection of Pb²⁺. Herein, GO as an active material can directly form homogeneous and stable thin films on the electrode surface because of its excellent film-forming property. Then GO film was further functionalized by in situ electrochemical polymerization of histidine to obtain plentiful active atoms (N). Due to strong van der Waals forces between GO and PHIS, PHIS/GO film exhibited high stability. Furthermore, the electrical conductivity of PHIS/GO films was greatly improved by in situ electrochemical reduction technology and the plentiful active atoms (N) in PHIS are profitable for adsorbing Pb²⁺ from solution, tremendously enhancing the assay sensitivity. With the above unique property, the proposed electrochemical sensor showed high stability, a low detection limit (0.045 μg L^-1) and a wide linear range (0.1-300 μg L^-1) for the quantification of Pb²⁺. The method can also be extended to the synthesis of other film-forming nanomaterials to functionalize themselves and widen their potential applications, avoiding the addition of non-conductive film-forming substances.

Emerging Trends and Recent Progress of MXene as a Promising 2D Material for Point of Care (POC) Diagnostics

Two-dimensional (2D) nanomaterials with chemical and structural diversity have piqued the interest of the scientific community due to their superior photonic, mechanical, electrical, magnetic, and catalytic capabilities that distinguish them from their bulk counterparts. Among these 2D materials, two-dimensional (2D) transition metal carbides, carbonitrides, and nitrides with a general chemical formula of M_n+1X_nT_x (where n = 1-3), together known as MXenes, have gained tremendous popularity and demonstrated competitive performance in biosensing applications. In this review, we focus on the cutting-edge advances in MXene-related biomaterials, with a systematic summary on their design, synthesis, surface engineering approaches, unique properties, and biological properties. We particularly emphasize the property-activity-effect relationship of MXenes at the nano-bio interface. We also discuss the recent trends in the application of MXenes in accelerating the performance of conventional point of care (POC) devices towards more practical approaches as the next generation of POC tools. Finally, we explore in depth the existing problems, challenges, and potential for future improvement of MXene-based materials for POC testing, with the goal of facilitating their early realization of biological applications.

A novel ReS2–Nb2CTx composite as a sensing platform for ultrasensitive and selective electrochemical detection of dipyramidole from human serum

The electrochemical detection of dipyridamole (DIPY) is highly essential since it is extensively used for the treatment of cardiovascular diseases and to impart inhibitory effects for cancer patients. In this work, we report the development of a novel composite of MXene and ReS₂ (ReS₂–Nb₂CT_x) by hydrothermal method. It was found that Nb₂CT_x was partially oxidized and ReS₂ nanoparticles were distributed on the surface of Nb₂CT_x during the hydrothermal synthesis. The ReS₂–Nb₂CT_x was used to modify carbon cloth electrodes and used for the electrochemical detection of DIPY. The ratio of ReS₂ was optimized in the composite by varying the atomic ratio from 4 to 9 and it was found that 6ReS₂–Nb₂CT_x showed the best sensing characteristics owing to the optimum interaction between ReS₂ and Nb₂CT_x. The developed sensor was able to detect DIPY linearly in the range 100 pM–1 μM and achieved a limit of detection of (LOD) of 28 pM. The modified electrode exhibited excellent selectivity towards DIPY in the presence of other interferents in addition to its good storage stability and repeatability. Furthermore, the developed sensor was also used for the detection of DIPY in human serum samples. Thus, this work paves the way to develop MXene-based platform for fabrication of flexible device capable of monitoring the acute levels of DIPY.

MXene-Based Nucleic Acid Biosensors for Agricultural and Food Systems

MXene is a two-dimensional (2D) nanomaterial that exhibits several superior properties suitable for fabricating biosensors. Likewise, the nucleic acid (NA) in oligomerization forms possesses highly specific biorecognition ability and other features amenable to biosensing. Hence the combined use of MXene and NA is becoming increasingly common in biosensor design and development. In this review, MXene- and NA-based biosensors are discussed in terms of their sensing mechanisms and fabrication details. MXenes are introduced from their definition and synthesis process to their characterization followed by their use in NA-mediated biosensor fabrication. The emphasis is placed on the detection of various targets relevant to agricultural and food systems, including microbial pathogens, chemical toxicants, heavy metals, organic pollutants, etc. Finally, current challenges and future perspectives are presented with an eye toward the development of advanced biosensors with improved detection performance.

New Horizons for MXenes in Biosensing Applications

Over the last few decades, biosensors have made significant advances in detecting non-invasive biomarkers of disease-related body fluid substances with high sensitivity, high accuracy, low cost and ease in operation. Among various two-dimensional (2D) materials, MXenes have attracted widespread interest due to their unique surface properties, as well as mechanical, optical, electrical and biocompatible properties, and have been applied in various fields, particularly in the preparation of biosensors, which play a critical role. Here, we systematically introduce the application of MXenes in electrochemical, optical and other bioanalytical methods in recent years. Finally, we summarise and discuss problems in the field of biosensing and possible future directions of MXenes. We hope to provide an outlook on MXenes applications in biosensing and to stimulate broader interests and research in MXenes across different disciplines.