Tuning Electrocatalytic Aptitude by Incorporating α-MnO2 Nanorods in Cu-MOF/rGO/CuO Hybrids: Electrochemical Sensing of Resorcinol for Practical Applications

Multilayer Porous Fe/Co-N-MWCNT Electrocatalyst For Rechargeable Zinc-Air Batteries

The design of efficient, stable, low-cost non-precious metal-based electrocatalysts with enhanced oxygen reduction reaction (ORR) activity has garnered significant attention in the scientific community. This study introduces a novel electrocatalyst, Fe/Co-N-MWCNT, synthesized through the in-situ growth of ZIF-8 and Fe/Co-Phen on multi-walled carbon nanotubes (MWCNTs), followed by pyrolysis at varying temperatures to optimize its properties. The inclusion of Fe and Co during the pyrolysis process facilitated the creation of metal active sites and Fe-Co, enhancing electron transfer and ORR activity. Compared to Pt/C (E1/2=0.854 V, JL=4.90 mA cm-2), Fe/Co-N-MWCNT exhibited a similar half-wave potential (E1/2=0.812 V) and an improved limiting current density (JL=5.37 mA cm-2). Moreover, Fe/Co-N-MWCNT displayed remarkable stability, showing only a 7 mV negative shift in E1/2 after 2000 cycles. Ampere response testing indicated a current decay of only 7.8 % for Fe/Co-N-MWCNT after 10000 s, while Pt/C experienced a decay of about 18.4 %. The exceptional catalytic stability of Fe/Co-N-MWCNT positions it as a promising candidate for rechargeable zinc-air batteries, attributed to its high pyridinic nitrogen content, unique structure, and abundant metal active sites.

Efficient Electrochemical Sensing of Chlorpromazine with a Composite of Multiwalled Carbon Nanotubes and a Thiacalix[4]arene-Based Metal-Organic Framework

Chlorpromazine (CPMZ) is a representative drug for the treatment of psychiatric disorders. Excessive use of CPMZ could result in some serious health problems, and therefore, construction of a sensitive electrochemical sensor for CPMZ detection is greatly significant for human health. Herein, a feasible electrochemical method for the detection of CPMZ was provided. To design a suitable electrode surface modifier, a new two-dimensional (2D) thiacalix[4]arene-based metal-organic framework was designed and synthesized under solvothermal conditions, namely, [Co(TMPA)Cl2]MeOH·2EtOH·2H2O (Co-TMPA). Afterward, a series of composite materials was prepared by combining Co-TMPA with highly conductive carbon materials. Markedly, Co-TMPA/MWCNT-2@GCE (GCE = glassy carbon electrode, MWCNT = multiwalled carbon nanotube) exhibited the best electrocatalytic performance for CPMZ detection due to the synergistic effect between MWCNT and Co-TMPA. Particularly, it featured a low limit of detection (8 nM) and a wide linear range (0.05 to 1350 μM) in quantitative determination of CPMZ. Meanwhile, the sensor possessed excellent stability, selectivity, and reproducibility. Importantly, Co-TMPA/MWCNT-2@GCE was employed to analyze CPMZ in urine and serum with satisfactory recoveries (98.87-102.17%) and relative standard deviations (1.44-3.80%). Furthermore, the electrochemical detection accuracy of the Co-TMPA/MWCNT-2@GCE sensor was verified with the ultraviolet-visible spectroscopy technique. This work offers a promising sensor for the efficient analysis of drug molecules.

Facile design of FeCu metal-organic frameworks anchored on layer Ti3C2Tx MXene for high-performance electrochemical sensing of resorcinol

This work reports the rational design of a composite material by growing FeCu-MOF-919 on the surface of layered Ti3C2Tx MXene. The introduction of Ti3C2Tx MXene simultaneously weakens the aggregation of FeCu-MOF-919 and Ti3C2Tx MXene, which increases the electrochemical reaction active site of the composite material and improves the electrochemical activity. Interestingly, the FeCu-MOF-919/Ti3C2Tx based sensors were used to detect resorcinol (RS) with a wide linear range (0.5-152.5 μM), excellent sensitivity (0.23 μA μM-1 cm-2), low limit of detection (LOD = 0.08 μM) and outstanding stability. Meanwhile, the sensor shows high repeatability of 1.07 % RSD, reproducibility of 1.47 % RSD and anti-interference performance. What's more, the sensor can be successfully used to detect RS in tap water with good recoveries (96.25-103.37 %, RSD ≤2.18 %), demonstrating that the FeCu-MOF-919/Ti3C2Tx exhibits significant potential as an advanced sensing apparatus for the surveillance of RS in the natural environment.

Aptasensor based on gold nanostructure-decorated 2D Cu metal-organic framework nanosheets for highly sensitive and specific electrochemical lipopolysaccharide detection

Detecting lipopolysaccharide (LPS) using electrochemical methods is significant because of their exceptional sensitivity, simplicity, and user-friendliness. Two-dimensional metal-organic framework (2D-MOF) that merges the benefits of MOF and 2D nanostructure has exhibited remarkable performance in constructing electrochemical sensors, notably surpassing traditional 3D-MOFs. In this study, Cu[tetrakis(4-carboxylphenyl)porphyrin] (Cu-TCPP) and Cu(tetrahydroxyquinone) (Cu-THQ) 2D nanosheets were synthesized and applied on a glassy carbon electrode (GCE). The 2D-MOF nanosheets, which serve as supporting layers, exhibit improved electron transfer and electronic conductivity characteristics. Subsequently, the modified electrode was subjected to electrodeposition with Au nanostructures, resulting in the formation of Au/Cu-TCPP/GCE and Au/Cu-THQ/GCE. Notably, the Au/Cu-THQ/GCE demonstrated superior electrochemical activity because of the 2D morphology, redox ligand, dense Cu sites, and improved deposition of flower-like Au nanostructure based on Cu-THQ. The electron transfer specific surface area was increased by the improved deposition of Au nanostructures, which facilitates enriched binding of LPS aptamer and significantly improved the detection performance of Apt/Au/Cu-THQ/GCE electrochemical aptasensor. The limit of detection for LPS reached 0.15 fg/mL with a linear range of 1 fg/mL - 100 pg/mL. The proposed aptasensor demonstrated the ability to detect LPS in serum samples with satisfactory accuracy, indicating significant potential for clinical diagnosis.

Electrochemical DNA-nano biosensor for the detection of Goserelin as anticancer drug using modified pencil graphite electrode

Goserelin is an effective anticancer drug, but naturally causes several side effects. Hence the determination of this drug in biological samples, plays a key role in evaluating its effects and side effects. The current studies have concentrated on monitoring Goserelin using an easy and quick DNA biosensor for the first time. In this study, copper(II) oxide nanoparticles were created upon the surface of multiwalled carbon nanotubes (CuO/MWCNTs) as a conducting mediator. The modified pencil graphite electrode (ds-DNA/PA/CuO/MWCNTs/PGE) has been modified with the help of polyaniline (PA), ds-DNA, and CuO/MWCNTs nanocomposite. Additionally, the issue with the bio-electroanalytical guanine oxidation signal in relation to ds-DNA at the surface of PA/CuO/MWCNTs/PGE has been examined to determination Goserelin for the first time. It also, established a strong conductive condition to determination Goserelin in nanomolar concentration. Thus, Goserelin's determining, however, has a 0.21 nM detection limit and a 1.0 nM-110.0 µM linear dynamic range according to differential pulse voltammograms (DPV) of ds-DNA/PA/CuO/MWCNTs/PGE. Furthermore, the molecular docking investigation highlighted that Goserelin is able to bind ds-DNA preferentially and supported the findings of the experiments. The determining of Goserelin in real samples has been effectively accomplished in the last phase using ds-DNA/PA/CuO/MWCNTs/PGE.

Unlocking the future of brain research: MOFs, TMOs, and MOFs/TMOs for electrochemical NTMs detection and analysis

The central nervous system relies heavily on neurotransmitters (NTMs), and NTM imbalances have been linked to a wide range of neurological conditions. Thus, the development of reliable detection techniques is essential for advancing brain studies. This review offers a comprehensive analysis of metal-organic frameworks (MOFs), transition metal oxides (TMOs), and MOFs-derived TMOs (MOFs/TMOs) as materials for electrochemical (EC) sensors targeting the detection of key NTMs, specifically dopamine (DA), epinephrine (EP), and serotonin (SR). The unique properties and diverse families of MOFs and TMOs, along with their nanostructured hybrids, are discussed in the context of EC sensing. The review also addresses the challenges in detecting NTMs and proposes a systematic approach to tackle these obstacles. Despite the vast amount of research on MOFs and TMOs-based EC sensors for DA detection, the review highlights the gaps in the literature for MOFs/TMOs-based EC sensors specifically for EP and SR detection, as well as the limited research on microneedles (MNs)-based EC sensors modified with MOFs, TMOs, and MOFs/TMOs for NTMs detection. This review serves as a foundation to encourage researchers to further explore the potential applications of MOFs, TMOs, and MOFs/TMOs-based EC sensors in the context of neurological disorders and other health conditions related to NTMs imbalances.

An ultrasensitive ratiometric electrochemical aptasensor based on metal-organic frameworks and nanoflower-like Bi2CuO4 for human epidermal growth factor receptor 2 detection

An ultra-sensitive ratiometric electrochemical aptasensor was constructed based on metal-organic frameworks (MOFs) and bimetallic oxides for the detection of the human epidermal growth factor receptor 2 (HER2), a breast cancer marker. The aluminum metal-organic framework (Al-MOF) and cerium-metal-organic framework (Ce-MOF) have higher specific surface area, which is conducive to load more aptamers or complementary DNA (cDNA), and realize the amplification of internal reference signal Fc. Furthermore, nanoflower-like bismuth copper oxide (Bi2CuO4) with abundant active sites was introduced to modify more aptamers on its surface, which were then fixed to the glassy carbon electrode (GCE) to amplify the detection signal. The quantitative detection of HER2 was achieved by differential pulse voltammetry (DPV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The materials were characterized by scanning electron microscope, transmission electron microscope, Zeta potential analyzer, X-ray diffraction and X-ray photoelectron spectroscopy. The ratiometric electrochemical aptasensor based on nanomaterial and chain displacement signal amplification technology could discern HER2 in a very wide range (0.001-20.0 ng/mL) with an extremely low detection limit (0.049 pg/mL) and has demonstrated good performance in clinical serum analysis. This strategy also provides a feasible idea for sensitive analysis of other clinical tumor markers.

A Study on the O2 Plasma Etching Method of Spray-Formed SWCNT Films and Their Utilization as Electrodes for Electrochemical Sensors

In this study, we analyzed the morphological changes and molecular structure changes on the surface of single-walled carbon nanotube (SWCNT) films during oxygen plasma (O2) etching of SWCNT surfaces formed by the spray method and analyzed their potential use as electrochemical electrodes. For this purpose, a SWCNT film was formed on the surface of a glass substrate using a self-made spray device using SWCNT powder prepared with DCB as a solvent, and SEM, AFM, and XPS analyses were performed as the SWCNT film was O2 plasma etched. SEM images and AFM measurements showed that the SWCNT film started etching after about 30 s under 50 W of O2 plasma irradiation and was completely etched after about 300 s. XPS analysis showed that as the O2 plasma etching of the SWCNT film progressed, the sp2 bonds representing the basic components of graphite decreased, the sp3 bonds representing defects increased, and the C-O, C=O, and COO peaks increased simultaneously. This result indicates that the SWCNT film was etched by the O2 plasma along with the oxygen species. In addition, electrochemical methods were used to verify the damage potential of the remaining SWCNTs after O2 plasma etching, including cyclic voltammetry, Randles plots, and EIS measurements. This resulted in a reversible response based on perfect diffusion control in the cyclic voltammetry, and an ideal linear curve in the Randles plot of the peak current versus square root scan rate curve. EIS measurements also confirmed that the charge transfer resistance of the remaining SWCNTs after O2 plasma etching is almost the same as before etching. These results indicate that the remaining SWCNTs after O2 plasma etching do not lose their unique electrochemical properties and can be utilized as electrodes for biosensors and electrochemical sensors. Our experimental results also indicate that the ionic conductivity enhancement by O2 plasma can be achieved additionally.

A Facile Preparation of Sandwich-Structured Pd/Polypyrrole-Graphene/Pd Catalysts for Formic Acid Electro-Oxidation

Direct formic acid fuel cells (DFAFCs) are one of the most promising power sources due to its high conversion efficiency; relatively low carbon emissions, toxicity, and flammability; convenience; and low-cost storage and transportation. However, the key challenge to large-scale commercial applications is its poor power performance and the catalyst's high preparation cost. In this study, a new sandwich-structured Pd/polypyrrole-graphene/Pd (Pd/PPy-Gns/Pd)-modified glassy carbon electrode (GCE) was prepared using a simple constant potential (CP) electrodeposition technique. On the basis of the unique synthetic procedure and structural advantages, the Pd/PPy-Gns/Pd shows a fast charge/mass transport rate, high electrocatalytic activity, and great stability for formic acid electro-oxidation (FAO). The mass activity of Pd/PPy-Gns/Pd electrode reaches 917 mA·mg^-1_Pd. The excellent catalytic activity is mainly due to the uniform embedding of Pd nanoparticles on the polypyrrole-graphene (PPy-Gns) support, which exposes more active sites, and prevents the shedding and inactivation of Pd nanoparticles. At the same time, the introduction of graphene (Gns) in the PPy further improved the conductivity of the catalyst and accelerated the transfer of electrons.

MOFs-based Fe@YAU-101/GCE electrochemical sensor platform for highly selective detecting trace multiplex heavy metal ions

The construction of sensors with specific recognition functions can easily, sensitively and efficiently detect heavy metal ions, which is a demand in the field of electrochemical sensing and an important topic in the detection of environmental pollutants. An electrochemical sensor based on MOFs composites was developed for sensing of multiplex metal ions. The large surface area, adjustable porosities and channels in MOFs facilitate successful loading of sufficient quantities highly active units. The active units and pore structures of MOFs are regulated and synergetic with each other to enhance the electrochemical activity of MOFs composites. Thus, the selectivity, sensitivity and reproducibility of MOFs composites have been improved. Fortunately, after characterization, Fe@YAU-101/GCE sensor with strong signal was successfully constructed. In the presence of target metal ions in solution, the Fe@YAU-101/GCE can efficiently and synchronously identify Hg²⁺, Pb²⁺, and Cd²⁺. The detection limits (LOD) are 6.67 × 10^-10 M(Cd²⁺), 3.33 × 10^-10 M(Pb²⁺) and 1.33 × 10^-8 M (Hg²⁺), and are superior to the permissible limits set by the National Environmental Protection Agency. The electrochemical sensor is simple without sophisticated instrumentation and testing processes, hence promising for practical applications.

Efficient removal of bovine serum albumin from water by cellulose acetate membranes modified with clay and titania nano particles

Modified cellulose acetate membranes with bentonite clay (CA/bent) and TiO₂ nanoparticles (CA/TiO₂) using the phase inversion method are successfully prepared and characterized. These Membranes are favored due to their high salt rejection properties and recyclability. The IR and EDX spectral data indicate the formation of modified membranes. The Scan Electron Microscope micrographs show that the modified membranes have smaller particle sizes with higher porosity than the neat membrane. The average pore diameter is 0.31 µm for neat cellulose acetate membrane (CA) and decreases to 0.1 µm for CA/0.05bent. All modified membranes exhibit tensile strengths and elongation percentages more than the neat membrane. The higher tensile strength and the maximum elongation% are 15.3 N/cm² and 11.78%, respectively, for CA/0.05bent. The thermogravimetric analysis of modified membranes shows higher thermal stability than the neat membrane. The modified membranes exhibit enhanced wettability and hydrophilicity compared with cellulose acetate, by measuring the contact angle which decreases from 60° (CA) to 40° (CA/0.1bent). The ultrafiltration tests indicated that the CA/bent and CA/TiO₂ are better than CA. The most efficient nanocomposite membrane is CA/0.05bent with 100% removal of (BSA) from industrial water with a flux equal to 9.5 mL/min under an applied pressure of 20 bar. Thus, this study introduces a novel ultrafiltration membrane (CA/0.05bent) that can be used effectively to completely remove bovine serum albumin from contaminated water.

Development of the DNA-based voltammetric biosensor for detection of vincristine as anticancer drug

In the article presented herein, a deoxyribonucleic acid (DNA) biosensor is introduced for Vincristine determination in pharmaceutical preparations based on the modification of screen printed electrode (SPE) with double-stranded DNA (ds-DNA), polypyrrole (PP), peony-like CuO:Tb³⁺ nanostructure (P-L CuO:Tb³⁺ NS). The developed sensor indicated a wide linear response to Vincristine concentration ranged from 1.0 nM to 400.0 μM with a limit of detection as low as .21 nM. The intercalation of Vincristine with DNA guanine led to the response. The optimized parameters for the biosensor performance were ds-DNA/Vincristine interaction time, DNA concentration and type of buffer solution. The docking investigation confirm the minor groove interaction between guanine base at surface of or ds-DNA/PP/P-L CuO:Tb³⁺ NS/SPE and Vincristine. The proposed sensor could successfully determine Vincristine in Vincristine injections and biological fluids, with acceptable obtains.

The Roadmap of Graphene-Based Sensors: Electrochemical Methods for Bioanalytical Applications

Graphene (GR) has engrossed immense research attention as an emerging carbon material owing to its enthralling electrochemical (EC) and physical properties. Herein, we debate the role of GR-based nanomaterials (NMs) in refining EC sensing performance toward bioanalytes detection. Following the introduction, we briefly discuss the GR fabrication, properties, application as electrode materials, the principle of EC sensing system, and the importance of bioanalytes detection in early disease diagnosis. Along with the brief description of GR-derivatives, simulation, and doping, classification of GR-based EC sensors such as cancer biomarkers, neurotransmitters, DNA sensors, immunosensors, and various other bioanalytes detection is provided. The working mechanism of topical GR-based EC sensors, advantages, and real-time analysis of these along with details of analytical merit of figures for EC sensors are discussed. Last, we have concluded the review by providing some suggestions to overcome the existing downsides of GR-based sensors and future outlook. The advancement of electrochemistry, nanotechnology, and point-of-care (POC) devices could offer the next generation of precise, sensitive, and reliable EC sensors.

Engineering MOFs derived metal oxide nanohybrids: Towards electrochemical sensing of catechol in tea samples

In this work, we have successfully developed Cu-MOF/CuO/NiO nanocomposites (NCs) and employed as a novel electrochemical sensing platform in catechol (CC) detection. The Scanning electron microscopy (SEM) along Energy dispersive X-ray Analysis (EDX), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) are carried out to characterize the as-fabricated Cu-MOF/CuO/NiO NCs. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques have used to obtain oxidation peak currents of CC. Glassy carbon electrode (GCE) modified with Cu-MOF/CuO/NiO has exposed the superb EC properties representing low limit of detection (LOD) of 0.0078 µM (S/N = 3). To assess the practicability of Cu-MOF/CuO/NiO based sensing medium, it has been used to detect CC from two varieties of tea, namely black and green. Thus, we anticipate that this structural integration strategy possesses encouraging application potential in sensing podium and material synthesis.

Electrochemical aptasensor based on the target-induced strand displacement strategy-driven for T-2 toxin detection

Herein, an aptasensor based on target-induced strand displacement (TISD) strategy was developed for sensitive detection of T-2 toxin. Gold nanoparticles@ aminated manganese dioxide (AuNPs@NH₂-MnO₂) exhibited excellent electrical conductivity and provided more binding sites for aptamer (Apt). Besides, polyethyleneimine-reduced graphene oxide/gold‑platinum core-shell nanorods composites (PEI-rGO/Pt@Au NRs) were used to be carriers for signaling tags, as their sufficiently large specific surface area improved the loading capacity for signal molecules. In the presence of T-2, the Apt sequence was more inclined to form an Apt-T-2 complex, and the cDNA was displaced from the Apt-cDNA duplex, while the signal tag was released, resulting in a weakened MB signal, differential pulse voltammetry (DPV) was used to record the signal change. Under optimal conditions, the signal response of the constructed electrochemical aptasensor exhibited a good linear relationship with the concentration of T-2. The detection limit was 8.74 × 10^-7 ng mL^-1over a wide range of concentration from 5 × 10^-6 ng mL^-1 to 5 ng mL^-1. Furthermore, the proposed aptasensor had excellent specificity, good stability and can be well applied to the detection of real samples. It provided a new avenue for the research and development of sensitive aptasensors in food detection and analysis.

Recent advances in metal-based nanoporous materials for sensing environmentally-related biomolecules

Highly sensitive, stable, selective, efficient, and short reaction time sensors play a substantial role in daily life/industry and are the need of the day. Due to the rising environmental issues, nanoporous carbon and metal-based materials have attracted significant attention in environmental analysis owing to their intriguing and multifunctional properties and cost-effective and rapid detection of different analytes by sensing applications. Environmental-related issues such as pollution have been a significant threat to the world. Therefore, it is necessary to fabricate highly promising performance-based sensor materials with excellent reliability, selectivity and good sensitivity for monitoring various analytes. In this regard, different methods have been employed to fabricate these sensors comprising metal, metal oxides, metal oxide carbon composites and MOFs leading to the formation of nanoporous metal and carbon composites. These composites have exceptional properties such as large surface area, distinctive porosity, and high conductivity, making them promising candidates for several versatile sensing applications. This review covers recent advances and significant studies in the sensing field of various nanoporous metal and carbon composites. Key challenges and future opportunities in this exciting field are also part of this review.

A reagentless electrochemical immunosensor for sensitive detection of carcinoembryonic antigen based on the interface with redox probe-modified electron transfer wires and effectively immobilized antibody

Convenient and sensitive detection of tumors marked in serum samples is of great significance for the early diagnosis of cancers. Facile fabrication of reagentless electrochemical immunosensor with efficient sensing interface and high sensitivity is still a challenge. Herein, an electrochemical immunosensor was easily fabricated based on the easy fabrication of immunoassay interface with electron transfer wires, confined redox probes, and conveniently immobilized antibodies, which can achieve sensitive and reagentless determination of the tumor marker, carcinoembryonic antigen (CEA). Carboxyl multi-walled carbon nanotubes (MWCNTs) were firstly modified with an electrochemical redox probe, methylene blue (MB), which has redox potentials distinguished from those of redox molecules commonly existing in biological samples (for example, ascorbic acid and uric acid). After the as-prepared MB-modified MWCNT (MWCNT-MB) was coated on the supporting glassy carbon electrode (GCE), the MWCNT-MB/GCE exhibited improved active area and electron transfer property. Polydopamine (PDA) was then in situ synthesized through simple self-polymerization of dopamine, which acts as the bio-linker to covalently immobilize the anti-CEA antibody (Ab). The developed immunosensor could be applied for electrochemical detection of CEA based on the decrease in the redox signal of MB after specific binding of CEA and immobilized Ab. The fabricated immunosensor can achieve sensitive determination of CEA ranging from 10 pg/ml to 100 ng/ml with a limit of detection (LOD) of 0.6 pg/ml. Determination of CEA in human serum samples was also realized with high accuracy.

Carbon-supported X-manganate (XNi, Zn, and Cu) nanocomposites for sensitive electrochemical detection of trace heavy metal ions

Heavy metal ion pollution has always been a stringent problem facing the global environment. Therefore, the detection of heavy metal ions has been extremely important and challenging. An efficient and simple method for the preparation of carbon-supported X-manganate (XNi, Zn, and Cu) nanocomposites was explored for the individual and simultaneous electrochemical detection of Pb(II) and Hg(II). The metallic salt solutions were mixed with graphene to form the precursors through a hydrothermal reaction, and calcined in the air to obtain the final products. The structure and morphology of the synthesized NiMn₂O₄-graphene (NMO-GR), ZnMn₂O₄-graphene (ZMO-GR), and CuMn₂O₄-graphene (CMO-GR) nanocomposites were characterized by various methods, and NMO-GR showed more excellent electrochemical performances by square wave anodic stripping voltammetry (SWASV) than ZMO-GR and CMO-GR. NMO-GR provided a large specific surface area, abundant reaction sites, and good electrical conductivity, thereby enhancing its electrochemical performance. The electrochemical sensor based on NMO-GR displayed the widest linear ranges (1.4-7.7 μM for Pb(II) and 0.7-6.7 μM for Hg(II)) and with the lowest detection limits (0.050 μM for Pb(II) and 0.027 μM for Hg(II)) than ZMO-GR and CMO-GR. This study offered a new way to simultaneously detect Pb(II) and Hg(II), and greatly expanded its application in the field of electrochemistry.

Tuning the Redox Chemistry of Copper Oxide Nanoarchitectures Integrated with rGOP via Facet Engineering: Sensing H2S toward SRB Detection

The ultrasensitive determination of sulfate reducing bacteria (SRB) is of great significance for their crucial roles in environmental and industrial harms together with the early detection of microbial corrosion. In this work, we report the development of highly efficient electrocatalysts, i.e., Cu₂O-CuO extended hexapods (EHPs), which are wrapped on homemade freestanding graphene paper to construct a flexible paper electrode in the electrochemical sensing of the biomarker sulfide for SRB detection. Herein Cu₂O-CuO EHPs have been synthesized via a highly controllable and facile approach at room temperature, where the redox centers of copper oxide nanoarchitectures are tuned via facet engineering, and then they are deposited on the graphene paper surface through an electrostatic adsorption to enable homogeneous and highly dense distribution. Owing to the synergistic contribution of high electrocatalytic activity from the Cu mixed oxidation states and abundant catalytically active facets of Cu₂O-CuO EHPs and high electrical conductivity of the graphene paper electrode substrate, the resultant nanohybrid paper electrode has exhibited superb electrochemical sensing properties for H₂S with a wide linear range up to 352 μM and an extremely low detection limit (LOD) of 0.1 nM with a signal-to-noise ratio of 3 (S/N = 3), as well as high sensitivity, stability, and selectivity. Furthermore, taking advantage of the good biocompatibility and mechanical flexibility, the electrochemical sensing platform based on the proposed electrode has been applied in the sensitive detection of SRB in environmental samples through the sensing of sulfide from SRB, which holds great promise for on-site and online corrosion and environmental monitoring.

Advancing interfacial properties of carbon cloth via anodic-induced self-assembly of MOFs film integrated with α-MnO2: A sustainable electrocatalyst sensing acetylcholine

The metal organic frameworks (MOFs) with tunable composition, modified structure, and morphologically controlled nanoarchitectures are quite imperative to improve the electrochemical (EC) performances of sensing platforms. Herein, EC control over the fabrication of HKUST-1 (Cu-MOFs) nanocrystals is achieved via anodic-induced electrodeposition approach following the mixing of Cu²⁺ salt precursor in the vicinity of benzene-1,3,5-tricarboxylate (BTC^3-) ligands. The problem of controlled mass transfer and slow dispersal of MOFs is resolved by EC deposition of pyramidal-octagonal MOFs on a highly conductive and flexible carbon substrate (activated carbon cloth, ACC) wrapped with rGO layers (ACC-rGO@Cu(BTC). Further, α-MnO₂ is integrated on ACC-rGO@Cu(BTC) to achieve the synergistic effect of ternary structure interfaces. The novel ACC-rGO@Cu(BTC)@MnO₂ based flexible electrode exhibits striking EC performance toward non-enzymatic sensing of acetylcholine (ACh) including wide linear range (0.1 µM - 3 mM), lowest detection limit (5 nM, S/N = 3), high selectivity, and long-term stability. Moreover, the developed sensing system has been applied for real-time detection of ACh efflux released from three different cell lines and biological matrices. Our work unlocks a new prospect of precisely structured MOFs with extensive functionalities and scaled-up fabrication methods via selection of nanoscale reaction centers to develop flexible sensing devices.

Metal Centers and Organic Ligands Determine Electrochemistry of Metal-Organic Frameworks

The properties and applications of metal-organic frameworks (MOFs) can be tuned by their metal centers and organic ligands. To reveal experimentally and theoretically the influence of metal centers and ligands on electrochemical performance of MOFs, three MOFs with copper or zinc centers and organic ligands of 2-methylimidazole (2MI) or 1,3,5-benzenetricarboxylic acid (H₃ BTC) are synthesized and characterized in this study. 2D and porous Cu-2MI exhibits a larger active area, faster electron transfer capability, and stronger adsorption capacity than bulk Cu-BTC and dodecahedron Zn-2MI. Density functional theory calculations of adsorption ability of three MOFs toward xanthine (XA), hypoxanthine (HXA), and malachite green (MG) prove that 2D Cu-2MI has the strongest adsorption energies to three targets. Rotating disk electrode measurements reveal that 2D Cu-2MI features the biggest intrinsic heterogeneous rate constant toward three analytes. On 2D Cu-2MI sensitive and selective monitoring of XA, HXA, and MG is then achieved using differential pulse voltammetry. Their monitoring in real samples on 2D Cu-2MI is accurate and comparable with that using high-performance liquid chromatography. In summary, regulation of electrochemical sensing features of MOFs is realized through defining selected metal centers and organic ligands.

Extension of duplex specific nuclease sensing application with RNA aptamer

Duplex specific nuclease (DSN) that can precisely cleave DNA portion in double-stranded DNA or DNA-RNA hybrid has engrossed immense attention owing to its great potential in emerging bioanalytical applications. Here, we present a novel approach to extend DSN sensing application by coupling RNA aptamer. Specially designed RNA ligand sequences are used to capture the target and simultaneously provide complementary sequences of DNA for DSN aided fluorescent signal enhancement. A clotting enzyme, thrombin, has been used as a model analyte. One RNA aptamer combined with the target molecule can generate fluorescent signals through cleavage of hybridized TaqMan DNA probe (P2) by DSN. The proposed assay has achieved the lowest detection limit of 0.039 pM. The assay has been applied for real-time detection of thrombin release from live cells and other biotic media for early disease diagnosis. The developed method is versatile and can detect various other targets by choosing the relevant aptamer and probe sequences. This method is promising to be applied to medical diagnosis, biosensing, food safety, environmental monitoring, and other fields.

Fluorescent Copper Nanomaterials for Sensing NO2− and Temperature

In this work, highly fluorescent copper nanomaterials were synthesized by using ascorbic acid as a ligand. The excitation wavelength of copper nanomaterials is 367 nm, and the emission wavelength is 420 nm. The size range is 5–6 nm. Nitrite can selectively quench the fluorescence of copper nanomaterials. Therefore, copper nanomaterials can be used to selectively detect nitrite ions. The linear equation is F = −32.94 c (NO₂⁻) + 8,455, and the correlation coefficient is 0.9435. At the same time, we found that the fluorescence intensity of copper nanomaterials has a good correlation with temperature (20–60°C), which shows that they have great potential in the application of nanothermometers.

Boosting electrocatalytic activity of carbon fiber@fusiform-like copper-nickel LDHs: Sensing of nitrate as biomarker for NOB detection

Morphological evolution of layered double hydroxides (LDHs) with preferential crystal facets has appealed gigantic attention of research community. Herein, we prepare hierarchical hybrid material by structurally integrating fusiform-like CuNiAl LDHs petals on conductive backbone of CF (CF@CuNiAl LDHs) and investigate electrocatalytic behavior in nitrate reduction over a potential window of -0.7 V to +0.7 V. The CF@CuNiAl LDHs electrode exhibits remarkable electrocatalytic aptitude in nitrate sensing including broad linear ranges of 5 nM to 40 µM and 75 µM to 2.4 mM with lowest detection limit of 0.02 nM (S/N = 3). The sensor shows sensitivity of 830.5 ± 1.84 µA mM^1- cm^2- and response time within 3 s. Owing to synergistic collaboration of improved electron transfer kinetics, specific fusiform-like morphology, presence of more catalytically active {111} facets and superb catalytic activity of LDHs, CF@CuNiAl LDHs electrode has outperformed as electrochemical sensor. Encouraged from incredible performance, CF@CuNiAl LDHs flexible electrode has been applied in real-time in-vitro detection of nitrite oxidizing bacteria (NOB) through the sensing of nitrate because NOB convert nitrite into nitrate by characteristic metabolic process to obtain their energy. Further, CF@CuNiAl LDHs based sensing podium has also been employed in in-vitro detection of nitrates from mineral water, tap water and Pepsi drink.

A Simple Colorimetric Assay for Sensitive Cu2+ Detection Based on the Glutathione-Mediated Etching of MnO2 Nanosheets

In this paper, we developed a quick, economical and sensitive colorimetric strategy for copper ions (Cu²⁺) quantification via the redox response of MnO₂ nanosheets with glutathione (GSH). This reaction consumed MnO₂ nanosheets, which acted as a catalyst for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product (oxTMB). In the presence of Cu²⁺, the GSH was catalyzed to GSSG (oxidized glutathione), and the solution changed from colorless to deep blue. Under the optimum conditions, the absorption signal of the oxidized product (oxTMB) became proportional to Cu²⁺ concentration in the range from 10 to 300 nM with a detection limit of 6.9 nM. This detection system showed high specificity for Cu²⁺. Moreover, the system has been efficaciously implemented for Cu²⁺ detection in actual tap water samples. The layered-nanostructures of MnO₂ nanosheets make it possess high chemical and thermal stability. TMB can be quickly oxidized within 10 min by the catalyzing of MnO₂ nanosheets with high oxidase-like activity. There is no need of expensive reagents, additional H₂O₂ and complicated modification processes during the colorimetric assay. Therefore, the strategy primarily based on MnO₂ nanosheets is promising for real-time, rapid and highly sensitive detection of Cu²⁺ under practical conditions.

Self-driven in situ facile synthesis of CuO/Cu2O for enhanced catalytic reduction of 4-nitrophenol by acetic acid

A series of CuO, Cu2O and CuO/Cu2O catalyst structures with different morphologies are synthesized in situ by controlling the anionic species of the copper salts in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP).

Advances in Metal-organic Frameworks (MOFs) based Biosensors for Diagnosis: An Update

Metal-organic frameworks (MOFs) have significant advantages over other candidate classes of chemo-sensory materials owing to their extraordinary structural tunability and characteristics. MOF-based biosensing is a simple and convenient method for identifying various species. Biomarkers are molecular or cellular processes that link environmental exposure to a health outcome. Biomarkers are important in understanding the links between environmental chemical exposure and the development of chronic diseases, as well as in identifying disease-prone subgroups. Until now, several species, including nanoparticles (NPs) and their nanocomposites, small molecules, and unique complex systems, have been used for the chemical sensing of biomarkers. Following the overview of the field, we discussed the various fabrication methods for MOFs development in this review. We provide a thorough overview of the previous five years of progress to broaden the scope of analytes for future research. Several enzymatic and non-enzymatic sensors are offered, together with a mandatory measuring method that includes detection range and dynamic range. In addition, we reviewed the comparison of enzymatic and non-enzymatic biosensors, inventive edges, and the difficulties that need to be solved. This work might open up new possibilities for material production, sensor development, medical diagnostics, and other sensing fields.

Construction of bimetallic FeCo–SA/DABCO nanosheets by modulating the electronic structure for improved electrocatalytic oxygen evolution

For energy conversion and storage, the electrochemical oxygen evolution process (OER) is the crucial half-reaction process.

Specific sensing of resorcin based on the hierarchical porous nanoprobes constructed by cuttlefish-derived biomaterials through differential pulse voltammetry

The specific detection of resorcin from its isomers is a current research hotspot. Thus in our work, a ternary hierarchical porous nanoprobe has been constructed based on the combination of cuttlefish ink and bimetallic Au@Ag nanoclusters for the specific sensing of resorcin. Briefly, through electrostatic interaction, Au@Ag core-shell nanoclusters are immobilized on the surface of polydopamine extracted from cuttlefish, which is turned into nitrogen-doped porous carbon functionalized by bimetallic Au@Ag by topological transformation subsequently. Afterward, an electrochemical sensor is fabricated based on the nanoprobes for specifically determining resorcin in solution by differential pulse voltammetry, and the linear detection ranges of the sensor are 1-100 μM and 1.2-4 mM while the detection limit reaches 0.06 μM. Meanwhile, the sensing mechanism of resorcin by the pre-fabricated sensor is detailedly studied by density functional theory to obtain a clear electrochemical process. Besides, the selectivity, stability, plus reproducibility of the pre-fabricated sensor have been also tested, and the determinations for resorcin in real environmental water samples have also been performed with good recoveries, revealing the auspicious application potential in the environmental monitoring.

Tin derived antimony/nitrogen-doped porous carbon (Sb/NPC) composite for electrochemical sensing of albumin from hepatocellular carcinoma patients

An electrochemical sensor based on an antimony/nitrogen-doped porous carbon (Sb/NPC) composite has been developed for the quantitative detection of albumin from hepatocellular carcinoma (HCC) patients. Sb/NPC is hydrothermally synthesized from Sn/NPC precursors. The synthesized precursor (Sn/NPC) and the product (Sb/NPC) are characterized by XRD, FTIR, TGA, UV/Vis, SEM, and AFM. Cyclic voltammetry, chronoamperometry, and electrochemical impedance studies are used to investigate the electrochemical performance of Sb/NPC-GCE. Sb/NPC-GCE detects albumin at physiological pH of 7.4 in the potential range 0.92 V and 0.09 V for oxidation and reduction, respectively. LOD and recovery of Sb/NPC-GCE for the determination of albumin are 0.13 ng.mL^-1 and 66.6 ± 0.97-100 ± 2.73%, respectively. Chronoamperometry of the modified working electrode demonstrates its stability for 14 h, indicating its reusability and reproducibility. Sb/NPC-GCE is a selective sensor for albumin detection in the presence of interfering species. The electrode has been applied for albumin detection in human serum samples of HCC patients. A negative correlation of albumin with alpha-fetoprotein levels in HCC patients is observed by statistical analysis.