Rapid microcystin-LR detection using antibody-based electrochemical biosensors with a simplified calibration curve approach

Harmful algal blooms (HABs) can release cyanotoxins such as microcystins (MCs), especially, microcystin-leucine-arginine (MC-LR) which is one of the commonest and most toxic, into our water bodies and can lead to several acute or chronic diseases such as liver diseases and respiratory irritation in humans. There is an increasing need for rapid and simple detection of MC-LR in water bodies for early warning of HABs. In this study, we developed an innovative on-site screening electrochemical impedance spectroscopy (EIS) biosensor with a simplified calibration curve that can rapidly detect blooms for early action in similar water bodies. The novel aspect of this research is that various chemical cleaning procedures and surface modifications were evaluated to improve the antibody-embedded electrochemical sensor performance. In addition, a simplified calibration curve was constructed from different water samples to reduce the need for frequent recalibration in practical applications. In this study, two distinct commercially available screen-printed carbon electrodes (SPCEs) were modified as a cost-effective substrate for MC-LR biosensing with anti-MC-LR/MC-LR/cysteamine-coating. The study showed that an appropriate cleaning procedure might minimize the sensor performance difference after each electrode modification. The biosensor showed excellent sensitivity toward MC-LR detection in lake water samples with a limit of detection (LOD) of 0.34 ngL-1. The simplified calibration curve was developed and used to predict unknown MC-LR concentrations in several lake water samples with a relative standard deviation (RSD) of 1.0-4.4% and a recovery of 75-112%, indicating the suitability of the developed biosensor and a streamlined calibration curve for rapid MC-LR measurements for different water bodies with similar water quality. This approach can therefore reduce the need for frequent calibration efforts and can be employed as the first line of testing for MC-LR in drinking and recreational water sources, especially in emergencies.

Optimizing graphene content in scaffolds for evenly distributed crumpled MoS2paper wads as anodes for high-performance Li-ion batteries

Lithium-ion batteries (LIBs) have revolutionized portable electronics, yet their conventional graphite anodes face capacity limitations. Integrating graphene and 3D molybdenum disulfide (MoS2) offers a promising solution. Ensuring a uniform distribution of 3D MoS2nanostructures within a graphene matrix is crucial for optimizing battery performance and preventing issues like agglomeration and capacity degradation. This study focuses on synthesizing a uniformly distributed paper wad structure by optimizing a composite of reduced graphene oxide RGO@MoS2through structural and morphological analyses. Three composites with varying graphene content were synthesized, revealing that the optimized sample containing 30 mg RGO demonstrates beneficial synergy between MoS2and RGO. The interconnected RGO network enhances reactivity and conductivity, addressing MoS2aggregation. Experimental results exhibit an initially superior capacity of 911 mAh g-1, retained at 851 mAh g-1even after 100 cycles at 0.1 A g-1current density, showcasing improved rate efficiency and long-term stability. This research underscores the pivotal role of graphene content in customizing RGO@MoS2composites for enhanced LIB performance.

2D Hybrid Nanocomposite Materials (h-BN/G/MoS2) as a High-Performance Supercapacitor Electrode

The nanocomposites of hexagonal boron nitride, molybdenum disulfide, and graphene (h-BN/G/MoS2) are promising energy storage materials. The originality of the current work is the first-ever synthesis of 2D-layered ternary nanocomposites of boron nitrate, graphene, and molybdenum disulfide (h-BN/G/MoS2) using ball milling and the sonication method and the investigation of their applicability for supercapacitor applications. The morphological investigation confirms the well-dispersed composite material production, and the ternary composite appears to be made of h-BN and MoS2 wrapping graphene. The electrochemical characterization of the prepared samples is evaluated by cyclic voltammetry and galvanostatic charge/discharge tests. With a high specific capacitance of 392 F g-1 at a current density of 1 A g-1 and an outstanding cycling stability with around 96.4% capacitance retention after 10,000 cycles, the ideal 5% BN_G@MoS2_90@10 composite demonstrates exceptional capabilities. Furthermore, a symmetric supercapacitor (5% BN_G@MoS2_90@10 composite) exhibits a 94.1% capacitance retention rate even after 10,000 cycles, an energy density of 16.4 W h kg-1, and a power density of 501 W kg-1. The findings show that the preparation procedure is safe for the environment, manageable, and suitable for mass production, which is crucial for advancing the electrode materials used in supercapacitors.

Detection of Acetaminophen in Groundwater by Laccase-Based Amperometric Biosensors Using MoS2 Modified Carbon Paper Electrodes

The use of enzyme-based biosensors for the detection and quantification of analytes of interest such as contaminants of emerging concern, including over-the-counter medication, provides an attractive alternative compared to more established techniques. However, their direct application to real environmental matrices is still under investigation due to the various drawbacks in their implementation. Here, we report the development of bioelectrodes using laccase enzymes immobilized onto carbon paper electrodes modified with nanostructured molybdenum disulfide (MoS2). The laccase enzymes were two isoforms (LacI and LacII) produced and purified from the fungus Pycnoporus sanguineus CS43 that is native to Mexico. A commercial purified enzyme from the fungus Trametes versicolor (TvL) was also evaluated to compare their performance. The developed bioelectrodes were used in the biosensing of acetaminophen, a drug widely used to relieve fever and pain, and of which there is recent concern about its effect on the environment after its final disposal. The use of MoS2 as a transducer modifier was evaluated, and it was found that the best detection was achieved using a concentration of 1 mg/mL. Moreover, it was found that the laccase with the best biosensing efficiency was LacII, which achieved an LOD of 0.2 µM and a sensitivity of 0.108 µA/µM cm2 in the buffer matrix. Moreover, the performance of the bioelectrodes in a composite groundwater sample from Northeast Mexico was analyzed, achieving an LOD of 0.5 µM and a sensitivity of 0.015 µA/µM cm2. The LOD values found are among the lowest reported for biosensors based on the use of oxidoreductase enzymes, while the sensitivity is the highest currently reported.

Interlayer-Expanded MoS2 Enabled by Sandwiched Monolayer Carbon for High Performance Potassium Storage

Potassium-ion batteries (PIBs) have aroused a large amount of interest recently due to the plentiful potassium resource, which may show cost benefits over lithium-ion batteries (LIBs). However, the huge volume expansion induced by the intercalation of large-sized potassium ions and the intrinsic sluggish kinetics of the anode hamper the application of PIBs. Herein, by rational design, nano-roses assembled from petals with a MoS2/monolayer carbon (C-MoS2) sandwiched structure were successfully synthesized. The interlayer distance of ultrathin C-MoS2 was expanded from original MoS2 of 6.2 to 9.6 Å due to the formation of the MoS2-carbon inter overlapped superstructure. This unique structure efficiently alleviates the mechanical strain, prevents the aggregation of MoS2, creates more active sites, facilitates electron transport, and enhances the specific capacity and K+ diffusion kinetics. As a result, the prepared C-MoS2-1 anode delivers a high reversible specific capacity (437 mAh g−1 at 0.1 A g−1) and satisfying rate performance (123 mAh g−1 at 6.4 A g−1). Therefore, this work provides new insights into the design of high-performance anode materials of PIBs.

Hydrothermally Grown MoS2 as an Efficient Electrode Material for the Fabrication of a Resorcinol Sensor

Recently, the active surface modification of glassy carbon electrodes (GCE) has received much attention for the development of electrochemical sensors. Nanomaterials are widely explored as surface-modifying materials. Herein, we have reported the hydrothermal synthesis of molybdenum disulfide (MoS₂) and its electro-catalytic properties for the fabrication of a resorcinol sensor. Structural properties such as surface morphology of the prepared MoS₂ was investigated by scanning electron microscopy and phase purity was examined by employing the powder X-ray diffraction technique. The presence of Mo and S elements in the obtained MoS₂ was confirmed by energy-dispersive X-ray spectroscopy. Finally, the active surface of the glassy carbon electrode was modified with MoS₂. This MoS₂-modified glassy carbon electrode (MGC) was explored as a potential candidate for the determination of resorcinol. The fabricated MGC showed a good sensitivity of 0.79 µA/µMcm² and a detection limit of 1.13 µM for the determination of resorcinol. This fabricated MGC also demonstrated good selectivity, and stability towards the detection of resorcinol.

Nitrogen-doped graphene-poly(hydroxymethylated-3,4-ethylenedioxythiophene) nanocomposite electrochemical sensor for ultrasensitive determination of luteolin

An ultrasensitive luteolin electrochemical sensor was constructed by co-electropolymerization of nitrogen-doped graphene (N-GR) and hydroxymethylated-3,4-ethylenedioxythiophene (EDOT-MeOH) using cyclic voltammetry (CV). Because of the synergistic effects of the large surface area, superior electrical conductivity, and large amount of chemically active sites of N-GR together with the satisfactory water solubility and high conductivity of poly(hydroxymethylated-3,4-ethylenedioxythiophene) (PEDOT-MeOH), the N-GR-PEDOT-MeOH nanocomposite sensor exhibited high electrochemical sensitivity towards luteolin with a wide linear range of 0.005-10.06 μM and low detection limit of 0.05 nM. Satisfactory reproducibility, selectivity, and stability were exhibited by this electrochemical sensor. Additionally, the proposed sensor was employed for trace-level analysis of luteolin in actual samples of herbal medicines (thyme (Thymus vulgaris L.), honeysuckle (Lonicera japonica Thunb.), and Tibetan Duyiwei (Lamiophlomis rotata (Benth.) Kudo)) with satisfactory results.

Coal-Derived Graphene/MoS2 Heterostructure Electrodes for Li-Ion Batteries: Experiment and Simulation Study

A novel coal-derived graphene-intercalated MoS₂ heterostructure was prepared with a facile in situ hydrothermal approach followed by high-temperature calcination. XRD, FE-SEM, HR-TEM, HR-Raman, and TOC analytical instruments, combined with first-principles simulations, were employed to explore the structural and electrochemical properties of this heterostructure for use as an electrode material. The XRD measurements and simulations confirmed the formation of the MoS₂/graphene (MoS₂-G) heterostructure. The microstructure analysis indicated that a well-defined 3D flower-like structure with tunable interlayer distances was created in the MoS₂ layer. The novel MoS₂-09% G anode exhibits a remarkable initial discharge capacity of ∼929 mAh/g due to its interlayer expansion from the intercalation of graphene between the MoS₂ layers. This anode maintains a capacity of ∼813 mAh/g with a Coulombic efficiency (CE) of ∼99% after 150 cycles at a constant current density of 100 mA/g. This anode also delivers a high-rate capability of ∼579 mAh/g at a current density of 2000 mA/g, significantly higher than that of other comparable structures. The unique flower-like arrangement, sufficient interlayer spacing for Li-ion diffusion, and the increased conductive matrix created using coal-derived graphene enhance the electrode kinetics during electrochemical reactions. Our first-principles calculations revealed that the diffusion barriers are significantly lower in heterostructures compared to that of bare MoS₂. This heterostructure design has significant potential as a new type of anode for Li-ion storage in next-generation batteries.

Insights and Perspectives Regarding Nanostructured Fluorescent Materials toward Tackling COVID-19 and Future Pandemics

The COVID-19 outbreak has exposed the world's preparation to fight against unknown/unexplored infectious and life-threatening pathogens. The unavailability of vaccines, slow or sometimes unreliable real-time virus/bacteria detection techniques, insufficient personal protective equipment (PPE), and a shortage of ventilators and many other transportation equipments have further raised serious concerns. Material research has been playing a pivotal role in developing antimicrobial agents for water treatment and photodynamic therapy, fast and ultrasensitive biosensors for virus/biomarkers detection, as well as for relevant biomedical and environmental applications. It has been noticed that these research efforts nowadays primarily focus on the nanomaterials-based platforms owing to their simplicity, reliability, and feasibility. In particular, nanostructured fluorescent materials have shown key potential due to their fascinating optical and unique properties at the nanoscale to combat against a COVID-19 kind of pandemic. Keeping these points in mind, this review attempts to give a perspective on the four key fluorescent materials of different families, including carbon dots, metal nanoclusters, aggregation-induced-emission luminogens, and MXenes, which possess great potential for the development of ultrasensitive biosensors and infective antimicrobial agents to fight against various infections/diseases. Particular emphasis has been given to the biomedical and environmental applications that are linked directly or indirectly to the efforts in combating COVID-19 pandemics. This review also aims to raise the awareness of researchers and scientists across the world to utilize such powerful materials in tackling similar pandemics in future.

Hierarchical structure of molybdenum disulfide-reduced graphene oxide nanocomposite for the development of a highly efficient serotonin biosensing platform

Molybdenum disulfide-reduced graphene oxide nanocomposite based immunosensor for the serotonin detection.

In situ growth of chrysanthemum-like NiCo2S4 on MXenes for high-performance supercapacitors and a non-enzymatic H2O2 sensor

In this work, we developed a novel strategy to couple chrysanthemum-like NiCo₂S₄in situ-grown MXene hybrids into a three-dimensional (3D) sandwich architecture hybrid as an electrode material for high-performance asymmetric supercapacitors and non-enzymatic H₂O₂ sensors. In the 3D sandwich architecture hybrid, the NiCo₂S₄ particles were encapsulated by MXene layers, which enhanced the interlayer space of MXene, significantly improving the electrochemical properties. In particular, the MXene/NiCo₂S₄ 1 : 2 electrode achieved a specific capacitance of 1266 F g^-1 at 0.5 A g^-1 and maintained 95.21% of its initial value after 10 000 cycles. Furthermore, an asymmetrical supercapacitor was also fabricated using MXene/NiCo₂S₄ 1 : 2 as the positive electrode and activated carbon (AC) as the negative electrode (MXene/NiCo₂S₄ 1 : 2//AC), which exhibited exceptional electrochemical performance. MXene/NiCo₂S₄ 1 : 2//AC exhibited a large specific capacitance of 621 F g^-1 at 0.5 A g^-1 and energy density of 72.82 W h kg^-1 at a power density of 0.635 kW kg^-1. In addition, MXene/NiCo₂S₄ 1 : 2 was employed as a non-enzymatic sensor for the electrochemical detection of H₂O₂, which exhibited a high sensitivity of 0.267 μA μM^-1 cm^-2 and noteworthy low detection limit of 0.193 μM based on 3 signal-noise ratios. This research provides a facile route for the in situ growth of bimetallic sulfides on MXenes as electrode materials for energy storage and electrochemical detection.

Differential pulse voltammetric determination of the carcinogenic diamine 4,4'-oxydianiline by electrochemical preconcentration on a MoS2 based sensor

An electrochemical sensor for the carcinogen 4,4'-oxydianiline (Oxy) is described. The method is based on the ability of MoS₂ nanosheets to preconcentrate Oxy. A glassy carbon electrode (GCE) was covered, by drop-casting, with MoS₂ nanosheets that were obtained by exfoliation. X-Ray photoemission spectroscopy indicates that Oxy accumulates on the MoS₂ nanosheets through an electropolymerization process similar to that reported for aniline. Both electrochemical impedance spectroscopy and atomic force microscopy were used to characterize the electrode surface at the different stages of device fabrication. Employing the current measured at +0.27 V vs. Ag/AgCl after Oxy adsorption, the modified GCE enables the voltammetric detection of Oxy at 80 nM levels with relative errors and relative standard deviations of <8.3 and <5.6%, respectively, at all the concentrations studied. The method was applied to the selective determination of Oxy in spiked river water samples. Very good selectivity and recoveries of around 95% in average are found. Graphical abstractSchematic representation of 4,4-oxydianiline electrochemical polymerization and preconcentration onto molybdenum disulfide nanosheets for the diamine determination in river waters.

Dy(III)-Based Metal-Organic Framework as a Fluorescent Probe for Highly Selective Detection of Picric Acid in Aqueous Medium

A dysprosium metal-organic framework, {[Dy(μ₂-FcDCA)_1.5(MeOH)(H₂O)]·0.5H₂O}_n (1), where FcDCA = 1,1'-ferrocene dicarboxylic acid, was prepared by slow-diffusion technique at room temperature. The crystal structure analysis of 1 by single-crystal X-ray diffraction reveals different binding modes of FcDCA linkers coordinated with Dy(III) metal ions, which forms continuous porous two-dimensional (2D) infinite framework. The resulting 2D layers are linked by π···π interactions to build three-dimensional (3D) supramolecular framework. Observably, this thermally stable 3D architecture was topologically simplified as a three-connected uninodal net with fes topology. Furthermore, the practical applicability of 1 was investigated as a fluorescence sensor for the sensitive detection of picric acid in aqueous medium with an impressive detection limit of 0.71 μM with quenching constant (K_SV) quantified to be 8.55 × 10⁴ M^-1. The distinguished selectivity in the presence of other nitroaromatics suggests the possible incorporation of 1 in real-world futuristic diagnostic kits. Additionally, the electrochemical behavior of 1 exhibits reversible in nature attributed to the ferrocene/ferrocenium cation.

Ultrafine Pt Nanoparticles Stabilized by MoS2/N-Doped Reduced Graphene Oxide as a Durable Electrocatalyst for Alcohol Oxidation and Oxygen Reduction Reactions

Direct alcohol fuel cells play a pivotal role in the synthesis of catalysts because of their low cost, high catalytic activity, and long durability in half-cell reactions, which include anode (alcohol oxidation) and cathode (oxygen reduction) reactions. However, platinum catalysts suffer from CO tolerance, which affects their stability. The present study focuses on ultrafine Pt nanoparticles stabilized by flowerlike MoS₂/N-doped reduced graphene oxide (Pt@MoS₂/NrGO) architecture, developed via a facile and cost-competitive approach that was performed through the hydrothermal method followed by the wet-reflux strategy. Fourier transform infrared spectra, X-ray diffraction patterns, Raman spectra, X-ray photoelectron spectra, field-emission scanning electron microscopy, and transmission electron microscopy verified the conversion to Pt@MoS₂/NrGO. Pt@MoS₂/NrGO was applied as a potential electrocatalyst toward the anode reaction (liquid fuel oxidation) and the cathode reaction (oxygen reduction). In the anode reaction, Pt@MoS₂/NrGO showed superior activity toward electro-oxidation of methanol, ethylene glycol, and glycerol with mass activities of 448.0, 158.0, and 147.0 mA/mg_Pt, respectively, approximately 4.14, 2.82, and 3.34 times that of a commercial Pt-C (20%) catalyst. The durability of the Pt@MoS₂/NrGO catalyst was tested via 500 potential cycles, demonstrating less than 20% of catalytic activity loss for alcohol fuels. In the cathode reaction, oxygen reduction reaction results showed excellent catalytic activity with higher half-wave potential at 0.895 V versus a reversible hydrogen electrode for Pt@MoS₂/NrGO. The durability of the Pt@MoS₂/NrGO catalyst was tested via 30 000 potential cycles and showed only 15 mV reduction in the half-wave potential, whereas the Pt@NrGO and Pt-C catalysts experienced a much greater shift (Pt@NrGO, ∼23 mV; Pt-C, ∼20 mV).

Detection of Triacetone Triperoxide (TATP) Precursors with an Array of Sensors Based on MoS₂/RGO Composites

Triacetone triperoxide (TATP) is a self-made explosive synthesized from the commonly used chemical acetone (C₃H₆O) and hydrogen peroxide (H₂O₂). As C₃H₆O and H₂O₂ are the precursors of TATP, their detection is very important due to the high risk of the presence of TATP. In order to detect the precursors of TATP effectively, hierarchical molybdenum disulfide/reduced graphene oxide (MoS₂/RGO) composites were synthesized by a hydrothermal method, using two-dimensional reduced graphene oxide (RGO) as template. The effects of the ratio of RGO to raw materials for the synthesis of MoS₂ on the morphology, structure, and gas sensing properties of the MoS₂/RGO composites were studied. It was found that after optimization, the response to 50 ppm of H₂O₂ vapor was increased from 29.0% to 373.1%, achieving an increase of about 12 times. Meanwhile, all three sensors based on MoS₂/RGO composites exhibited excellent anti-interference performance to ozone with strong oxidation. Furthermore, three sensors based on MoS₂/RGO composites were fabricated into a simple sensor array, realizing discriminative detection of three target analytes in 14.5 s at room temperature. This work shows that the synergistic effect between two-dimensional RGO and MoS₂ provides new possibilities for the development of high performance sensors.

Heterostructure of two different 2D materials based on MoS2 nanoflowers@rGO: an electrode material for sodium-ion capacitors

Sodium ion capacitors are under extensive investigation as companionable pre-existing lithium ion batteries and sodium ion batteries. Finding a suitable host for sodium ion storage is still a major challenge. In this context, here we report a MoS₂ nanoflowers@rGO composite produced via a hydrothermal method followed by an ultra sonication process as a sodium ion symmetric hybrid supercapacitor. The structural and electrochemical performances of the electrode material were investigated to establish its applicability in sodium ion capacitors. The electrochemical performance was evaluated using metallic sodium in a half cell configuration which delivered a maximum specific capacitance of 226 F g^-1 at 0.03 A g^-1. When examined as a symmetric hybrid electrode (full cell) it delivered a maximum capacitance of 55 F g^-1 at 0.03 A g^-1. This combination may be a new gateway for upcoming research work which deals with sodium ion storage applications. The results confirmed that the as-synthesized MoS₂ nanoflowers@rGO heterostructure electrode exhibited notable electrochemical behaviour.

Rosette-like MoS2 nanoflowers as highly active and stable electrodes for hydrogen evolution reactions and supercapacitors

MoS₂ is regarded as one of the cost-effective materials for many important applications. In this work, we report a simple one-step hydrothermal method for the directed synthesis of a rosette-like MoS₂ nanoflower modified electrode without using adhesion agents. Interestingly, owing to the hierarchical structures, the as-prepared MoS₂-based electrode exhibits significantly enhanced performance for both the hydrogen evolution reaction in acidic environments and supercapacitors. When used in the hydrogen evolution reaction, the electrode shows a low overpotential of ∼0.25 V at 10 mA cm⁻², a Tafel slope of ∼71.2 mV per decade, and long-term durability over 20 h of hydrogen evolution reaction operation at 10 mV cm⁻². In addition, as a supercapacitor electrode, it exhibits a good capacity of 137 mF cm⁻² at a current density of 10 mA cm⁻² and excellent stability in 1 M H₂SO₄ at a scan rate of 50 mV s⁻¹. The outstanding performances of the as-prepared materials may be ascribed to the unique 3D architectures of the rosette-like MoS₂ nanoflowers. This work could provide a strategy to explore low-cost and highly efficient electrocatalysts with desired nanostructures for the hydrogen evolution reaction and supercapacitors applications.

A simple strategy to synthesize interlayer spacing-enlarged rosette-like MoS₂ nanoflowers for both the hydrogen evolution reaction and supercapacitive energy storage.

Emerging Robust Heterostructure of MoS2-rGO for High-Performance Supercapacitors

The intermittent nature of renewable energy resources has led to a continuous mismatch between energy demand and supply. A possible solution to overcome this persistent problem is to design appropriate energy-storage materials. Supercapacitors based on different nanoelectrode materials have emerged as one of the promising storage devices. In this work, we investigate the supercapacitor properties of a molybdenum disulfide-reduced graphene oxide (rGO) heterostructure-based binder-free electrode, which delivered a high specific capacitance (387.6 F g^-1 at 1.2 A g^-1) and impressive cycling stability (virtually no loss up to 1000 cycles). In addition, the possible role of rGO in the composite toward synergistically enhanced supercapacitance has been highlighted. Moreover, an attempt has been made to correlate the electrochemical impedance spectroscopy studies with the voltammetric analyses. The performance exceeds that of the reported state-of-the-art structures.

Fluorographite to hydroxy graphene to graphene: a simple wet chemical approach for good quality graphene

Good quality graphene is prepared in a scalable manner from fluorographite by nucleophilic substitution of F with OH⁻ ions.

A highly selective and sensitive chemosensor forl-tryptophan by employing a Schiff based Cu(ii) complex

Construction of a new Cu(ii) complex (1) based modified glassy carbon electrode (1-GCE) for highly selective and sensitive detection ofl-tryptophan (l-Trp).